Fundamentals of Neurology: An Illustrated Guide

11. Diseases of the Cranial Nerves

Fundamentals

Disturbances of Smell (Olfactory Nerve)

Neurological Disturbances of Vision (Optic Nerve)

Disturbances of Ocular and Pupillary Motility

Lesions of the Trigeminal Nerve

Lesions of the Facial Nerve

Disturbances of Hearing and Balance; Vertigo

The Lower Cranial Nerves

Multiple Cranial Nerve Deficits

Image  Fundamentals

The cranial nerves can be affected by disease in isolation, or as a component of a wider disease process. Cranial nerve deficits are caused by lesions of their nuclei or tracts in the brainstem, or of the peripheral course of the nerves themselves and their branches.

The anatomical relationships of the cranial nerves to the base of the skull are shown in Fig. 3.3 (p. 17), while their anatomical course and distribution are summarized in Table 3.3 (p. 17). The causes and clinical manifestations of cranial nerve lesions are discussed in detail in this chapter.

Image  Disturbances of Smell (Olfactory Nerve)

Anatomy. The peripheral olfactory receptors can only be excited by substances dissolved in fluid. The receptors of the olfactory mucosa project their axons through the cribriform plate to the olfactory bulb(Fig. 3.3p. 17), which lies on the floor of the anterior cranial fossa, beneath the frontal lobe. After a synapse onto the second neuron of the pathway in the olfactory bulb, olfactory fibers travel onward through the lateral olfactory striae to the amygdalaand other areas of the temporal lobe. Olfactory fibers also travel by way of the medial olfactory striae to the subcallosal area and the limbic system.

Clinical manifestations. Techniques for examining the sense of smell are discussed on p. 16. Only the following types of olfactory disturbances are relevant to neurological diagnosis:

Anosmia. A more or less complete loss of the sense of smell is usually due to disorders of the nose, most commonly rhinitis sicca. The most common neurological cause of anosmia is traumatic brain injuryresulting in a brain contusion and/or traumatic avulsion of the olfactory fibers as they traverse the cribriform plate. The anosmia regresses in one-third of patients, but distortions of olfactory perception, so-called parosmias, often persist, sometimes in the form of unpleasant kakosmia (see below). Anosmia is the characteristic symptom of an olfactory groove meningioma and is often its initial manifestation. Rarer causes of hyposmia include Paget disease, Parkinson disease, prior laryngectomy, and diabetes mellitus. Medications often alter or impair the sense of smell. Anosmia always carries with it an impairment of the sense of taste (ageusia). The differential perception of gustatory stimuli requires not only an intact sense of taste, but also an intact sense of smell.

Olfactory hallucinations—usually in the form of spontaneous kakosmia—are produced by epileptic discharges from a focus in the anterior, medial portion of the temporal lobe. These hallucinations are sometimes called uncinate fits.

Image  Neurological Disturbances of Vision (Optic Nerve)

Visual disturbances can be caused by lesions of the retina or of its connections with the visual cortex. Depending on the etiology, the disturbance may consist of an impairment of visual acuity (ranging to total blindness) or a visual field defect, and these problems may appear either suddenly or gradually. In addition, the site of the lesion determines the type of visual field defect that will be present and whether it will affect only one eye or both. A simple clinical rule is that lesions of the retina and optic nerve impair visual acuity, while lesions of the optic chiasm and distal components of the visual pathway (from the optic tract to the visual-cortex) produce visual field defects, usually sparing visual acuity. Retrochiasmatic lesions impair visual acuity only when they are bilateral.

Visual Field Defects

A visual field defect is defined as the absence of some part of the normal visual field. The manual confrontation technique for examining the visual field is shown on p. 19 and the use of special instrumentation for this purpose is presented on p. 65.

The diagnostic assessment of a visual field defect involves, first, localization of the underlying lesion to a particular part of the visual pathway on the basis of the characteristics described above; and, second, determination of the etiology on the basis of the clinical history, other findings of the neurological examination, and the results of ancillary tests.

Types of visual field defect and their localization.

Visual field defects may be either monocular or binocular. Monocular visual field defects are caused by unilateral retinal lesions or by partial lesions of the optic n., while binocular ones are caused by unilateral lesions of the visual pathway from the optic chiasm onward (cf. Fig. 3.6p. 19).

The following types of visual field defect are characterized by their spatial configuration:

Image Hemianopsia: the defect occupies one half of the visual field (right or left).

Image Quadrantanopsia: the defect occupies one quarter of the visual field.

Image Scotoma: the defect occupies a small spot or patch within the visual field. So-called central scotoma is due to a lesion affecting the macula lutea or its efferent nerve fibers, resulting in an impairment of central vision and thus a reduction of visual acuity.

Image Temporal crescent: this is a preserved area of vision in the far lateral visual field on the side of a near-hemianopic visual field defect. The cause is a lesion of the contralateral occipital lobe sparing the rostral portion of the visual cortex on either side of the calcarine fissure.

Homonymous and heteronymous visual field defects. If a binocular visual field defect involves a corresponding area of the visual field in both eyes (e.g., the right half of the visual field in both eyes), it is called a homonymousvisual field defect. For example, a lesion of the right optic tract, lateral geniculate body, optic radiation, or visual cortex produces a left homonymous hemianopsia, while a lesion of any of these structures on the left produces a right homonymous hemianopsia (cf. Fig. 3.6p. 19). A lesion along the course of the optic radiation or in the visual cortex may affect only part of the radiating fibers or cortex, causing a homonymous defect that is less than a complete hemianopsia: thus, depending on the site and extent of the lesion, there may be a homonymous quadrantanopsia or homonymous scotoma.

In contrast, a lesion of the optic chiasm produces a heteronymous visual field defect: most such lesions affect the decussating fibers derived from the nasal half of each retina, thereby causing a bitemporal hemianop-sia or bitemporal quadrantanopsia. The visual field defect lies in the temporal half of each visual field, i. e., in the right half of the visual field of the right eye and the left half of the visual field of the left eye.

If a tumor, such as a pituitary adenoma, compresses the optic chiasm from below, there is initially an upper bitemporal quadrantanopsia, which is only later followed by bitemporal hemianopsia. If a tumor compresses the optic chiasm from above (e. g., a craniopharyngioma), there is initially a lower bitemporal quadrantanopsia, and later bitemporal hemianopsia.

If a tumor compresses the optic chiasm from one side, it will affect not only the decussating medial fibers, but also the uncrossed fibers from the retina on that side. The resulting visual field defect involves the entire visual field on the side of the lesion in addition to temporal hemianopsia on the opposite side.

Etiologic classification of visual field defects. A visual field defect that arises suddenly is generally due to either ischemia or trauma. The “gestalt” of the visual field defect, too, can provide a clue to its etiology: thus, a temporal crescent is highly characteristic of a vascular lesion. A slowly progressive visual field defect suggests the presence of a brain tumor. In such patients, the patient may fail to notice the visual field defect, particularly if the tumor lies in the right parietal lobe. There may be visual hemineglect accompanying, or instead of, a “true” visual field defect. The patient ignores visual stimuli in the affected hemifield, even though he or she may still be able to see them; and, if the patient truly cannot see stimuli in that hemifield, he or she is nonetheless unaware of the defect. Neuroimaging studies generally reveal the site and nature of the underlying lesion (Fig. 11.1).

Special types of visual field defect. In the Riddoch phenomenon, the patient cannot see stationary objects in the affected area of the visual field, though movement can be perceived. In palinopsia, the perception outlasts the stimulus: the patient continues to “see” the presented image long after it has been removed. This phenomenon is produced by right temporo-occipital lesions.

Image

Fig. 11.1 Infarct in the territory of the left posterior cerebral a. in a patient with right homonymous hemianopsia. MR image. a The axial T2-weighted image reveals abnormally bright signal in the cerebral cortex and in the underlying white matter, as well as a small hemorrhage within the infarct. b The diffusion-weighted MRI reveals diminished diffusion of protons and water molecules in the first few days after the event. Fresh infarcts are very well seen in this type of study. The hemorrhage, too, is visible in this case.

Impairment of Visual Acuity

Sudden unilateral loss of vision, as long as its cause does not lie in the eye itself, is usually due to a lesion of the optic nerve. The sudden onset of the defect implies that it has been caused by ischemia. A defect of this type may be permanent, e. g., in occlusion of the central retinal a. due to temporal arteritis or embolization from an atheromatous plaque in the carotid a., or it may be temporary, in which case it is called amaurosis fugax (transient monocular blindness). Rarely, transient visual loss can be produced by a disturbance of neural function, such as migraine (retinal migraine). Papilledema, too, can be accompanied by episodes of sudden visual loss (amblyopic attacks). Ocular causes should not be forgotten in the differential diagnosis, e. g., retinal detachment, preretinal hemorrhage, or central vein thrombosis. Correct diagnosis requires a precise clinical history and meticulous examination of the optic disc and fundus.

Sudden bilateral loss of vision may be due to bilateral retinal ischemia, e.g., on standing up in a patient with aortic arch syndrome. Certain types of intoxication can also rapidly produce bilateral optic nerve lesions, e. g., methanol poisoning, which causes blindness within hours. Yet, bilateral visual loss of more or less sudden onset is much more commonly due to simultaneous ischemia of both occipital lobes. Such events are often preceded by hemianopic episodes and loss of color vision as prodromal manifestations. The possible causes include embolization into the territory of the posterior cerebral aa. on both sides simultaneously and compressive occlusion of the posterior cerebral aa. by an intracranial mass. Patients often deny that they cannot see (anosognosia). Despite the severe visual loss, the pupillary light reflex is still present, because the pathway for visual impulses to the lateral geniculate body, where the fibers for the reflex branch off, remains intact. The visual evoked potentials (VEP, p. 56 and Fig. 4.19p. 59), however, are pathological.

Progressive impairment of visual acuity in one or both eyes. Unilateral impairment is due to a process causing more or less rapid, progressive damage to the optic nerve or chiasm. Retrobulbar neuritis(inflammation of the optic n. between the retina and the chiasm) and optic papillitis (inflammation of the optic n. at the level of the optic disc) cause unilateral visual loss within two days or a little longer. Progressive, unilateral visual loss should also always prompt suspicion of a mass: optic glioma, for example, is a primary tumor within the optic n. that is more common in children and an optic sheath meningioma can compress the nerve from outside. Retrobulbar neuritis rarely occurs bilaterally, sometimes in combination with myelitis. Further causes of bilateral loss of visual acuity are Leber hereditary optic atrophy and tobacco-alcohol amblyopia. In the latter condition, the most prominent initial finding is an inability to distinguish the colors red and green. Vitamin B12 deficiency can cause progressive optic atrophy in combination with polyneuropathy.

Pathological Findings of the Optic Disc

This is an area requiring close collaboration between the neurologist and the ophthalmologist.

Papilledema is usually a reflection of intracranial hypertension, but it can also be seen in infectious and inflammatory disorders, such as syphilis. The typical findings include a somewhat enlarged, hyperemic optic disc with blurred margins, enlarged veins, and usually hemorrhages (Fig. 11.2). Inexperienced clinicians often have difficulty distinguishing papilledema from other changes of the optic disc.

Optic nerve atrophy is a permanent residual finding after lesions of the optic n. The extent of visual loss, however, need not reflect the degree of visible atrophy. The optic disc is pale all the way to the disc margin, which remains sharp. These findings are typically seen after retrobulbar neuritis, for example (Fig. 3.4p. 18), but also after optic nerve compression (whether from outside, as by a meningioma, or from inside by an optic glioma). Further causes of optic nerve atrophy include chronic papilledema, syphilis, Leber hereditary optic nerve atrophy (LHON, a mitochondrial disease occurring in men), many types of spinocerebellar degeneration, ischemia, and exogenous intoxication.

Image

Fig. 11.2 Acute papilledema (left eye) in a patient with a brain tumor. The optic disc is swollen, with blurred margins and small, linear hemorrhages.

Image  Disturbances of Ocular and Pupillary Motility

Eye movements enable the fixation of gaze and the visual pursuit of objects that are in motion relative to the observer, whether the object itself of the observer is actually moving. The anatomical substrateof eye movements consists of the frontal and posterior eye fields, whose major projections descend to the paramedian pontine reticular formation (PPRF) on both sides of the pons. The PPRF, in turn, controls movements for horizontal gaze, as well as movements for vertical gaze through its interaction with the midbrain reticular formation. Vestibular afferent input and cerebellar connections also play important roles in the control of eye movements. Lesions of these supranuclear structures, whatever their etiology, cause horizontal or vertical gaze palsy or internuclear ophthalmoplegia. Clinically, it is important to distinguish nuclear from infranuclear disturbances of the oculomotor, trochlear, and abducens nerves, all of which can have a variety of causes. In addition, the motor functions of the brainstem, including eye movements, can also be disturbed in myasthenia gravis, muscle diseases, and orbital processes, any of which can cause diplopia. Pupillary motility can be altered by many different disease processes. Retinal and optic nerve lesions affect the afferent arm of the pupillary light reflex loop, while oculomotor nerve lesions affect its efferent arm. In the former case, the pupil constricts only upon illumination of the ipsilateral eye; in the latter case, the pupil is dilated and remains so regardless of which eye is illuminated. Loss of the sympathetic nerve supply to the eye causes Horner syndrome.

Fundamentals of Eye Movements

The anatomical substrate of eye movements consists of the following structures:

Image cortical areas in the frontal, occipital, and temporal lobes, in which the impulses for voluntary, conjugate eye movements and ocular pursuit movements are generated;

Image a number of important gaze centers in the brainstem (particularly the paramedian pontine reticular formation, PPRF, and midbrain nuclei) that relay the cortical impulses onward to the motor nuclei innervating the eye muscles in such a way that coordinated movements of the eyes can occur along the three major axes (horizontal, vertical, and rotatory movements). Special white matter tracts play an important role in this process, particularly the medial longitudinal fasciculus (MLF, Fig. 11.3);

Image finally, the motor nuclei and cranial nerves that innervate the eye muscles (cf. Fig. 3.8ap. 21);

Image the entire process is also affected by cerebellar impulses and by vestibular impulses that enter the central nervous system through the eighth cranial nerve.

Types of eye movement. Eye movements can be divided into the following types:

Image Saccades are rapid conjugate movements that are executed voluntarily or in reflex fashion in response to stimuli of various kinds. They serve to fix a new object in the center of vision. Small microsaccades have an angular velocity of 20°/s, larger ones up to 700°/s. Saccades are the elementary type of rapid eye movement.

Image Once the gaze has been fixated on a given object, slow pursuit movements serve to keep it in view if it is moving. The pursuit system is responsible for executing these conjugate eye movements: from the visual cortex in the occipital lobe, impulses travel to the eye fields of the temporal lobe (“medial superior temporal visual area,” MST) and the neighboring parietal cortex. These areas are interconnected with the paramedian pontine reticular formation (PPRF) and with the cerebellum. Impulses from the PPRF control the nuclei of the eye muscles either directly or by way of interneurons.

Image

Fig. 11.3 Anatomical substrate of conjugate eye movements. The diagram shows the anatomical pathways for a conjugate movement to the right: neural impulses flow from the cortical eye fields of the left hemisphere to the right PPRF and onward to the nucleus of the right abducens n. Impulses in the abducens n. induce contraction of the lateral rectus m. of the right eye. Meanwhile, cortical impulses also travel by way of the medial longitudinal fasciculus to the nucleus of the left oculomotor n., and impulses in this nerve induce contraction of the medial rectus m. of the left eye. Thus, lesions of the hemispheres or of the PPRF result in a palsy of conjugate horizontal gaze (hemispheric lesion: contralateral gaze palsy, PPRF lesion: ipsilateral gaze palsy). On the other hand, lesions of the medial longitudinal fasciculus cause an isolated loss of adduction of one eye during horizontal eye movement (internuclear ophthalmoplegia). Vertical eye movements are generated by the midbrain reticular formation (riMLF, p. 188), which receives input from both the cerebral cortex and the PPRF.

Image Disturbances of the pursuit system cause pursuit movements to break up into saccades. If the saccade system is also damaged, gaze palsy can result (see below).

Image Convergence movements serve to fix a nearby object in view and involve simultaneous adduction of both eyes.

Oculomotor Disturbances

Nystagmus

In purely descriptive terms, nystagmus is an involuntaryrepetitiverhythmic movement of the eyes. Nystagmus is often, but not always, pathological.

Image Nystagmus is sometimes physiological.

Examples of physiological nystagmus include optokinetic nystagmus (p. 186) and the type of vestibular nystagmus that is induced by rotation in a swivel chair. End-gaze nystagmus (p. 185) is also physiological, as long as it occurs symmetrically in both directions. Pathological nystagmus, on the other hand, indicates the presence of a lesion in the anatomical structures subserving eye movements. A large number of components in this system can be damaged and nystagmus has a correspondingly wide spectrum of possible causes (see below).

Phenomenological classification of nystagmus. As already discussed to some extent in Chapter 3, nystagmus can be characterized according to various criteria:

Image Jerk vs. pendular nystagmus: most types of nystagmus are either of the “jerking” type, i. e., with a fast and a slow phase, or pendular (back-and-forth).

Image Direction of beat in relation to the three major axes of eye movement: one speaks of horizontal, vertical, or rotatory nystagmus.

Image Direction of beat in relation to the midline of the eye: nystagmus may beat to the left, to the right, upward, downward, or diagonally.

Image In saltatory nystagmus, the direction of beat is defined, by convention, as that of the rapid phase, even though the slow phase is actually the pathological component and the rapid phase is a physiological correction for it, serving to return the eyes to their original position.

Image Nystagmus can be spontaneous (p. 185) or else present only in response to specific precipitating stimuli (e. g., position, change of position, a rotatory or thermal stimulus to the vestibular system, or a particular direction of gaze → gaze-evoked nystagmus, p. 185).

Image The examiner must also determine whether nystagmus is equally severe in both eyes, or whether it is weaker or perhaps nonexistent in one eye. Nystagmus that is unequal in the two eyes is also called dissociated nystagmus.

A mainly phenomenologically oriented listing and illustration of the most important types of nystagmus and their causes, is found in Table 11.1 and Fig. 11.4.

There are a few rarer types of nystagmus whose phenomenology is quite complex and not easily described by the criteria listed above. These types of nystagmus are summarized in Table 11.2.

Image

Topical classification of pathological nystagmus.

Often, the type of nystagmus that is present already provides a clue to the site of the lesion:

Image Gaze-paretic nystagmus. This type of nystagmus may be due to disease of the eye muscles themselves, or to a lesion of the cranial nerves innervating the eye muscles or of the corresponding brainstem nuclei. Gaze-paretic nystagmus is usually slow, coarse, and in the direction of the impairment of gaze.

Image Vestibular nystagmus is due to a lesion of the vestibular organ itself or of the vestibular n. or its nuclei in the brainstem. It typically appears as a spontaneous nystagmus beating away from the side of the lesion, regardless of the direction of gaze (nystagmus in a fixed direction, cf. Table 11.1). Vestibular nystagmus is typically inhibited by fixation; it is sometimes observable only if fixation is abolished by having the patient wear Frenzel goggles or shake the head rapidly.

Image Gaze-evoked nystagmus beats in the direction ofgaze and indicates a lesion in the brainstem or its afferent or efferent connections with the cerebellum. If caused by a unilateral cerebellar lesion, it can be highly asymmetrical or even beat only to the side of the lesion. In such patients, gaze-evoked nystagmus can be difficult to distinguish from vestibular nystagmus.

Image Nystagmus due to brainstem lesions. Vestibularspontaneous nystagmus, gaze-evoked nystagmus, upbeat or downbeat vertical nystagmus and positional and/or positioning nystagmus can all indicate the presence of a brainstem lesion. These types of nystagmus are often rotatory or dissociated (as in internuclear ophthalmoplegia).

Image

Fig. 11.4 The most important types of nystagmus. For each type of nystagmus, the figure shows the intensity and direction of beating, depending on the direction of gaze.

Image Positioning nystagmus is a predominantly rotatory nystagmus lasting several seconds after changes of position of a particular type; it is found in benign paroxysmal positioning vertigo, a disorder of the peripheral portion of the vestibular system (p. 202).

Image Congenital pendular nystagmus is characterized by conjugate, pendular eye movements that increase with attention or monocular fixation. It is normally well compensated. There is no underlying, pathological structural lesion.

Physiological nystagmus. The most important example is optokinetic nystagmus. This normal phenomenon serves to stabilize the visual image of a moving object on the retina and thus has the same purpose as the vestibulo-ocular reflex.

Optokinetic nystagmus consists of slow pursuit movements alternating with rapid return movements (saccades). The return movements occur whenever the moving object “threatens” to leave the visual field. If the object is moving very rapidly, optokinetic nystagmus can be voluntarily suppressed. Absent, asymmetrical, or dissociated optokinetic nystagmus is pathological.

Vestibulo-ocular reflex (VOR) is a function of the labyrinth that serves to stabilize gaze fixation on rapid movement of the head: it produces a compensatory eye movement in the direction opposite the head movement. Slower head movements do not need to be compensated for by the vestibular system, as the ocular pursuit system suffices to keep gaze fixated in this case (see above, p. 183). Vestibular nystagmus can be suppressed by fixation on an object moving in tandem with the head (nystagmus or VOR suppression test, see below). An inability to suppress the VOR by fixation is pathological.

Nystagmus suppression test (= VOR suppression test). In this test, the subject stretches both arms forward, holds his or her thumbs up, and fixates gaze on them. When the subject is then rapidly rotated around the long axis of the body, there is normally no nystagmus, because vestibular nystagmus can be suppressed by visual fixation (Fig. 11.5). If nystagmus does appear, this indicates a lesion in the cerebellum or its connections with the vestibular apparatus of the brainstem.

Image

Image

Fig. 11.5 Nystagmus suppression test. The patient extends the arms, fixates gaze on his or her own thumbs, and is then rapidly rotated “en bloc” by the examiner. In a normal individual, gaze fixation on the thumbs prevents the appearance of nystagmus. Failure to suppress nystagmus indicates a central lesion, usually in the cerebellum.

Supranuclear Oculomotor Disturbances

These disturbances are defined as those in which the voluntary movements and involuntary pursuit movements of both eyes are simultaneously impaired. The eyes generally remain parallel to each other, but they cannot be moved together in the horizontal or vertical plane. The lesion lies above the level of the cranial nerve nuclei and is thus “supranuclear.” In disorders of the brainstem, supranuclear lesions may coexist with nuclear lesions, so that a skew deviation can also be present.

Horizontal Gaze Palsy

A patient with horizontal gaze palsy cannot make a conjugate movement of the eyes to the right, to the left, or (rarely) in either direction. The causative lesion may be at any of several sites in the central nervous system:

Image cortical centers generating the impulses for horizontal gaze movements, particularly the frontal eye field of the frontal lobe;

Image the paramedian pontine reticular formation (PPRF), which receives the impulses from the higher cortical centers and relays them to the ipsilateral abducens n. nucleus (innervation of the lateral rectus m.) and simultaneously, by way of interneurons, to the contralateral oculomotor n. nucleus (innervation of the medial rectus m.). This projection lies within the medial longitudinal fasciculus (MLF, Fig. 11.3). The result is an ipsilateral, conjugate, horizontal gaze movement (i. e., to the left on activation of the left PPRF and to the right on activation of the right PPRF);

Image a lesion of the abducens n. nucleus has the same effect as a PPRF lesion, i. e., a conjugate horizontal gaze palsy to the side of the lesion (see above).

Lesions of the frontal eye field. This field occupies area eight in the middle frontal gyrus. The right eye field generates conjugate gaze movements to the left and the left eye field generates conjugate gaze movements to the right. When the frontal eye field is affected by an acute lesion, the influence of the contralateral field predominates for a few hours (or, rarely, days), so that the eyes (and the head) deviate to the side of the lesion: déviation conjuguée, the patient “looks at the lesion.” Déviation conjuguée is usually accompanied by contralateral hemiparesis.

Image

Fig. 11.6 Internuclear ophthalmoplegia (INO), left (diagram). When the patient looks straight ahead, the eyes are parallel. On attempted rightward gaze, the left medial rectus m. fails to contract (no adduction of the left eye) and there is nystagmus of the abducted right eye.

Active gaze movements toward the midline rapidly become possible again; so, later, do movements to the opposite side. As contralateral movements begin to re-emerge, they are accompanied by gaze-paretic nystagmus, whose rapid component beats away from the side of the lesion.

Lesions of the posterior hemispheric cortex. Horizontal gaze palsy due to an occipital lesion is often accompanied by hemianopsia. The gaze palsy is characterized by saccadization of ocular pursuit movements and optokinetic nystagmus (p. 185) is impaired.

Lesions of the paramedian pontine reticular formation (PPRF) affect the last supranuclear “relay station” for horizontal gaze movements. They usually cause long-lasting or permanent gaze palsy to the side of the lesion.

Lesion of the abducens n. nucleus affects not only the neurons whose axons constitute the sixth cranial nerve, but also interneurons that connect the nucleus by way of the adjacent medial longitudinal fasciculus (MLF) to the contralateral oculomotor n. nucleus, which innervates the contralateral medial rectus m. The clinical picture is initially very similar to that of a PPRF lesion. PPRF lesions, however, spare the vestibulo-ocular connections in the MLF and do not directly involve the cranial nerve nuclei subserving eye movement; thus, in PPRF lesions, the gaze palsy can be overcome by a vestibular stimulus. In contrast, gaze palsy due to a lesion of the abducens n. nucleus cannot be overcome either voluntarily or through any kind of reflex.

Vertical Gaze Palsy

Impairment of upward or downward conjugate gaze is always due to a midbrain lesion involving either the rostral interstitial nucleus of the medial longitudinal fasciculus (the Büttner–Ennever nucleus) or its efferent fibers (Fig. 11.3). In most patients, both upward and downward gaze are impaired, but pretectal lesions can cause isolated upward gaze palsy. Vertical gaze palsy is one of the clinical features of progressive supranuclear palsy (p. 130).

Internuclear Ophthalmoplegia

This condition is caused by a lesion of the medial longitudinal fasciculus (MLF). When the patient attempts to look away from the side of the lesion, the ipsilateral (adducting) eye cannot fully adduct, and the contralateral (abducting) eye exhibits end-gaze nystagmus. The inability of the ipsilateral eye to adduct is not due to a lesion of the oculomotor n. nucleus, as is demonstrated by a preserved ability to adduct (converge) in the near reflex. Internuclear ophthalmoplegia (INO) can also be bilateral if the MLF is damaged on both sides.

The diagram in Fig. 11.6 illustrates the clinical findings in internuclear ophthalmoplegia with total loss of adduction of the left eye. Fig. 11.7 shows a more common type of INO, in which the inward movement of the adducting eye is merely delayed and eventually takes place with slow, horizontal saccades. This type of INO is particularly common in multiple sclerosis.

One-and-a-Half Syndrome

This name is given to the combination of horizontal gaze paresis to one side (“one”) with internuclear ophthal-moplegia on attempted gaze to the other side (“half”). As one might expect, it is due to combined lesions of the PPRF or abducens n. nucleus on one side and of the ipsilateral MLF. The single horizontal eye movement that remains possible is abduction of the contralateral eye on attempted contralateral gaze.

Oculomotor Disturbances of Cerebellar Origin

These disturbances are listed in Table 11.3.

Other Supranuclear Disturbances of Eye Movement

Another disturbance worth mentioning here is oculomotor apraxia. In the congenital form (Cogan syndrome), the patient is unable, for example, to direct his or her gaze voluntarily to the beginning of a line of text while reading. Instead, the entire head must be moved into position so that the beginning of the line lands in the center of the visual field. Once this is done, the head can be moved back to its original position without loss of fixation on the text.

Lesions of the Nerves to the Eye Muscles and Their Brainstem Nuclei

Lesions of this type, like lesions of the eye muscles themselves, cause deviation of the axis of one eye, i. e., paralytic strabismus.

Oculomotor Nerve Palsy

An infranuclear lesion of the third cranial nerve causes paralysis of the medial, superior, and inferior rectus muscles, the inferior oblique mm., and the levator palpebrae m. (external ophthalmoplegia). In addition, the smooth muscle of the pupillary sphincter is paralyzed: the pupil is “fixed and dilated,” i. e., it is enlarged and responds neither to light, nor to convergence (internal ophthalmoplegia). The typical clinical aspect of oculomotor nerve palsy is thus immediately recognizable when the patient looks straight ahead (Fig. 11.8). The diagrams in Fig. 11.9 illustrate the typical findings in primary position and in the position of greatest deviation, as well as the positions of the two visual images depending on the patient's direction of gaze.

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Fig. 11.7 Right internuclear ophthalmoplegia in a patient with multiple sclerosis. In the initial phase of leftward gaze (upper photograph), only the left eye is abducted. The right eye follows, after a delay (lower photograph).

Table 11.3 Oculomotor disturbances due to cerebellar dysfunction

• saccadic pursuit

• diminished optokinetic nystagmus

• gaze-deviation nystagmus

• dysmetric saccades (under and overshoot)

• inability to suppress the oculovestibular reflex by fixation

• overshooting oculovestibular reflex

• special types of nystagmus, such as upbeat nystagmus, downbeat nystagmus, rebound nystagmus, periodically alternating nystagmus, acquired pendular nystagmus, central pos tional nystagmus, other types

• skew deviation

• unilateral cerebellar lesions produce nystagmus to the ipsilatral side (as in spontaneous vestibular nystagmus)

Image

Fig. 11.8 Complete left oculomotor palsy. a Severe ptosis of the left eye, which is also mildly abducted (predominant effect of lateral rectus m., innervated by the abducens n.). b The examiner lifts the ptotic eyelid to reveal the fixed (unreactive) pupil (paralysis of the parasympathetically innervated sphincter pupillae m.). (From: Mumenthaler, M.: Didaktischer Atlas der klinischen Neurologie. 2nd edn, Springer, Heidelberg 1986)

Image

Fig. 11.9 Right oculomotor nerve palsy. Note the position of the eyes and the position of the two visual images (diplopia) depending on the direction of gaze.

Table 11.4 Localization and etiology of oculomotor nerve palsy

Site of lesion

Clinical features

Etiology

 

Nuclear

oculomotor nerve palsy, bilateral vertical gaze palsy, bilateral ptosis

infarct, hemorrhage, trauma, tumor, multiple sclerosis, inflammation, congenital hypoplasia

Fascicular (nerve fibers within the brainstem)

oculomotor nerve palsy, contralateral hemi-paresis, ataxia or rubral tremor (differential diagnosis: transtentorial herniation)

infarct, hemorrhage, multiple sclerosis

Subarachnoid space

isolated oculomotor nerve palsy

aneurysm (internal carotid a., rarely other arteries such as the basilar a.), basilar meningitis, cranial polyradiculitis, intracranial hypertension, trauma, neurosurgical complication, tumor of the oculomotor n., transtentorial herniation

Cavernous sinus, superior orbital fissure, or orbit

oculomotor nerve palsy accompanied by dysfunction of CN IV, V/1, and VI in varying combinations

aneurysm (internal carotid a.), carotid-cavernous fistula, cavernous sinus thrombosis, parasellar tumor or pituitary tumor with para-sellar extension, sphenoid sinusitis, Tolosa-Hunt syndrome, herpes zoster

Orbital apex

oculomotor nerve palsy accompanied by dysfunction of CN II, IV, V/1, and VI in varying combinations

see lists of causes above and below (cavernous sinus, orbit)

Orbit

ptosis and superior rectus palsy (superior branch of CN III) or palsy of inferior and medial recti and inferior oblique mm. (inferior branch of CN III)

trauma, orbital tumor, orbital pseudotumor, infection, mucocele

No localizing significance

isolated external ophthalmoplegia (i. e., pupillary sparing)

diabetes, hypertension, arteritis, migraine

The third cranial nerve can be affected by a lesion at its nucleus in the brainstem (nuclear lesion), at various points along its course within the brainstem (fascicular lesion), or in the periphery (peripheral nerve lesion). There are many possible causes and the corresponding neurological deficits are correspondingly varied. Typical symptom constellations involving oculomotor nerve palsy and various other findings, depending on the location and etiology of the lesion, are presented in Table 11. 4. Lesions of the oculomotor n nucleus also cause bilateral ptosis and upward gaze paresis.

Trochlear Nerve Palsy

Lesions of the fourth cranial nerve cause paralysis of the superior oblique m. The patient can no longer depress the affected eye in adduction, or internally rotate it in abduction. The resulting diplopia arises when the patient looks down; the images are vertically displaced and slightly tilted. The typical clinical situation is shown schematically in Fig. 11.10. The two images can be brought together again by tilting the head to the normal side; the distance between the images increases if the head is tilted to the affected side (Bielschowsky phenomenon).

Image

Fig. 11.10 Right trochlear nerve palsy. Note the position of the eyes, the compensatory head tilt, and the position of the two visual images depending on the direction of gaze.

Image

Fig. 11.11 Right abducens nerve palsy. Note the position of the eyes, the compensatory rotation of the head, and the position of the two visual images depending on the direction of gaze.

Causes. The more common causes of trochlear nerve palsy are:

Image congenital aplasia,

Image trauma,

Image midbrain hemorrhage,

Image multiple sclerosis,

Image ischemic neuropathy of the nerve, e.g., in diabetes mellitus,

Image pathological processes in the cavernous sinus

Image or in the orbit.

Pathological processes affecting the superior oblique m. The tendon of the superior oblique m. changes direction in the trochlea, sliding within it in the manner of a pulley. The tendon can sometimes be caught in the ring of the trochlea, thus becoming “stuck” in the middle of a movement. This causes intermittent vertical diplopia, typically when the patient looks up just after looking down, and typically only lasting for a very short time (Brown syndrome). Myokymia of the superior oblique muscle may occur as a sequela of a trochlear nerve palsy, or independently. Its typical clinical sign is monocular, high-frequency nystagmus with oscillopsia and diplopia.

Abducens Nerve Palsy

Paralysis of the abducens m. caused by a lesion of the sixth cranial nerve causes inward strabismus of the affected eye. Horizontal diplopia is sometimes present even in the primary position of gaze and worsens as the patient looks toward the affected side. The findings are presented schematically in Fig. 11.11 and the more common causes are listed in Table 11.5.

Combined Lesions of Multiple Cranial Nerves Innervating the Muscles of Eye Movement, and Other Disorders in the Differential Diagnosis of Diplopia

If multiple cranial nerves innervating the muscles of eye movement on one side are affected, the lesion usually lies in the cavernous sinusat the orbital apexor in the orbit itself. Bilateral, multiple palsies of the muscles of eye movement are often due to brainstem processes; the differential diagnosis includes the entire spectrum of supranuclear oculomotor disturbances. In addition, disorders of neuromuscular transmission, such as myasthenia gravis (p. 275), and diseases of the eye muscles themselves must be considered, including myositis of the eye muscles (rare), mitochondrial myopathy (Kearns-Sayre syndrome), or endocrine ophthalmopathy in hyperthyroidism.

Table 11.5 Localization and etiology of abducens nerve palsy

Site of lesion

Clinical features

Etiology

 

Nuclear, pontine paramedian reticular formation

gaze palsy, often combined with peripheral or nuclear facial nerve palsy

infarct, hemorrhage, tumor, multiple sclerosis, inflammation, trauma, congenital aplasia

Fascicular

abducens palsy with contralateral hemiparesis, occasional also trigeminal deficit

infarct, hemorrhage, multiple sclerosis

Subarachnoid space

isolated abducens nerve palsy

intracranial hypertension, intracranial hypotension aneurysm (AICA, PICA, basilar a.), subarachnoid hemorrhage, basilar meningitis, cranial polyradicu tis, trauma, neurosurgical complication, tumor of the abducens n., clivus tumor

Petrous apex, petrous bone

deficits of CN V and VI, sometimes also VII and VIII

extradural infection in otitis media

Cavernous sinus, superior orbital fissure

abducens nerve palsy accompanied by dysfunction of CN III, IV, and V/1 in varying combinations

aneurysm (internal carotid a.), carotid-cavernous fistula, cavernous sinus thrombosis, parasellar tumor or pituitary tumor with parasellar extensio sphenoid sinusitis, Tolosa-Hunt syndrome, herpes zoster

Orbital apex

abducens palsy accompanied by dysfunction of CN III, IV, and V/1 in varying combinations

see lists of causes above and below (cavernous sinus, orbit)

Orbit

isolated lateral rectus palsy, or combined with other deficits

trauma, orbital tumor, orbital pseudotumor, endocrine ophthalmopathy, infection, mucocele

No localizing significance

isolated lateral rectus (abducens nerve) palsy

diabetes, hypertension, arteritis, migraine

Ptosis

Ptosis is present when the upper lid covers the upper border of the pupil. The cause of ptosis can be myogenicneurogenic, or mechanical (e.g., dehiscence of the levator aponeurosis).

The eyelid is actively elevated mainly by the action of the striated levator palpebrae m., which is innervated by the oculomotor n. Paralysis of this muscle causes ptosis that is most evident when the patient looks up. The eyelid is also held up, however, by the sympathetically innervated, smooth superior tarsal m. It follows that ptosis can be produced by lesions either of the oculomotor n. or of the sympathetic innervation of the eye. The causes of ptosis are listed in Table 11.6.

Horner syndrome is caused by loss of the sympathetic innervation of the eye and consists of:

Image ptosis (paralysis of the sympathetically innervated superior tarsal m.), most evident when the patient looks slightly downward;

Image miosis (paralysis of the sympathetically innervated dilator pupillae m.);

Table 11.6 Causes of ptosis

Pathogenesis

Causes (examples)

 

Mechanical factors

connective tissue defect (e. g., dehiscence of levator aponeurosis) local orbital change microphthalmia

Muscle disease

progressive external ophthalmoplegia Steinert myotonic dystrophy

Neuromuscular transmission disorder

myasthenia gravis botulism

Neurogenic: loss of innervation

oculomotor nerve lesion midbrain infarction cortical lesion sympathetic lesion (central or peripheral)

Neurogenic: excessively strong innervation

blepharospasm faulty regeneration after facial nerve palsy hemifacial spasm

Image mild enophthalmos (paralysis of Müller muscle, a smooth muscle in the orbit); and

Image conjunctival hyperemia (loss of the constrictive effect of the sympathetic nervous system on the conjunctival vessels).

When Horner syndrome is not accompanied by a loss of sweating in one-half of the face, the responsible lesion is located in the (ventral) roots of C8 through T2 proximal to their joining with the sympathetic chain. If it is accompanied by a loss of sweating in the face, neck, and arm on one side, then the lesion is at the stellate ganglion, or at a more cranial level of the sympathetic plexus in the neck. A lesion of the sympathetic chain immediately below the stellate ganglion impairs sweating in the ipsilateral upper quarter of the body without producing Horner syndrome. (It is worth noting that thoracic sympathectomy is sometimes performed at this site for the treatment of hyperhidrosis.)

Pupillary Disturbances

Pupillary motility is regulated by the parasympathetic portion of the oculomotor n. (sphincter pupillae m.) and by the sympathetic nervous system (ciliary m. = dilator pupillae m.). The constrictor and dilator muscles of the pupil are both smooth muscles; the parasympathetic nervous system constricts the pupil and the sympathetic nervous system dilates it. A lesion of the oculomotor n. thus produces a wide pupil, while a lesion of the sympathetic supply (e. g., in Horner syndrome) produces a narrow pupil.

Abnormalities of the Size and Shape of the Pupil

In pupillary ectopia, the pupil occupies an eccentric position in the iris. This may be due to a congenital malformation, an inflammatory disorder of the iris, or incomplete nerve regeneration after prior oculomotor nerve palsy. Abnormally shaped pupils are usually due to a congenital malformation. Mild inequality of pupillary size is a common, normal finding, but marked asymmetry is generally pathological. Inequality of the pupils is called anisocoria; its causes include Horner syndrome and Adie syndrome (see below) and others.

Abnormalities of the Pupillary Reflexes

Impairment of the direct and consensual pupillary light reflexes (p. 20) may be caused by any of the following:

Image Local affections of the eye, such as glaucoma or posterior synechiae.

Image The Marcus Gunn phenomenon is an impairment of the direct pupillary response to light on the side of a prior episode of retrobulbar neuritis.

Image Adie pupil (= pupillotonia) is usually unilateral, at least at first. The pupil is wider on the affected side and constricts very slowly in response to light, but promptly and completely on convergence. The subsequent widening of the pupil is slow (tonic). Women are more commonly affected than men; often, but not always, individual intrinsic muscle reflexes are absent. The pathogenesis of this condition is poorly understood. The underlying lesion is thought to lie either in the midbrain or in the ciliary ganglion.

Image Acute ciliary ganglionitis (after an infection or trauma) renders the pupil unresponsive to light or convergence.

Image Reflex pupillary rigidity (= Argyll Robertson pupil) is a typical finding in late neurosyphilis. The pupils are generally narrow, usually oblong, and unresponsive to light, but they constrict on convergence. It should be emphasized, however, that fixed and dilated pupils can also be seen in neurosyphilis.

Image The presence of a normal pupillary light reflex in a patient who is totally blind indicates bilateral damage to the visual pathway at some point between the lateral geniculate body and the visual cortex of the occipital lobe. The usual cause is bilateral infarction of the visual cortex. The light reflex is preserved because the nerve fibers subserving this reflex branch off the visual pathway proximal to the lateral geniculate body and travel to the pretectal area to innervate their target nuclei.

Image Hippus, a rhythmic fluctuation of pupillary width, is usually physiological.

The major abnormalities of pupillary size and responsiveness are summarized in Fig. 11.12.

Image

Fig. 11.12 Abnormalities of the pupillary reflexes (right side abnormal).

Image  Lesions of the Trigeminal Nerve

The trigeminal n. is responsible for the somatosensory innervation of the skin of the face and forehead and of many of the mucous membranes of the face and head. It also carries motor fibers innervating the muscles of mastication. Lesions of this nerve thus produce sensory deficits and paralysis of the muscles of mastication.

The anatomical course and distribution of the trigemi-nal n. are shown in Fig. 3.10p. 23 and the technique of clinical examination is presented on p. 22.

Clinical manifestations. Trigeminal lesions produce sensory deficits in the face and head. The somatosensory distribution of the three branches of the trigeminal n. are shown in Fig. 11.13. A lesion of the motor portion of the third branch causes paralysis of the muscles of mastication. The examiner can usually easily feel the diminished contraction of the masseter m. on one side. When the mouth is opened, the jaw deviates toward the paralyzed side because of weakness of the pterygoid mm. (Fig. 11.14).

Causes. Nuclear lesions of the trigeminal n. are located in the pons or medulla and are usually due to vascular processes, encephalitis, a focus of multiple sclerosis, or a space-occupying lesion (glioma, syringobulbia). The nerve can also be affected in its peripheral course by mass lesions, toxic influences, or mechanical (iatrogenic) factors. The trigeminal n. can also be affected as a component of cranial polyradiculitis. Occasionally, no clear cause can be found (idiopathic trigeminal neuropathy, which is usually unilateral). Trigeminal neuralgia is discussed below on p. 253.

Image

Fig. 11.13 Sensory innervation of the face and the mucous membranes of the head.

Image

Fig. 11.14 Lesion of the motor portion of the left trigeminal nerve. a Atrophy of the left temporalis and masseter muscles. b Deviation of the jaw to the left on opening.

Image  Lesions of the Facial Nerve

This mainly motor cranial nerve innervates the muscles of facial expression. It also provides taste to the anterior two-thirds of the tongue and innervates the lacrimal and salivatory glands. Lesions of the facial n. usually lie in the peripheral nerve trunk and are clinically evident mainly as facial palsy. Peripheral facial nerve palsy often arises without any apparent cause (i. e., it is often cryptogenic). It must always be carefully differentiated from symptomatic weakness of the facial musculature of central or peripheral origin.

The anatomical course of the seventh cranial nerve is depicted in Fig. 11.15.

Topical classification. The clinical picture of a (complete) facial nerve palsy depends on the site of the lesion:

Image Lesions distal to the sternomastoid foramen typically cause a purely motor paralysis of all of the muscles of facial expression on one half of the face. The eye cannot be closed (lagophthalmos) and the forehead cannot be wrinkled. No other deficit is present.

Image Lesions of the facial n. in the petrous portion of the temporal bone or in the facial (Fallopian) canal (the most common site) cause disturbances of lacrimation and salivation, impairment of taste, and/or hyperacusis in addition to the motor weakness of the face. All of these manifestations occur to varying extents depending on the precise location of the lesion.

Image

Fig. 11.15 Anatomy of the facial n. Note the bilateral central innervation of the cranial portion of the facial nerve nucleus. The caudal portion is only innervated by the contralateral hemisphere.

Image Lesions of the facial nerve nucleus or of its nerve fascicle within the brainstem are rarer and are mainly evident as a motor deficit including lagophthalmos and an inability to wrinkle the forehead. Lacrimation, salivation, and taste are normal, because the parasympathetic and gustatory fibers of the facial n. are derived from other cranial nerve nuclei in the brainstem.

Image Lesions above the facial nerve nucleus (= central facial palsy). The typical predominant finding in such cases is perioral weakness. The eye can still be closed on the affected side and the forehead can be symmetrically wrinkled.

Etiological classification. Cryptogenic facial palsy is the most common type and must be distinguished from other, symptomatic varieties. Its cause is unknown and is currently thought to be either a viral infection (e.g., by a herpesvirus) or a parainfectious process (see below). In symptomatic forms, a concrete cause for the facial palsy can be found: a basilar skull fracture, for example, can damage the facial n. Transverse fractures of the petrous bone cause immediate and often irreversible facial palsy. Longitudinal fractures frequently give rise to facial palsy only after a delay, usually because of a slowly expanding hematoma in the wall of the facial canal; the prognosis in such patients is better than in transverse fractures. Middle ear processes (cholesteatoma) can cause facial nerve palsy, as can skull base tumors and viral infections, particularly herpes zoster oticus. Borreliosis (Lyme disease) can affect the facial n. and produce a facial palsy. Bilateral facial palsy can be seen in (cranial) polyradiculitis. A nuclear facial nerve palsy results from infarction affecting the facial nerve nucleus in the pons, or from a brainstem glioma.

The most common type of peripheral facial palsy—the cryptogenic type—will now be described in detail.

Cryptogenic Peripheral Facial Nerve Palsy

Epidemiology. This condition (“Bell palsy”) accounts for three-quarters of all cases of facial palsy and has an annual incidence of ca. 25 per 100 000 individuals.

Etiology. The cause is unknown, but it is probably a viral infection. Swelling of the facial nerve trunk in the narrow confines of the facial canal leads to local com-pressive ischemia, which, in turn, leads to further swelling (a vicious circle). The result is a local interruption of the blood supply to the facial n. through the vasa nervorum and thus an extension of the ischemic injury, often leading to total axonotmesis.

Clinical manifestations. The most prominent finding is weakness of the muscles of facial expression, which can be of variable extent but is often complete, as depicted in Fig. 11.16. There is also an impairment of taste on the anterior two-thirds of the tongue on the affected side (for the technique of examination, cf. p. 22). “Bitter” tastes can usually still be perceived, because the receptors for this modality lie in the mucosa of the posterior third of the tongue, which is innervated by the glos-sopharyngeal n. Lacrimation and salivation are also ipsi-laterally impaired. Dysacusis or hyperacusis, due to denervation of the stapedius m., is hardly ever clinically evident.

Prognosis. The prognosis is generally favorable: in 80% of patients, the facial weakness resolves completely in four to six weeks. The remaining patients are those whose facial musculature has been completely denervated. For them, the recovery can take much longer (up to six months). Residual manifestations often include partial facial weakness or pathological accessory movements due to misdirection of regenerating axons. In cases of the latter type, active contraction of one part of the face is accompanied by simultaneous, involuntary contraction of another: thus, the patient's ipsilateral eye may close involuntarily when he or she whistles (synkinesia, Fig. 11.17).

Image

Fig. 11.16 Complete right peripheral facial nerve palsy (cryptogenic type). a At rest, the right corner of the mouth and the right cheek hang limply downward. b The patient cannot close the eye on the side of the weakness (right side). This is called lagophthalmos. The eye turns upward, and part of it remains visible (Bell phenomenon).

Image

Fig. 11.17 Mass innervation of the face after right peripheral facial nerve palsy. Because of faulty redirection of regenerating motor axons to their muscular targets, the active contraction of a muscle group in the face can be accompanied by involuntary contraction of other muscle groups. In the patient shown, whistling is accompanied by involuntary eye closure. (From: Mumenthaler, M.: Didaktischer Atlas der klinischen Neurologie. 2nd edn, Springer, Heidelberg 1986)

Differential diagnosis. Facial weakness of central origin must be distinguished from peripheral facial nerve palsy. In central weakness, the lesion lies above the level of the facial nerve nucleus, i. e., in the portion of the motor cortex subserving facial movements, or along the course of the corticobulbar efferent fibers. With meticulous clinical examination, one can always distinguish central from peripheral facial weakness; the criteria for making the distinction are summarized in Table 11.7. The most important one is the lesser involvement of the forehead and periocular musculature, compared with the remainder of the facial muscles, in central facial palsy.

The explanation is that the neurons in the superior portion of the facial nerve nucleus in the pons receive impulses from both cerebral hemispheres; therefore, a unilateral lesion of the motor cortex or corticobulbar tract can usually be compensated for by the corresponding, intact pathway on the opposite side (cf. Fig. 11.15). The caudal portion of the facial nerve nucleus, on the other hand, is “controlled” only by the contralateral hemisphere.

In addition, central facial palsy is often accompanied by weakness elsewhere in the body in areas not innervated by the facial n., e. g., in the tongue. If the tongue is weak on one side, it deviates, when protruded, to the side of the lesion (Fig. 11.18).

Image

Fig. 11.18 Left central facial palsy. a Impaired innervation of the lower portion of the face is evident when the patient tries to show his teeth. b As part of the central hemiparesis, the motor innervation of the left side of the tongue is also impaired, and the tongue therefore deviates to the left on protrusion.

Table 11.7 Differentiation of central and peripheral facial palsy

 

Central facial palsy

Peripheral facial palsy

 

History

Usually seen in elderly persons as a sudden, acute event; usually accompanied by hemiparesis mainly affecting the upper limb

May occur at any age; often accompanied by retroauricular pain; weakness develops over the course of one or two days, rather than suddenly

Facial appearance at rest

Usually normal

Often normal; blinking may be less frequent; the affected side of the face is flaccid in longstanding, complete peripheral facial palsy

Examination of facial musculature

The globe is always completely covered when the patient closes the eyes; the frontal branch is always much less affected

If the palsy is complete, the patient can never completely close the affected eye (though this is still possible in partial lesions of CN VII); the frontal branch is affected to the same extent as the rest of the nerve (Fig. 11.16)

Additional findings

There may be accompanying, ipsilateral weakness of the tongue, or central hemiparesis of the ipsilateral limbs

In the cryptogenic form, the sense of taste is lost on the ipsilateral side of the anterior two-thirds of the tongue; diminished lacrimation and salivation; electromyography reveals denervation

Hemifacial Spasm

This condition is characterized by synchronous, irregular, rapid, brief contractions of all of the muscles of facial expression supplied by the facial n. on one side of the face, particularly including the platysma. On close observation, hemifacial spasm is readily distinguishable from a facial tic (Fig. 11.19). It rarely arises in the aftermath of a peripheral facial nerve palsy. The usual cause is irritation of the facial nerve root by a looping blood vessel just distal to its point of exit from the pons; this explains why neurosurgical intervention (“microvascular decompression”) is usually successful. It is very rare for hemifacial spasm to be caused by a brainstem glioma. The condition can be treated symptomatically with an-ticonvulsants such as carbamazepine, or with injections of botulinus toxin.

Image

Fig. 11.19 Right hemifacial spasm in a 47-year-old patient. All of the muscles innervated by the facial nerve, including the platysma, contract repeatedly, synchronously, and involuntarily.

Image  Disturbances of Hearing and Balance; Vertigo

Lesions of the vestibulocochlear n. can impair hearing, balance, or both. A lesion of its cochlear portion produces sensorineural hearing loss (impairment of sound perception), which must always be differentiated from conductive hearing loss (impairment of sound conduction, usually due to blockage of the external auditory canal by cerumen, or to a disease process in the middle ear). A lesion of the vestibular portion causes disequilibriumand vertigo. Vestibular vertigo usually occurs in a particular direction and is accompanied by autonomic symptoms and nystagmus. Common vestibular disorders causing vertigo include vestibular neuritis and benign paroxysmal positioning vertigo. A vestibular lesion, however, is only one possible cause of vertigo; many other disorders must be included in the differential diagnosis.

The eighth cranial nerve (vestibulocochlear n.) conducts auditory and vestibular information to the central nervous system.

Image Auditory impulses arise in the organ of Corti in the cochlea and travel by way of the cochlear n. to the cochlear nuclei of the brainstem and then onward in the auditory pathway to the auditory cortex in the temporal lobe.

Image Vestibular impulses arise in the ampullae and in the macula statica of the saccule and utricle, the organ of equilibrium; they then travel by way of the vestibular n. to the vestibular nuclei, from which they are conducted to multiple areas of the brain, including the cerebellum.

These anatomical relations are depicted in Fig. 3.11 and discussed on p.24.

Neurological Disturbances of Hearing

The differentiation of sensorineural from conductive hearing loss helps determine whether the underlying cause is located in the middle ear or external auditory canal (more common sites, conductive hearing loss) or in the sensory cells of the inner ear or the neural apparatus of hearing (less common sites, sensorineural hearing loss). The method of examination and typical findings are summarized above on p. 22. The diagnosis and treatment of conductive hearing loss and of disorders of the cochlea are the responsibility of the otologist.

Neurological disturbances of hearing. Hearing loss due to a lesion of the inner ear or the vestibulocochlear n. may be unilateral or bilateral and its development may be more or less rapid:

Unilateral hearing loss, if acute, is usually due to an infectious process, e. g., mumps or other viral infection. If it is slowly progressive, the physician should suspect a mass lesion compressing the eighth cranial n., such as an acoustic neuroma or a meningioma in the cerebellopontine angle (Fig. 11.20). Larger masses in the cerebellopontine angle can affect not only the eighth cranial nerve, but also the facial and trigeminal nn.

Image

Fig. 11.20 Meningioma of the left cerebellopontine angle seen by MRI. The hazelnut-sized, spherical tumor is based on the pyramid of the petrous bone.

Bilateral hearing loss, if acute, is also most commonly due to a viral or other infection; bacterial meningitis is a rare cause. Progressive bilateral hearing loss, whether it is slow or rapid, should prompt suspicion of, e. g., chronic basilar meningitis (e. g., in tuberculosis), carcinomatous meningitis, an infectious disease (syphilis, toxoplasmosis), or an intoxication. Very slowly progressive, bilateral hearing loss may be due to a metabolic disorder, e.g., Refsum disease or one of the collagenoses.

A number of diseases that can produce hearing loss as their most prominent manifestation are listed in Table 11.8.

Tinnitus. Noises in one or both ears are a common complaint. They are usually subjective, i. e., audible only by the patient. They are termed objective when the examiner, too, can hear them with the stethoscope.

The most common variety of subjective tinnitus involves a noise heard continually in both ears. The patient usually finds it most disturbing in quiet surroundings, particularly in bed at night. The cause is unknown and the problem can resolve spontaneously. Various therapeutic measures have been proposed, including perfusion-enhancing medications and oxygen, but are of questionable benefit.

Table 11.8 Diseases causing prominent hearing loss

Category

Disease

Remarks

 

Hereditary congenital malformations of the inner ear

isolated hereditary deafness Mondini syndrome Alport syndrome Klein–Waardenburg syndrome Usher syndrome Laurence–Moon–Biedl syndrome mitochondrial encephalomyopathies

Most of these malformations are genetically transmitted in an autosomal recessive pattern, while a few are dominant or X-chromosomal. The inheritance pattern of mitochondrial encephalomy-opathies is nearly always strictly maternal, as these diseases are transmitted in mitochondrial DNA

Nonhereditary congenital malformations of the inner ear

thalidomide dysplasia measles embryopathy hyperbilirubinemia (kernicterus) perinatal asphyxia cretinism congenital syphilis toxoplasmosis

In thalidomide dysplasia and measles embryopathy, the ear anomalies are often accompanied by other anomalies elsewhere in the body. Kernicterus often causes athetosis; cretinism causes feeblemindedness

Infections

viral: herpes, mumps, measles, mononucleosis, HIV, and other neurotropic viruses bacterial meningitis otitis media and malignant otitis chronic otitis media, cholesteatoma syphilis, borreliosis

Hearing loss is a common late sequela of bacterial meningitis; otitis media causes conductive (not sensorineural) hearing loss; otoscopic examination is mandatory

Polyneuropathies combined with hearing loss

Refsum disease hereditary neuropathy (Charcot-Marie-Tooth)

Retinitis pigmentosa in Refsum disease

Tumors

acoustic neuroma glomus tympanicum tumor paraneoplastic

Acoustic neuroma occurs sporadically or as a component of neurofibromatosis, type I or II. The presenting symptom of a glomus tympanicum tumor is often pulsatile tinnitus

Cerebrovascular disorders

infarct in the territory of the labyrinthine a. migraine

 

Autoimmune disorders

collagen diseases Susac syndrome Cogan syndrome

Various types of autoantibody can be demonstrated in these conditions

Trauma

transverse fracture of petrous bone labyrinthine contusion acoustic trauma chronic exposure to noise barotrauma

The clinical history leads to the diagnosis

Toxic/iatrogenic

aminoglycosides, cytostatic agents

Usually bilateral, often with a bilateral vestibular deficit

Specific ear diseases

Ménière disease Lermoyez syndrome otosclerosis acute hearing loss perilymph fistula

In these conditions, vestibular symptoms are often present in combination (or in alternation) with hearing loss

Miscellaneous

superficial hemosiderosis of the CNS

Progressive hearing loss and ataxia

Pulsatile tinnitus is rare in comparison to continual tinnitus. It is caused by a pulsating blood vessel near the petrous bone and must be taken very seriously. The examiner, too, can often hear the pulse-synchronous bruit through a stethoscope (sometimes even without one). Some possible causes are listed in Table 11.9.

Disequilibrium and Vertigo

The vestibular organ (semicircular canals, saccule, and utricle) plays a central role in the regulation of balance. Disturbances of the vestibular apparatus (composed of the vestibular organ, the vestibulocochlear n., and the vestibular nuclei of the brainstem) cause dysequil-ibrium, the main symptom of which is vertigo. It must be emphasized, however, that vestibular disturbances are just one cause of vertigo (see below) and not even the most common one.

Regulation of equilibrium. Equilibrium (balance), i. e., the optimal static and dynamic mechanical stability of the human being in space, is maintained by the following neural processes:

Image impulses from the vestibular apparatus concerning the position, movement, and acceleration of the individual in space;

Image impulses from the visual system concerning the body's relation to visual space;

Image impulses from the exteroceptive pathways concerning the body's contact with underlying surfaces (floor, mattress, etc.);

Image impulses from the proprioceptive pathways concerning the positions of the joints and the spatial relations of the parts of the body to each other;

Image impulses concerning movements in the process of being executed, from the pyramidal, extrapyramidal, and cerebellar systems;

Image conscious (cognitive) and unconscious (emotional) influences;

Image finally, the integration of all of these signals in the brainstem.

The various components of the regulation of balance are depicted schematically in Fig. 11.21.

Table 11.9 Diseases that can present with pulsatile tinnitus

• Carotid dissection

• Fibromuscular dysplasia

• High-lying carotid stenosis due to atheromatous plaque

• Arteriovenous malformation

• Retromastoid dural fistula

• Carotid–cavernous fistula

• Glomus tumor (glomus jugulare or glomus tympanicum)

• Tumor in or near petrous bone

• Infection in or near petrous bone

• Intracranial hypertension

• Pseudotumor cerebri

Image

Fig. 11.21 The maintenance of balance by integration of information from multiple channels

Disturbances of the regulation of equilibrium. Vertigo arises if individual informational and/or control components of the regulatory system are lost (see below), if the information coming through different sensory channels seems to be incompatible (so-called multisensory mismatch, e. g., in seasickness), or the sensory input is highly unusual (e. g., uncommon visual input from a great height). So many different structures play a role in the maintenance of equilibrium and their interactions are so complex, that the causes of vertigo are, understandably, highly varied. Different types of vertigo result from lesions at different sites.

Types of vertigo. Directional vertigo (vestibular vertigo) is characteristic of lesions of the peripheral portion of the vestibular apparatus, i. e., the vestibular organ and/or the vestibulocochlear n. The patient perceives the environment as if it were in motion (= oscillopsia), e. g., rotating or heaving up and down like the deck of a boat. Vestibular vertigo is often accompanied by autonomic manifestations, such as nausea and vomiting, and by nystagmus. Central vestibular lesions (i. e., lesions of the vestibular nuclei in the brainstem) also cause directional vertigo, which is generally less intense than that due to peripheral lesions. The autonomic manifestations, too, tend to be milder or absent.

Image

Nonvestibular vertigo is nondirectional and often difficult for the patient to describe. The patient may report a woozy feeling, emptiness in the head, or darkness before the eyes. Oscillopsia is absent and there are usually no autonomic manifestations. Central nervous lesions can cause pathological nystagmus, as listed in Tables 11.1, 11.2. Nonvestibular vertigo is caused either by a lesion of the nonvestibular parts of the regulatory system for balance, or else by faulty information processing within the central nervous system (e. g., because of a cerebellar lesion). Pathological processes outside the central nervous system, such as orthostatic hypotension or aortic stenosis, can also cause nonvestibular vertigo.

The characteristic features of peripheral and central vestibular vertigo and of nonvestibular vertigo are summarized in Table 11.10.

Special aspects of history taking and diagnostic evaluation. The clinician should be able to tell whether the patient is suffering from vestibular or nonvestibular vertigo based on a meticulously elicited clinical history alone. It is also important to determine whether the vertigo is episodic or continuous and to ask about any precipitating factors (e. g., changes of position or particular situations that make the vertigo worse). If the vertigo worsens in the dark or when the patient's eyes are closed, the cause is likely to be a disturbance of proprio-ception (polyneuropathy, posterior column disease) or a bilateral vestibulopathy. The examiner should also always ask about accompanying symptoms (in particular, autonomic symptoms, tinnitus, hearing loss, and prior illnesses and infections). The history combined with the physical findings (nystagmus, results of balance tests, any other neurological abnormalities) usually allows localization of the functional disturbance. Further testing (e. g., caloric testing of the vestibular organ, ENT consultation, neuroimaging of the head) mainly serves to determine the etiology.

We will now describe the main neurological causes of vertigo, particularly vestibular disturbances, in greater detail.

Vestibular Vertigo

Acute loss of vestibular function is also called vestibular neuritis, acute vestibular neuropathy, or an acute vestibular crisis. It can be produced by a variety of pathogenetic mechanisms, the most common of which is a viral infection. The patient suddenly experiences acute rotatory vertigo with nauseavomiting, and falling to the side of the diseased vestibular organ. Every movement of the head makes the vertigo worse; therefore the patient, noting this, lies perfectly still. Examination reveals horizontally beatingspontaneous nystagmus in the direction opposite the side of the lesion, with a rotatory component. The nystagmus is more intense when the patient lies on the affected side; it can be diminished by visual fixation. The affected vestibular organ is less responsive than normal to caloric stimulation. Vertigo usually resolves fully within a few days, rarely within a few hours. Often a so-called “trigger labyrinth” remains as a residual phenomenon, i. e., vertigo on acceleration or rapid movements of the head. The condition may relapse.

Positional and positioning vertigo. These types of vertigo arise only with certain positions or positioning movements of the head and manifest themselves as brief attacks of vertigo that diminish in intensity if they are provoked in rapid succession. These conditions have a number of different causes.

Benign paroxysmal positioning vertigo is the most common type of positioning vertigo. It is provoked by changes in the position of the head, usually involving lying down rapidly, bending forward, turning in bed, or rapidly sitting up. It manifests itself as very brief (15–30 seconds) and very severe attacks of rotatory vertigo and nausea.

Image

Fig. 11.22 Hallpike positional testing for the demonstration of benign paroxysmal positioning vertigo. See text.

With respect to the pathogenesis of this condition, it is thought that small pieces of the otolith membranes of the saccule and utricle can break off and float freely in the endolymph—usually in the posterior semicircular canal, less commonly in the horizontal one. When the head is moved, these free particles move together with the endolymph and slide over the hair cells of the cupula, even after the movement is completed. The abnormally prolonged activation of the hair cells induces acute rotatory vertigo. The condition is also termed cupulolithiasis or canalolithiasis.

The Hallpike positioning maneuver can be used as a diagnostic test (Fig. 11.22). The patient is rapidly taken from an upright sitting position into the supine position with the head held down 30° below the level of the examining table and turned 60° to the right or left. Within a few seconds, the examiner should be able to observe rotatory nystagmus, which then disappears after 5–30 seconds. This is easiest to see if the patient is wearing Frenzel goggles. If the head is turned to the right, the nystagmus is counterclockwise; if to the left, clockwise.

Certain positioning maneuvers, e.g., those of Epley and Semont, have been shown to be useful as treatment for this condition. These maneuvers work by flushing the floating otoliths out of the affected semicircular canal.

Central positional vertigo is a rarer type of positionally dependent vertigo appearing with certain tilted positions of the head. The nystagmus usually beats to the uppermost ear and does not habituate on repeated provocation. The vertigo is generally not very severe.

Ménière disease is a common cause of acute vestibular vertigo. It is caused by endolymphatic hydrops and manifests itself clinically in episodes of acute rotatory vertigo, a tendencyto fall to the affected side, and horizontal, directional, spontaneous nystagmus, accompanied by nausea, vomiting, and tinnitus. Slowly progressive hearing loss is worse after each attack.

Bilateral vestibular deficits. While unilateral dysfunction of the vestibular apparatus can either recover or be compensated for by the intact opposite side within a matter of weeks, bilateral dysfunction deprives the regulatory system for balance of all incoming vestibular information. Consequently, the patient's gait becomes very unsteady in the dark (i. e., when visual input, too, is inoperative), or when the patient must walk on an uneven or soft surface (i.e., when the incoming proprioceptive information is difficult to interpret). Subjectively, the patient suffers from oscillopsia (apparent movement of the external world), particularly when walking, because the vestibulo-ocular reflex (p. 186) is inoperative and visual fixation is, therefore, unstable.

Nonvestibular Vertigo

Dysfunction of the nonvestibular components of the regulatory system for balance can also cause vertigo.

Image Visually induced vertigo occurs, e.g., when an individual looks down from a great height, or when the incoming proprioceptive information is inconsistent with the visual information (polysensory mismatch). The vertigo of seasickness is a type of visually induced vertigo.

Image Impaired proprioception, e.g., in polyneuropathy or posterior column disease, can also cause vertigo.

Image Cervical vertigo is thought to be due to faulty proprioceptive information arising in diseased cervical intervertebral joints or the adjacent soft tissues, which is then transmitted to the integrating apparatus for balance in the brainstem. This type of vertigo worsens in the dark. Its existence is debated.

Image Pathological processes affecting the central motor structures (e.g., paralysis, cerebellar or extrapyramidal disease, brainstem disorders) impair the patient's motor adaptation to changes in position, or cause oculomotor disturbances that can give rise to “dizziness.”

Image Partial impairment of consciousness, e. g., in presyn-cope or certain types of epilepsy (particularly temporal lobe epilepsy and absence seizures), is often experienced by the patient as “dizziness.”

Image Another frequent occurrence is psychogenic vertigo, particularly due to phobias, in the setting of depression, neurotic conflict situations, and panic attacks.

Image Finally, any general medical conditions that can temporarily diminish blood flow to the brain must be included in the differential diagnosis of “dizziness” andvertigo, e. g., arterial hypotension and heart disease.

Image  The Lower Cranial Nerves

Here we consider the clinical presentations of dysfunction of cranial nerves IX-XII. Lesions of the glossopharyngeal and vagus nn. produce dysphagiahoarseness, and dysphonia. Lesions of the accessory n., depending on their level, produce weakness of the sternocleidomastoid m. and trapezius m. Lesions of the hypoglossal n. produce ipsilateral weakness of the tongue.

Lesions of the Glossopharyngeal and Vagus Nerves

Anatomy. The anatomical course and distribution of these nerves is described above on p. 18.

Typical deficits. A unilateral lesion of the glos-sopharyngeal and vagus nn. causes ipsilateral weakness of the soft palate and posterior pharyngeal wall, which is evident as the curtain sign (Fig. 11.23, see also Fig. 3.13p. 26). The associated sensory deficit causes dysphagia and unilateral paralysis of the vocal cord causes hoarseness. The patient usually does not notice the loss of sensation in the external auditory canal or the loss of taste on the posterior third of the tongue.

Causes. Palsy affecting the ninth and tenth cranial nerves can be caused by infarction of the corresponding brainstem nuclei (e. g., in Wallenberg syndrome, p. Image). Lesions of the peripheral nerve trunks can be caused by a mass in the posterior fossa or by a bony fracture impinging on the nerves at their site of exit from the jugular foramen. In the latter case, the injury involves not only these nerves, but also the accessory n. (Siebenmann syndrome). Finally, isolated neuritis of these nerves can occur, e. g., in the setting of herpes zoster, or as a cryptogenic event.

Accessory Nerve Palsy

The anatomy and method of examination of the accessory n. are described above.

Typical deficits. A lesion of the purely motor main trunk of the accessory n. causes paralysis of the sternoclei-domastoid m. and of the upper portion of the trapezius m. (Fig. 11.24). Lesions of the accessory n. in the lateral triangle of the neck, however, are much more common. These spare the sternocleidomastoid m. and weaken only the upper portion of the trapezius m., causing a shoulder droop and an externally rotated position of the scapula (i. e., tilting of the caudal angle of the scapula toward the midline). This condition is depicted in Fig. 11.25.

Image

Fig. 11.23 Curtain sign revealing left-sided palatopharyngeal weakness in a 36-year-old patient with Wallenberg syndrome. a Normal appearance at rest. b Elicitation of the gag reflex is followed by pulling of the palate and posterior pharyngeal wall to the unaffected right side. (From: Mumenthaler M.: Didaktischer Atlas der klinischen Neurologie. 2nd edn, Springer, Heidelberg 1986.)

Causes. Dysfunction of the main trunk of the accessory n. is caused by mass lesions in the posterior fossa or at the base of the skull (Siebenmann syndrome, see above). Accessory nerve palsy due to interruption of the nerve in the lateral triangle of the neck is practically always iatrogenic, e. g., as a complication of lymph node biopsy at the posterior border of the sternocleidomastoid m.

Hypoglossal Nerve Palsy

The anatomy and technique of examination of the hypoglossal n. are described above on p. 27.

Typical deficits. The ipsilateral half of the tongue is paretic and, in the course of time, becomes atrophic. When the tongue is protruded, it deviates to the paretic side. This condition is illustrated in Fig. 3.16p. 27.

Causes. Unilateral hypoglossal nerve palsy is usually due to a bony fracture or a mass lesion—rarely, a congenital malformation—in the posterior cranial fossa. Carotid dissection is another possible cause. Rarely, isolated hypoglossal nerve palsy arises as a postinfectious or cryptogenic event.

Differential diagnosis. Unilateral tongue weakness can also be of central origin, i. e., due to a lesion of the corticobulbar pathway to the hypoglossal nerve nucleus (Fig. 11.18). Central weakness is unaccompanied by atrophy.

Bilateral tongue weakness and atrophy in the setting of true bulbar palsy (p. 80p. 155) is due to progressive loss of motor neurons in the nucleus of the hypoglossal nerve on both sides of the medulla. The observable abnormalities are slowly progressive and accompanied by fasciculations of the tongue.

Tongue weakness in pseudobulbar palsy (p. 80) is due to bilateral, usually ischemic damage of the central corticobulbar pathways. Because the lesion is central, no atrophy or fasciculations are seen. Examination reveals dysarthria, dysphagia, and abnormal prominence of the perioral reflexes.

Image

Fig. 11.24 Proximal left accessory nerve palsy with weakness of both the sternocleidomastoid m. and the trapezius m. a Even in the resting position, the upper edge of the trapezius m. is visibly thinner than on the right side, and the left sternocleidomastoid m. is barely discernible. b When the patient turns her head to the left, the intact right sternocleidomastoid m. is clearly seen. c When the head is turned to the right, there is only faint contraction of the left sternocleidomastoid m. (From: Mumenthaler M.: Didaktischer Atlas der klinischen Neurologie. 2nd edn, Springer, Heidelberg 1986.)

Image

Fig. 11.25 Lesion of the right accessory n. in the lateral triangle of the neck. a At rest, the right shoulder is somewhat lower, and the right scapula is somewhat farther from the midline. b When the arms are raised horizontally, the contour of the levator scapulae m. is easily seen below the atrophic edge of the trapezius m. c When the arms are raised vertically, the scapula tilts and the shoulder is low. d The atrophic upper edge of the trapezius m. is clearly seen in this frontal view. (From: Mumenthaler M.: Didaktischer Atlas der klinischen Neurologie. 2nd edn, Springer, Heidelberg 1986.)

Image  Multiple Cranial Nerve Deficits

Lesions affecting more than one cranial nerve at a time are seen in various typical combinations:

Image Progressive involvement of multiple lower cranial nerves (Garcin syndrome) is usually due to a tumor at the base of the skull. Chronic basilar meningitis, e. g., in tuberculosis, causes multiple cranial nerve palsies in varying combinations.

Image Cranial polyradiculitis affects the cranial nerves symmetrically; the most prominent manifestation is bilateral facial nerve palsy.

Image Further causes of multiple, and possibly recurrent, cranial nerve palsies include sarcoidosis, paraproteinemia, Wegener granulomatosis, malignant otitis, and others.