Atlas of Anatomy. Head and Neuroanatomy. Michael Schuenke

10. Sectional Anatomy of the Head

10.1 Coronal Sections, Anterior Orbital Margin and Retrobulbar Space

A Coronal section through the anterior orbital margin

Anterior view. This section of the skull can be roughly subdivided into four regions: the oral cavity, the nasal cavity and sinus, the orbit, and the anterior cranial fossa.

Inspecting the region in and around the oral cavity, we observe the muscles of the oral floor, the apex of the tongue, the neurovascular structures in the mandibular canal, and the first molar. The hard palate separates the oral cavity from the nasal cavity, which is divided into left and right halves by the nasal septum. The inferior and middle nasal conchae can be identified along with the laterally situated maxillary sinus. The structure bulging down into the roof of the sinus is the infraorbital canal, which transmits the infraorbital nerve (branch of the maxillary division of the trigeminal nerve, CN V2). The plane of section is so far anterior that it does not cut the lateral bony walls of the orbits because of the lateral curvature of the skull. The section passes through the transparent vitreous body, and three of the six extraocular muscles can be identified in the retro-orbital fat. Two additional muscles can be seen in the next deeper plane of section (B). The space between the two orbits is occupied by the ethmoid cells.

Note: The bony orbital plate is very thin (lamina papyracea) and may be penetrated by infection, trauma, and neoplasms.

In the anterior cranial fossa, the section passes through both frontal lobes of the brain in the most anterior portions of the cerebral gray matter. Very little white matter is visible at this level.

В Coronal section through the retrobulbar space

Anterior view. Here, the tongue is cut at a more posterior level than in A and therefore appears broader. In addition to the oral floor muscles, we see the muscles of mastication on the sides of the skull. In the orbital region we can identify the retrobulbar space with its fatty tissue, the extraocular muscles, and the optic nerve. The orbit communicates laterally with the іnfratemрога I fossa through the inferior orbital fissure. This section cuts through both olfactory bulbs in the anterior cranial fossa, and the superior sagittal sinus can be recognized in the midline.

10.2 Coronal Sections, Orbital Apex and Pituitary

A Coronal section through the orbital apex

Anterior view. The soft palate replaces the hard palate in this plane of section, and the nasal septum becomes osseous at this level. The buccal fat pad is also visible in this plane. Because the buccal pad is composed of fat, it is attenuated in wasting diseases; this is why the cheeks are sunken in patients with end-stage cancer. This coronal section is slightly angled, producing an apparent discontinuity in the mandibular ramus on the leftside of the figure (compare with the continuous ramus on the right side).

В Coronal section through the pituitary

Anterior view. The nasopharynx, oropharynx, and laryngopharynx can now be identified. This section cuts the epiglottis, below which is the su- praglottic space. The plane cuts the mandibular ramus on both sides, and a relatively long segment of the mandibular division (CN V3) can be identified on the left side. The paired sphenoid sinuses are visible, separated by a median septum. Above the roof of the sphenoid sinuses is the pituitary (hypophysis), which lies in the hypophyseal fossa. In the cranial cavity, the plane of section passes through the middle cranial fossa. Due to the presence of the carotid siphon (a 180° bend in the cavernous part of the internal carotid artery), the section cuts the internal carotid artery twice on each side. Cranial nerves can be seen passing through the cavernous sinus on their way from the middle cranial fossa to the orbit. The superior sagittal sinus appears in cross-section at the attachment of the falx cerebri. At the level of the cerebrum, the plane of section passes through the parietal and temporal lobes. Intracerebral structures appearing in this section include the caudate nucleus, the putamen, the internal capsule, and the anterior horn of each lateral ventricle.

10.3 Transverse Sections, Orbits and Optic Nerve

A Transverse section through the upper level of the orbits

Superior view. The highest section in this series displays the muscles in the upper level of the orbit (the orbital levels are described on p. 136 ff). The section cuts the bony crista galli in the anterior cranial fossa, flanked on each side by cells of the ethmoid sinus. The sections of the optic chiasm and adjacent optic tract are parts of the diencephalon, which surrounds the third ventricle at the center of the section. The red nucleus and substantia nigra are visible in the mesencephalon. The pyramidal tract descends in the cerebral peduncles. The section passes through the posterior (occipital) horns of the lateral ventricles and barely cuts the vermis of the cerebellum in the midline.

В Transverse section through the optic nerve and pituitary

Superior view. The optic nerve is seen just before its entry into the optic canal, indicating that the plane of section passes through the middle level of the orbit. Because the nerve completely fills the canal, growth disturbances of the bone at this level may cause pressure injury to the nerve. This plane cuts the ocular lenses and the cells of the ethmoid labyrinth. The internal carotid artery can be identified in the middle cranial fossa, embedded in the cavernous sinus. The section cuts the oculomotor nerve on either side, which courses in the lateral wall of the cavernous sinus. The pons and cerebellar vermis are also seen. The falx cerebri and tentorium cerebelli appear as thin lines that come together at the straight sinus.

10.4 Transverse Sections, Sphenoid Sinus and Middle Nasal Concha

A Transverse section through the sphenoid sinus

Superior view. This section cuts the infratemporal fossa on the lateral aspect of the skull and the temporalis muscle that lies within it. The plane passes through the lower level of the orbit, and a small portion of the eyeball is visible on the left side. The orbit is continuous posteriorly with the inferior orbital fissure. This section displays the anterior extension of the two greater wings of the sphenoid bone and the posterior extension of the two “petrous bones" (petrous parts of the temporal bones), which mark the boundary between the middle and posterior cranial fossae (see p. 12 f). The clivus is part of the posterior cranial fossa and lies in contact with the basilar artery. The pontine origin of the trigeminal nerve and its intracranial course are clearly demonstrated.

В Transverse section through the middle nasal concha

Superior view. This section below the orbit passes through the infraorbital nerve in the accordingly named canal. Medial to the infraorbital nerve is the roof of the maxillary sinus. The zygomatic arch is visible in its entirety, and portions of the muscles of mastication medial to the zygomatic arch (masseter, temporalis, and lateral pterygoid) can be seen. The plane of section passes through the upper part of the head of the mandible. The mandibular division (CN V3) appears in cross-section in its bony canal, the foramen ovale. It is evident that the body of the sphenoid bone forms the bony center of the base of the skull. The facial nerve and vestibulocochlear nerve emerge from the brainstem. The dentate nucleus lies within the white matter of the cerebellum. The space around the anterior part of the cerebellum, the pontocerebellar cistern, is filled with cerebrospinal fluid in the living individual. The transverse sinus is prominent among the dural sinuses of the brain.

10.5 Transverse Sections, Nasopharynx and Median Atlantoaxial Joint

A Transverse section through the nasopharynx

Superior view. This section passes through the external nose and portions of the cartilaginous nasal skeleton. The nasal cavities communicate with the nasopharynx through the choanae. Cartilaginous portions of the pharyngotympanic tube project into the nasopharynx. The arterial blood vessels that supply the brain can also be seen: the internal carotid artery and vertebral artery.

Note the internal jugular vein and vagus nerve, which pass through the carotid sheath in company with the internal carotid artery.

A number of cranial nerves that emerge from the skull base are displayed in cross-section, such as the facial nerve coursing in the facial canal. This section also cuts the auricle and portions of the external auditory canal.

В Transverse section through the median atlantoaxial joint

Superior view. The section at this level passes through the connective- tissue sheet that stretches over the bone of the hard palate. Portions of the upper pharyngeal muscles are sectioned close to their origin. The neurovascular structures in the carotid sheath are also well displayed. The dens of the axis articulates in the median atlantoaxial joint with the facet for the dens on the posterior surface of the anterior arch of the atlas. The transverse ligament of the atlas that helps to stabilize this joint can also be identified. The vertebral artery and its accompanying veins are displayed in cross-section, as is the spinal cord. In the occipital region, the section passes through the upper portion of the posterior neck muscles.

10.6 Midsagittal Section, Nasal Septum and Medial Orbital Wall

A Midsagittal section through the nasal septum

Left lateral view. The midline structures are particularly well displayed in this plane of section, and the anatomical structures at this level can be roughly assigned to the facial skeleton or neurocranium (cranial vault). The lowest level of the facial skeleton is formed by the oral floor muscles between the hyoid bone and mandible and the overlying skin. This section also passes through the epiglottis and the larynx below it, which are considered part of the cervical viscera. The hard and soft palate with the uvula define the boundary between the oral and nasal cavities. Posterior to the uvula is the oropharynx. The section includes the nasal septum, which divides the nasal cavity into two cavities (sectioned above and in front of the septum) that communicate with the nasopharynx through the choanae. Posterior to the frontal sinus is the anterior cranial fossa, which is part of the neurocranium. This section passes through the medial surface of the brain (the falx cerebri has been removed). The cut edge of the corpus callosum, the olfactory bulb, and the pituitary are also shown.

Note the median atlantoaxial joint (whose stability must be evaluated after trauma to the cervical spine).

В Sagittal section through the medial orbital wall

Left lateral view. This section passes through the inferior and middle nasal conchae within the nasal cavity. Above the middle nasal concha are the ethmoid cells. The only parts of the nasopharynx visible in this section are a small luminal area and the lateral wall, which bears a section of the cartilaginous portion of the pharyngothympanic tube. The sphenoid sinus is also displayed. In the region of the cervical spine, the section cuts the vertebral artery at multiple levels. The lateral sites where the spinal nerves emerge from the intervertebral foramina are clearly displayed.

10.7 Sagittal Sections, Inner Third and Center of the Orbit

A Sagittal section through the inner third of the orbit

Left lateral view. This section passes through the maxillary and frontal sinuses while displaying one ethmoid cell and the peripheral part of the sphenoid sinus. It passes through the medial portion of the internal carotid artery and submandibular gland. The pharyngeal and masticatory muscles are grouped about the cartilaginous part of the pharyngotym panic tube. The eyeball and optic nerve are cut peripherally by the section, which displays relatively long segments of the superior and inferior rectus muscles. Sectioned brain structures include the external and internal capsules and the intervening putamen. The amygdala and hippocampus can be identified near the base of the brain. A section of the trigeminal ganglion appears below the cerebrum.

В Sagittal section through the approximate center of the orbit

Left lateral view. Due to the obliquity of this section, the dominant structure in the oral floor region is the mandible while the oral vestibule appears as a narrow slit. The buccal and masticatory muscles are prominently displayed in this plane. Much of the orbit is occupied by the eyeball, which appears in longitudinal section. Aside from a few sections of the extraocular muscles, the orbit in this plane is filled with fatty tissue. Both the internal carotid artery and the internal jugular vein are demonstrated. Except for the foot of the hippocampus, the only visible cerebral structures are the white matter and cortex. The facial nerve and vestibulocochlear nerve can be identified in the internal auditory canal.