Atlas of Anatomy. Head and Neuroanatomy. Michael Schuenke

5. Topographical Anatomy

5.1 Face: Nerves and Vessels

This chapter describes the topographical anatomy of the anterior and lateral aspects of the head. It is assumed that the reader is already familiar with the skeletal, muscular, and neurovascular anatomy illustrated in previous chapters. The most clinically important regions around the eyes, nose, and ears are described in separate chapters. In this chapter the various regions of the face, head, and neck are displayed on the even- numbered pages (left-hand side), while the odd-numbered pages (right- hand side) provide information on functional groups of specific anatomical structures and their clinical importance.

A Superficial nerves and vessels of the anterior facial region

The skin and fatty tissue have been removed to demonstrate the superficial muscular layer, the muscles of facial expression. This layer has been partially removed on the left side of the face to display underlying portions of the muscles of mastication. The muscles of expression receive their motor innervation from the facial nerve, which emerges laterally from the parotid gland. The face receives its sensory innervation from the trigeminal nerve, whose three terminal branches are shown here (seeE). Branches from the third division of the trigeminal nerve additionally supply motor innervation to the muscles of mastication. The face receives most of its blood supply from the external carotid artery. Only small areas around the medial and lateral canthi of the eyes and in the forehead are supplied by the internal carotid artery (see B).

В Distribution of the external carotid artery (red) and internal carotid artery (brown) in the face

Hemodynamically significant anastomoses may develop between these two arterial territories. Even a marked reduction of flow in the internal carotid artery by atherosclerosis may not lead to cerebral ischemia, as long as there is adequate compensatory flow through the superficial temporal artery. If this is the case, then ligation of the superficial temporal artery is contraindicated (the artery might otherwise be ligated, for example, in a biopsy to confirm the diagnosis of temporal arteritis; see p. 59).

C Triangular danger zone in the face

This zone is marked by the presence of venous connections from the face to the dural venous sinuses. Because the veins in this region are valveless, there is a particularly high risk of bacterial dissemination into the cranial cavity (a boil may lead to meningitis—see p. 65).

D Clinically Important vascular relationships in the face

Note the connections between the exterior of the face and the dural sinuses.

If a purulent inflammation develops in the “danger zone” (see C), the angular vein can be

ligated at a standard site to prevent the transmission of infectious organisms to the cavernous sinus.

E Clinically important sites of emergence of the three trigeminal nerve branches

The trigeminal nerve (CNV) is the major somatic sensory nerve of the head. The diagram shows the sites of emergence of its three large sensory branches:

 branch of CN V^ supraorbital nerve (supraorbital foramen)

 branch of CN V2: infraorbital nerve (infraorbital foramen)

 branch of CN V3: mental nerve (mental foramen); see also p.77.

5.2 Head, Lateral View: Superficial Layer

A Superficial vessels and nerves of the head

Left lateral view. All the arteries visible in this diagram arise from the external carotid artery, which is too deep to be visible in this superficial dissection. The lateral head region is drained by the external jugular vein. The facial vein, however, drains into the deeper internal jugular vein (not shown here). The facial nerve has divided in the parotid gland to form the parotid plexus, whose branches leave the parotid gland at its anterior border and are distributed to the facial muscles (seeC). This lateral head region also receives sensory innervation from branches of the trigeminal nerve (see D), while the portion of the occiput visible in the drawing is supplied by the greater and lesser occipital nerves. Unlike the trigeminal nerve, the occipital nerves originate from the spinal nerves of the cervical plexus (see E). The secretory duct of the parotid gland (the parotid duct) is easy to identify at dissection. It passes forward on the masseter muscle, pierces the buccinator, and terminates in the oral vestibule opposite the second upper molar (not shown).

В Superficial branches of the external carotid artery

Left lateral view. This diagram shows the arteries in isolation to demonstrate their branches and their relationships to one another (compare with A; see p. 54 for details).

C Facial nerve (CN VII)

Left lateral view. The muscles of facial expression receive all of their motor innervation from the seventh cranial nerve (see p. 79).

D Trigeminal nerve (CN V)

Left lateral view. In the region shown here, the head derives its somatic sensory supply from three large branches of the trigeminal nerve (supraorbital nerve, infraorbital nerve, and mental nerve). The diagram illustrates their course in the skull and their sites of emergence in the anterior facial region (see the anterior view on p. 92). The trigeminal nerve is partly a mixed nerve because motor fibers travel with the mandibular nerve (= third division of the trigeminal nerve) to supply the muscles of mastication.

E Nerve territories of the lateral head and neck

Left lateral view.

Note: The lateral head and neck region receives its sensory supply from one cranial nerve (trigeminal nerve and its branches), and from the dorsal rami (greater occipital nerve) and ventral rami (lesser occipital nerve, great auricular nerve, transverse cervical nerve) of spinal nerves. The Cl spinal nerve has a ventral root, containing motor fibers, but no dorsal root; it therefore provides no sensory innervation to the skin (i.e., it has no dermatome).

5.3 Head, Lateral View: Middle and Deep Layers

A Vessels and nerves of the intermediale layer

Left lateral view. The parotid gland has been removed to demonstrate the structure of the intra parotid plexus of the facial nerve.

Note: certain nerves have been described in previous units.

The veins have been removed for clarity.

В Vessels and nerves of the deep layer

Left lateral view. The masseter muscle and zygomatic arch have been divided to gain access to the deep structures. Also, the ramus of the mandible has been opened to demonstrate the neurovascular structures that traverse it. The veins have been completely removed.

5.4 Infratemporal Fossa

A Left infratemporal fossa, superficial layer

Lateral view. A separate unit is devoted to the infratemporal fossa because of the many structures that it contains. The zygomatic arch and the anterior half of the mandibular ramus have been removed in this dissection to gain access to the infratemporal fossa. The mandibular canal has been opened, and the inferior alveolar artery and nerve can be seen entering the canal (the accompanying vein has been removed). The maxillary artery divides into its terminal branches deep within the infratemporal fossa (see B).

В Left infratemporal fossa, deep layer

Lateral view. This differs from the previous dissection in that both heads of the lateral pterygoid muscle have been partially removed, so that only their stumps are visible. The branches of the maxillary artery and mandibular division can be identified. By careful dissection, it is possible to define the site where the auriculotemporal nerve (branch of the mandibular division) splits around the middle meningeal artery before entering the middle cranial fossa through the foramen spinosum (seep. 59).

D Branches of the mandibular division in the infratemporal fossa

Left lateral view. The medial pterygoid muscle can be identified deep within the fossa. The third division of the trigeminal nerve passes through the foramen ovale from the middle cranial fossa to enter the infratemporal fossa. Traveling with it are motor fibers (motor root) that supply the muscles of mastication (only a few of the fibers are illustrated here).

E Variants of the left maxillary artery

Lateral view. The course of the maxillary artery is subject to considerable variation. The most common variants are listed below.

a Runs lateral to the lateral pterygoid muscle (common).

b Runs medial to the lateral pterygoid muscle.

c Runs medial to the buccal nerve but lateral to the lingual nerve and inferior alveolar nerve.

d Runs between the branches of the inferior alveolar nerve.

e Runs medial to the trunk of the inferior alveolar nerve.

5.5 Pterygopalatine Fossa

A Course of the arteries in the left pterygopalatine fossa

Lateral view. The infratemporal fossa (see previous unit, p. 98) is continuous with the pterygopalatine fossa shown here, with no clear line of demarcation between them. The anatomical boundaries of the pterygopalatine fossa are listed in B. The pterygopalatine fossa is a crossroad for neurovascular structures traveling between the middle cranial fossa, orbit, nasal cavity, and oral cavity (see the passageways in E). Because so many small arterial branches arise here, the arteries and veins have been shown separately for better clarity. The maxillary artery divides into its terminal branches in the pterygopalatine fossa (seep. 58). The maxillary artery can be ligated within the fossa for the control of severe nosebleed (epistaxis, see p. 119).

В Structures bordering the pterygopalatine fossa

Direction

Bordering structure

Anterior

Maxillary tuberosity

Posterior

Pterygoid process (lateral plate)

Medial

Perpendicular plate of the palatine bone

Lateral

Communicates with the infratemporal fossa via the pterygomaxillary fissure

Superior

Greater wing of the sphenoid bone, junction with the inferior orbital fissure

Inferior

Opens into the retropharyngeal space

C Larger branches of the maxillary artery

The maxillary artery consists of a mandibular part, pterygoid part, and pterygopalatine part. Because the vessels of the mandibular part lie outside the area of the dissection, they are not listed in the table below (see p. 58).

Branch

Distribution

 

Mandibular part see p. 58

   

Pterygoid part:

   

• Masseteric artery

• Masseter muscle

 

• Deep temporal arteries

• Temporalis muscle

 

• Pterygoid branches

• Pterygoid muscles

 

• Buccal artery

• Buccal mucosa

 

Pterygopalatine part:

 

• Posterior superior alveolar artery

• Maxillary molars, maxillary sinus, gingiva

 
 

• Infraorbital artery

• Maxillary alveolae

 

• Descending palatine artery

   

- Greater palatine artery

• Hard palate

 

- Lesser palatine artery

• Soft palate, palatine tonsil, pharyngeal wall

 
 

• Sphenopalatine artery

   

- Lateral posterior nasal arteries

• Lateral wall of nasal cavity, choanae

 
 

- Posterior septal branches

• Nasal septum

 

D Course of the nerves in the left pterygopalatine fossa

Lateral view. The maxillary division, the second division of CN V, passes from the middle cranial fossa through the foramen rotundum into the pterygopalatine fossa. Closely related to the maxillary nerve is the parasympathetic pterygopalatine ganglion, in which preganglionic fibers synapse with ganglion cells that, in turn, innervate the lacrimal glands and the small palatal and nasal glands. The pterygopalatine ganglion receives its presynaptic fibers from the greater petrosal nerve. This nerve is the parasympathetic root of the nervus intermedius branch of the facial nerve. The sympathetic fibers of the deep petrosal nerve (sympathetic root), like the sensory fibers of the maxillary nerve (sensory root), pass through the ganglion without synapsing.

E Passageways to the pterygopalatine fossa and transmitted neurovascular structures

Passageway

Comes from...

Transmitted structures

Foramen rotundum

Middle cranial fossa

• Maxillary nerve (CN V2)

Pterygoid canal

Base of the skull (inferior aspect)

• Nerve of pterygoid canal (greater and deep petrosal nerves)

• Artery of pterygoid canal with accompanying veins

Greater palatine canal

Palate

• Greater palatine nerve

• Descending palatine artery

• Greater palatine artery

Lesser palatine canals

Palate

• Lesser palatine nerves

• Lesser palatine arteries (terminal branches of descending palatine artery)

Sphenopalatine foramen

Nasal cavity

• Sphenopalatine artery (and accompanying veins)

• Medial and lateral superior and inferior posterior nasal branches (from nasopalatine nerve, CN V2)

Inferior orbital fissure

Orbit

• Infraorbital nerve

• Zygomatic nerve

• Orbital branches (from CN V2)

• Infraorbital artery (and accompanying veins)

• Inferior ophthalmic vein