Chapter 47: The scalp, auricle and face

Scalp

Layers.

The scalp (fig. 47-1) is comprised of five layers:

1. Skin, usually hairy.

2. Dense subcutaneous tissue containing vessels and nerves. The scalp gapes when cut, and the blood vessels are held open by the dense connective tissue, resulting in bleeding that should be arrested by pressure.

3. Aponeurosis and occipitofrontalis muscle. The galea aponeurotica (epicranial aponeurosis) is a fibrous helmet between the occipitalis and frontalis muscles and is anchored to the occipital bone. The occipitofrontalis muscle comprises two occipital bellies (attached to the occipital and temporal bones) and two frontal bellies (which end in the skin of the forehead), united by the galea and supplied by the facial nerve. The muscle moves the scalp and elevates the eyebrows.

4. Loose subaponeurotic tissue containing the emissary veins and allowing free movement of layers 1 to 3 as a unit. Layer 4 is a "dangerous area" because it allows spread of infection even, by way of the emissary veins, to intracranial structures.

5. Pericranium, the periosteum on the outside of the skull.

It should be noticed that the initial letters of the names of the layers form the word scalp.

Innervation and blood supply.

The nerves and vessels of the scalp (fig. 47-2) ascend in layer 2. Surgical flaps of the scalp are cut so as to remain attached inferiorly. The scalp is supplied successively by the branches of divisions 1 to 3 of the trigeminal nerve and by the cervical plexus and dorsal rami of the cervical nerves (see fig. 47-6). The trigeminal and cervical territories are commonly equal in area, but overlapping does occur. The arterial supply, although partly by the internal carotid artery, is mainly by branches of the external carotid artery. Anastomoses are abundant, so partially detached pieces of scalp may be replaced successfully. The superficial temporal artery, a terminal branch of the external carotid artery, arises in the parotid gland, crosses the zygomatic arch, and divides into frontal and parietal branches. The pulsations of the superficial temporal artery can be felt over the zygomatic arch. The posterior auricular and occipital arteries, also branches of the external carotid artery, run superiorward and posteriorward to the scalp.

Auricle

The auricle, a part of the external ear, consists of elastic cartilage covered by skin. The chief topographic features of the auricle are shown in figure 47-3. The lobule consists merely of fibrous tissue and fat. The auricle is connected with the fascia on the side of the skull by unimportant anterior, superior, and posterior auricular muscles, which are supplied by the facial nerve.

The auricle is supplied by both cranial (auriculotemporal nerve from cranial nerve V; probably also twigs from cranial nerves VII, IX, and X) and spinal (lesser occipital and great auricular) nerves (see fig. 47-6).

Face

The eyelids, nose, and lips are discussed elsewhere.

Muscles of facial expression (fig. 47-4).

The muscles of facial expression are very superficial (being attached to or influencing the skin) and are all supplied by the facial nerve. In addition to those of the scalp and auricle, already mentioned, muscles are arranged around the openings of the orbits, nose, and mouth.

The orbicularis oculi (fig. 47-4A), a sphincter around the rim of the orbit, comprises (1) an orbital part, attached mainly to the medial margin of the orbit; (2) a palpebral part, contained in the eyelids and anchored medially and laterally; and (3) a lacrimal part, posterior to the lacrimal sac. The orbicularis protects the eye and brings the eyelids together in blinking and sleep. Its antagonists are the levator palpebrae superioris and the frontalis muscles. Paralysis of the orbicularis causes drooping of the lower eyelid (ectropion) and spilling of tears (epiphora), as occurs in facial palsy.

The muscles around the nose and mouth are shown in figure 47-4B and C. The orbicularis oris is a complicated sphincter that closes the lips and can also protrude them. The buccinator arises from the maxilla and mandible and is inserted in a complicated manner into the orbicularis oris and lips. It is overlain by the buccal fat pad, and both are pierced by the parotid duct. The buccinator keeps the cheek taut, preventing injury from the teeth.

Facial nerve.

All the muscles of facial expression develop from pharyngeal arch 2 and hence are supplied by the facial nerve. The facial nerve traverses successively (1) the posterior cranial fossa, (2) the internal acoustic meatus, (3) the facial canal in the temporal bone, and (4) the parotid gland and face. After it gives off the posterior auricular nerve, the facial nerve divides within the parotid gland into its terminal branches, which form the parotid plexus. The branches emerge under cover of the parotid gland, radiate as they procede anteriorward in the face, communicate with the branches of the trigeminal nerve, and innervate the muscles of facial expression, including the platysma. The terminal branches are usually classified as temporal, zygomatic, buccal, marginal (along the mandible), and cervical (fig. 47-5A).

Facial artery.

The facial artery, a branch of the external carotid artery in the neck, winds around the inferior border of the mandible and proceeds superomedially on the face (fig. 47-5B). It is very tortuous and participates in many anastomoses. In the face, the facial artery supplies the lips (by inferior and superior labial arteries) and the anterior part of the nose and ends as the angular artery. This artery ends at the medial angle of the eye by anastomosing with branches of the ophthalmic artery, thereby establishing a communication between the external and internal carotid arteries. The labial arteries of the two sides anastomose across the median plane: hemorrhage from a cut lip is controlled by compressing both sides of the cut between the index fingers and thumbs.

Facial vein.

The facial vein (fig. 47-5B) is posterior to the artery, somewhat more superficial and is not as tortuous. Its origin, the angular vein, communicates with the cavernous sinus by way of the ophthalmic veins. In the cheek, the facial vein receives the deep facial vein from the pterygoid plexus, and it usually ends directly or indirectly in the internal jugular vein. Because of its connections with the cavernous sinus and the pterygoid plexus and the consequent possibility of spread of infection, the territory of the facial vein around the nose and upper lip has been termed the "danger area" of the face.

Cutaneous innervation of head and neck

The "vertex-ear-chin line" indicates the boundary between the cranial (trigeminal) and spinal innervations (fig. 47-6). The ophthalmic, maxillary, and mandibular branches of the trigeminal nerve separate before emerging from the base of the skull, and their cutaneous distributions must be tested separately; this is usually done over the forehead, the prominence of the cheek, and the chin.

The spinal innervation of the skin (see fig. 3-3) should be considered from the perspective of dermatomes and in terms of the supply by named peripheral nerves. Dermatomes may be considered as successive areas of distribution for each spinal nerve, both ventral and dorsal rami. Peripheral nerve distribution overlaps dermatomes because ventral rami combine to form plexi (e.g., the cervical plexus) in which the individual rami become regrouped to form named nerves (e.g., great auricular) (fig. 47-6).

Questions

47-1 List the layers of the scalp.

47-1 The layers of the scalp are as follows: skin, close subcutaneous tissue, aponeurosis (galea aponeurotica) and occipitofrontalis, loose subaponeurotic tissue, and pericranium. That the initial letters form the word scalp is an excellent mnemonic. Deep to the scalp are the skull, meninges and subarachnoid space, and cerebral cortex (see fig. 47-1).

47-2 What are the antagonists of the orbicularis oculi?

47-2 The antagonists of the orbicularis oculi are the levator palpebrae superioris and the frontalis.

47-3 Which is the main muscle of the cheek?

47-3 The buccinator is the main muscle of the cheek, which it keeps taut and free from the teeth. It is said to be concerned with whistling and blowing (L., buccinator, trumpeter). The buccinator and the more superficially placed masseter are overlain by the buccal fat pad, which contributes to the roundness of an infant's cheek and may aid in suckling. The pad and the buccinator are pierced by the parotid duct, which possesses a sphincter at that level (J. Bossy, L. Gaillard, and J.-P. Saby, J. Fr. Otorhinolaryngol., 14:71, 1965).

47-4 What is the orbicularis oris?

47-4 The orbicularis oris is a complicated sphincter that closes the lips and can also protrude them. It forms a ring (L., orbicularis, a small ring) around the mouth. Several sets of fibers are included: deeply, fibers from the buccinator; more superficially, fibers from the levator and depressor anguli oris and other small facial muscles; and fibers proper to the lips.

47-5 How do the facial muscles develop?

47-5 The facial muscles develop from pharyngeal arch 2 and hence are supplied by the facial nerve.

47-6 How is hemorrhage from a cut lip controlled?

47-6 Hemorrhage from a cut lip is controlled by compressing both parts between the index fingers and thumbs, because the labial arteries of the two sides anastomose across the median plane.

47-7 Why is the area around the nose and upper lip termed the "danger area" of the face?

47-7 The area around the nose and upper lip is termed the "danger area" of the face because it is drained by the facial vein, which is connected with the cavernous sinus. Thrombosis of the cavernous sinus is a dangerous condition.

47-8 What is the boundary line between the cranial and spinal areas of cutaneous innervation of the head and neck?

47-8 The "vertex-ear-chin line" is generally taken to indicate the boundary between the cranial (i.e., trigeminal) and spinal cutaneous territories of the head and neck (see fig. 47-6), but overlapping does occur.

47-9 What are the two main modes of spinal innervation of the skin?

47-9 The two main modes of spinal innervation of the skin are (1) by numbered nerves in dermatomes (e.g., C4) and (2) by named nerves (e.g., great auricular). Herpes zoster ("shingles") is believed to be a viral disease of dorsal root ganglia, resulting in a cutaneous eruption that corresponds to the distribution of the dorsal root fibers of the affected ganglion. The term herpes zoster in Greek means literally a creeping, girdle-shaped condition, and the word shingles comes from the Latin cingulum, a girdle. A very instructive series of photographs of successive dermatomes involved in herpes zoster can be found in K. Hansen and H. Schliack, Segmentale Innervation, Thieme, Stuttgart, 1962.

47-10 Where is the trigeminal ganglion and what is its significance?

47-10 The trigeminal ganglion (Gasser, eighteenth century) is situated in a dural recess, the cavum trigeminale (Meckel, 1748), on the petrous part of the temporal bone. It contains the cells of origin of most of the afferent fibers in the three divisions of cranial nerve V. Anyone of these divisions may be involved in herpes zoster. Specific, temporary pain in the trigeminal area (trigeminal neuralgia) may be paroxysmal in type (tic douloureux). These conditions are extremely complicated. (See, for example, R. Hassler and E. A. Walker, eds., Trigeminal Neuralgia, Thieme, Stuttgart, 1970.) The Latin word trigeminus ("triplets") was given to the nerve because of its three main divisions.

Figure legends

Figure 47-1 Section through the scalp, skull, and meninges

Figure 47-2 Innervation and blood supply of the scalp, superior aspect. In this instance the trigeminal territory extends posterior to the vertex of the head. The abundant arterial anastomoses are omitted. (After Grant.)

Figure 47-3 Right auricle, lateral aspect.

Figure 47-4 Muscles of facial expression. A, Anterior aspect, showing the muscles around the openings of the orbit and nose. B, Muscles of the mouth. The course of the fibers that constitute the orbicularis oris is shown schematically on the right half of the face. C, Lateral aspect, showing the muscles of the scalp and auricle. The orbicularis oculi and orbicularis oris are shown also. In A, B, and C the unbroken leaders indicate the bony attachments of the muscles. D, Left-sided facial paralysis caused by a lesion of the facial nerve at its exit from the skull. The patient has been asked to "shut the eyes" tightly and to open the mouth. Note the deviation of the lips, characteristic triangular shape of the mouth, and failure to close the affected eye. (From a photograph by Pitres and Testut.)

Figure 47-5 A, The facial nerve in the face. Variations are common, but two chief divisions (temporofacial and cervicofacial) are generally found. The intricacies of the parotid plexus have been omitted. B, The facial vessels in the face. The vein is posterior, more superficial, and less tortuous.

Figure 47-6 Cutaneous innervation of the head and neck. The vertex-ear-chin line separates the trigeminal territory from that of the cervical nerves. Although the central portion of the face is supplied by the trigeminal nerve only, it is believed that most of the skin of the face and neck "is supplied from a combination of trigeminal and upper cervical nerve roots" (L. Kruger and R. F. Young, in The Cranial Nerves, ed. by M. Samii and P. J. Jannetta, Springer, Berlin, 1981). A.-T., auriculotemporal n. (from the mandibular); GA, great auricular n. (C2, 3); asterisk, probably branches from cranial nerves and the vagus nerve; 1, 2, 3, ophthalmic, maxillary, and mandibular nn.; V-C, vertex-ear-chin line.

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