Chapter 48: The parotid, temporal and infratemporal regions
The parotid region (see fig. 50-2C) comprises the parotid gland and its bed, which includes muscles and part of the skull. The temporal region is on the side of the head (temple). The infratemporal region is medial to the ramus of the mandible.
The parotid gland is the largest of the salivary glands, which include the also-paired submandibular and sublingual glands and numerous small glands in the tongue, lips, cheeks, and palate (fig. 48-1). Their combined secretion is termed saliva. The parotid, a serous compound tubulo-alveolar gland, is yellowish, lobulated, and irregular in shape. It occupies the interval between the sternomastoid muscle and the mandible.
The parotid gland lies inferior to the zygomatic arch, anteroinferior to the external acoustic meatus, anterior to the mastoid process, and posterior to the ramus of the mandible.
The parotid gland is enclosed in a sheath (parotid fascia) and is shaped roughly like an inverted pyramid, with three (or four) sides (fig. 48-2A). It has a base (from which the superficial temporal vessels and auriculotemporal nerve emerge), apex (which descends inferior and posterior to the angle of the mandible), and lateral, anterior, and posterior (or posterior and medial) surfaces. The lateral surface is superficial and contains lymph nodes. The anterior surface is grooved by the ramus of the mandible and masseter (fig. 48-2B), producing a medial lip (from which the maxillary artery emerges) and a lateral lip, under cover of which the parotid duct, branches of the facial nerve, and the transverse facial artery emerge (see fig. 48-1). The posterior surface is grooved by (1) the mastoid process and the sternomastoid and digastric muscles and (2) more medially by the styloid process and its attached muscles. Medially, the superior part of the gland is pierced by the facial nerve and the inferior part by the external carotid artery.
The following structures lie partly within the parotid gland, from superficial to deep:
1. The facial nerve forms the parotid plexus within the gland and separates the glandular tissue partially into superficial and deep layers ("lobes"). In surgical excision of the parotid gland (e.g., for a tumor), damage to the facial nerve is a possibility.
2. The superficial temporal and maxillary veins unite in the gland to form the retromandibular vein, which contributes in a variable manner to the formation of the external jugular vein (see fig. 50-5).
3. The external carotid artery divides within the parotid gland into the superficial temporal and maxillary arteries.
The parotid duct, emerging under cover of the lateral surface, runs anteriorward on the masseter and turns medially to pierce the buccinator. The branching of the duct can be examined radiographically after injection of a radio-opaque medium (sialography, see fig. 48-4A). The parotid duct, which is palpable, opens into the oral cavity on the parotid papilla opposite the upper second molar tooth (see fig. 51-1A).
Innervation of parotid gland (see fig. 48-9).
Preganglionic parasympathetic secretomotor fibers (from the glossopharyngeal, tympanic, and lesser petrosal nerves) synapse in the otic ganglion. Postganglionic fibers travel with the auriculotemporal nerve and so reach the gland. Cranial nerves VII and IX communicate, so that secretory fibers to each of the three major salivary glands may travel in both the facial and glossopharyngeal nerves. The sympathetic supply to the salivary glands includes vasomotor fibers.
Superficial temporal artery (see fig. 48-1)
The superficial temporal artery, the smaller terminal branch of the external carotid artery, arises in the parotid gland, posterior to the neck of the mandible. Accompanied by the auriculotemporal nerve, it crosses the zygomatic arch and divides into frontal and parietal branches. Pulsations of the artery can be felt against the zygomatic arch. The transverse facial artery arises from the superficial temporal artery within the parotid gland and runs anteriorward inferior to the zygomatic arch.
Temporal and infratemporal fossae (fig. 48-3)
The temporal fossa is bounded by the temporal line, the frontal process of the zygomatic bone, and the zygomatic arch. Deep to the arch it communicates with the infratemporal fossa. The infratemporal fossa is bounded anteriorly by the posterior maxilla, superiorly by the infratemporal surface of the greater wing of the sphenoid bone (see fig. 42-12), medially by the lateral pterygoid plate (see fig. 42-11), and laterally by the ramus of the mandible. The temporalis is largely in the temporal fossa; the infratemporal fossa contains the two pterygoid muscles, the maxillary artery and the pterygoid venous plexus, and the mandibular nerve and chorda tympani.
Muscles of mastication (fig. 48-3)
The muscles of mastication are the masseter, temporalis, medial pterygoid and lateral pterygoid. They are all supplied by the mandibular nerve, a division of the trigeminal nerve (CN V). The muscles are summarized in table 48-1.
The masseter (fig. 48-3F) is conveniently described with the infratemporal region, although it is lateral to the ramus of the mandible. It is a quadrate muscle that can be divided partially into superficial, middle, and deep portions. The masseteric nerve from the anterior trunk of the mandibular nerve reaches the muscle by traversing the mandibular notch. The masseter is a powerful elevator of the mandible, and it can be palpated during clenching of the teeth.
The temporalis (fig. 48-3E) is fan-shaped and arises from the deep surface of the temporal fascia as well as from the floor of the temporal fossa. Its tendon passes deep to the zygomatic arch to reach the coronoid process of the mandible. It is supplied by deep temporal branches of the anterior trunk of the mandibular nerve. The temporalis maintains mandibular posture and elevates the mandible in molar occlusion. Its posterior fibers pull the head of the mandible posteriorward into the mandibular fossa during closure of the mouth.
The medial pterygoid muscle (fig. 48-3B) lies on the medial aspect of the ramus of the mandible. The lateral pterygoid muscle (fig. 48-3D) occupies the infratemporal fossa. The pterygoid muscles have two heads of origin each, and the two heads of the medial pterygoid embrace the lower head of the lateral pterygoid. The lateral and medial pterygoid muscles, acting together, protrude the mandible. The lateral pterygoid controls the articular disc, to which it is attached.
The temporomandibular joint is a synovial joint between (1) the articular tubercle, mandibular fossa, and postglenoid tubercle of the temporal bone on the superior side and (2) the head of the mandible on the inferior side. The articular surfaces are covered with fibrous tissue. The joint is immediatly anterior to the parotid gland, auriculotemporal nerve, and superficial temporal vessels. The articular capsule is loose but is strengthened laterally by a lateral ligament.
The articular disc, which is mostly fibrous, divides the joint into two separate compartments. Both the capsule and the disc receive a part of the insertion of the lateral pterygoid muscle which pulls them anteriorward during jaw opening. A separate synovial membrane is present peripherally in each of the two compartments of the joint.
The sphenomandibular ligament, from the spine of the sphenoid bone to the lingula of the mandible, lies medial to the joint. It is believed to develop from the sheath of the cartilage of the first pharyngeal arch. A fascial thickening between the styloid process and the angle of the mandible constitutes the stylomandibular ligament.
The temporomandibular joint is supplied by branches of the mandibular nerve (such as the auriculotemporal nerve) and by the terminal divisions of the external carotid artery.
Movements of the mandible (fig. 48-4).
The movements of the mandible are controlled largely by the action of muscles. Depression is produced by the lateral pterygoid and digastric muscles and by gravity. Elevation is due to the temporalis, masseter, and medial pterygoid muscle. Protrusion is caused by the pterygoid muscles and the masseter. Retraction results from the posterior fibers of the temporalis. Lateral movements depend on an interaction between all the muscles of mastication.
Anterior dislocation may result when the mouth is open: the head of the mandible may slip anteriorward off the articular tubercle. Reduction is accomplished by depressing the posterior jaw and elevating the chin.
The maxillary artery, the larger terminal branch of the external carotid artery, arises in the parotid gland, posterior to the neck of the mandible. It supplies the upper and lower jaws, the muscles of mastication, the palate, and the nose. Its course is described in three parts.
1. The mandibular part runs anteriorward medial to the neck of the mandible.
2. The pterygoid part runs anterosuperiorward under cover of the temporalis and either superficial or deep (see fig. 48-3D) to the inferior head of the lateral pterygoid muscle. Most branches of the first and second parts accompany branches of the mandibular nerve.
3. The pterygopalatine part passes between the heads of the lateral pterygoid muscle and then through the pterygomaxillary fissure into the pterygopalatine fossa. The branches of the third part accompany branches of the maxillary nerve and pterygopalatine ganglion.
The first part of the maxillary artery gives branches to the tympanic membrane, dura, and lower teeth. The middle meningeal artery is clinically the most important branch of the maxillary artery (see fig. 48-3C). It ascends posterior to the mandibular nerve and enters the cranial cavity through the foramen spinosum. The inferior alveolar artery accompanies the corresponding nerve, enters the mandibular foramen and canal, and supplies mucosa and lower teeth.
The second part of the maxillary artery supplies the muscles of mastication by deep temporal, pterygoid, masseteric, and buccal arteries.
The third part of the maxillary artery supplies the upper teeth, face, orbit, palate, and nasal cavity. The chief branches are several superior alveolar arteries, the infra-orbital and descending palatine arteries, the artery of the pterygoid canal, and the sphenopalatine artery. The sphenopalatine artery is the termination of the maxillary artery. It enters the nasal cavity through the sphenopalatine foramen, supplies the nose and paranasal sinuses. This aretery is the cause of the most serious, posterior nosebleeds (epistaxis).
Maxillary nerve (fig. 48-6)
The maxillary nerve (second division of the trigeminal nerve, V2) arises from the trigeminal ganglion, traverses the foramen rotundum, and enters the pterygopalatine fossa (where it can be "blocked" by passing a needle through the mandibular notch and injecting a local anesthetic). Then, as the infra-orbital nerve, it enters the orbit through the inferior orbital fissure and ends on the face by emerging from the infra-orbital foramen. The area of skin supplied by the maxillary nerve is tested by the use of cotton wool and a pin (see fig. 47-6).
Communications with the pterygopalatine ganglion enable the ganglion to distribute maxillary fibers. Posterior superior alveolar branches enter the maxilla and supply the molars and premolars and their gums. The zygomatic nerve enters the orbit through the inferior orbital fissure and divides into zygomaticotemporal and zygomaticofacial branches that end on the temple and face, respectively. A communication with the lacrimal nerve enables secretory fibers to reach the lacrimal gland (fig. 48-7). The infraorbital nerve is the continuation of the maxillary nerve. It traverses the inferior orbital fissure and occupies the infra-orbital groove, canal, and foramen. It ends on the face as inferior palpebral (to the lower eyelid), nasal (to the skin of the nose), and superior labial branches (to the mucosa). The infra-orbital nerve gives off a middle superior alveolar branch, which runs in the wall of the maxillary sinus, and an anterior superior alveolar branch, which descends sinuously in the front wall of the maxillary sinus and supplies the canine and incisors. The various superior alveolar nerves form a superior dental plexus within the maxilla. The branches of the maxillary nerve are listed in table 48-2.
Pterygopalatine ganglion (fig. 48-7)
The pterygopalatine ganglion is in the pterygopalatine fossa, inferior to the maxillary nerve and lateral to the sphenopalatine foramen. It can be injected with anesthetic by passing a needle through the mandibular notch and the pterygomaxillary fissure. A parasympathetic root from the greater petrosal nerve and the nerve of the pterygoid canal conveys preganglionic fibers from the facial nerve. These synapse in the ganglion, and the postganglionic fibers pass to the lacrimal gland(by the maxillary, zygomatic, and lacrimal nerves). A sympathetic root contains postganglionic fibers that traverse the ganglion without synapsing. An afferent root connects the ganglion with the maxillary nerve. These fibers come from the orbit, nasal cavity, palate, and nasopharynx by way of the so-called branches of the ganglion, which are mostly fibers of the maxillary nerve.
The mandibular nerve (third division of the trigeminal nerve, V3) arises from the trigeminal ganglion and, together with the motor root of the trigeminal nerve, traverses the foramen ovale and enters the infratemporal fossa (where it can be "blocked" by passing a needle through the mandibular notch and injecting a local anesthetic). At the base of the skull, the mandibular nerve is joined by the motor root and then divides into branches classified as anterior and posterior divisions. The area of skin supplied by the mandibular nerve is tested by the use of cotton wool and a pin (see fig. 47-6). The muscles of mastication are tested by palpating the temporalis and masseter on clenching of the teeth.
The trunk of the mandibular nerve gives off (1) a meningeal branch, the nervus spinosus, which accompanies the middle meningeal artery, and (2) the nerve to the medial pterygoid, which may also supply the tensor tympani and tensor veli palatini by way of the otic ganglion.
The anterior division of the mandibular nerve comprises several small branches, namely the buccal nerve (which emerges between the heads of the lateral pterygoid muscle and descends to supply sensory fibers to the skin and mucosa of the cheek, the gums, and perhaps the first two molars and premolars), the masseteric nerve (which traverses the mandibular notch to supply the masseter), deep temporal nerves (to the temporalis), and the nerve to the lateral pterygoid muscle.
The posterior division of the mandibular nerve, which is chiefly sensory, gives off the auriculotemporal nerve and divides into the lingual and inferior alveolar nerves.
The auriculotemporal nerve, which usually arises by two roots that encircle the middle meningeal artery, proceeds posteriorward deep to the neck of the mandible and closely related to the parotid gland (which it supplies).* The auriculotemporal nerve ascends posterior to the temporomandibular joint (which it supplies). It is accompanied by the superficial temporal artery, and both supply the scalp. The auriculotemporal nerve receives communications from the otic ganglion, conveying secretory fibers from the glossopharyngeal nerve to the parotid gland. Pain from disease of a tooth or the tongue is sometimes referred to the distribution of the auriculotemporal nerve to the ear.
The lingual nerve descends medial to the lateral pterygoid muscle and is joined by the chorda tympani (a branch of the facial nerve that contains taste fibers). The lingual nerve (which lies anterior to the inferior alveolar nerve) passes between the medial pterygoid muscle and the ramus of the mandible. It then lies under cover of the oral mucosa, where it is palpable posteroinferior to the third molar. It crosses the lateral surface of the hyoglossus, passes deep to the mylohyoid muscle, crosses the submandibular duct, and curves upward on the genioglossus. It gives several small branches (e.g., to the submandibular gland) and supplies sensory fibers to the anterior tongue, gums, and first molar and premolar.
The inferior alveolar nerve, with its companion artery, descends deep to the lateral pterygoid muscle and then enters the mandibular foramen and canal. Superior to the mandibular foramen, the inferior alveolar nerve can be "blocked" intra-orally with a local anesthetic. The inferior alveolar nerve gives off the mylohyoid nerve (which descends in a groove on the ramus of the mandible and supplies the mylohyoid muscle and the anterior belly of the digastric muscle), inferior dental branches (which form the inferior dental plexus and supply the lower teeth), gingival branches (to the gums), the mental nerve (which emerges through the mental foramen to supply skin), and the incisive branch, which is the termination and supplies the canines (sometimes) and incisors, including frequently the incisors of the opposite side.
Otic ganglion (fig. 48-9)
The otic ganglion is in the infratemporal fossa, immediately inferior to the foramen ovale and medial to the mandibular nerve. The parasympathetic root is the lesser petrosal nerve. These preganglionic fibers (from the glossopharyngeal nerve) synapse in the ganglion, and the postganglionic fibers pass to the auriculotemporal nerve, through which they supply the parotid gland. A sympathetic root (from the plexus on the middle meningeal artery) contains postganglionic fibers that traverse the ganglion without synapsing. An efferent root from the nerve to the medial pterygoid muscle is believed to supply the tensor tympani and tensor veli palatini. Some taste fibers from the tongue may also pass through the ganglion.
The trigeminal nerve is sensory from the face, anterior half of the scalp, teeth, mouth, nasal cavity, and paranasal sinuses, and motor to the muscles of mastication. It is attached to the side of the pons by a sensory and a motor root. The sensory root expands into the trigeminal ganglion, which gives rise to three large divisions: the ophthalmic (V1), maxillary (V2), and mandibular (V3). The motor root, which also contains afferent fibers from the muscles of mastication, joins the mandibular division. The attachment of the trigeminal roots to the pons is in an area termed the cerebellopontine angle. In this vicinity, space-occupying lesions (e.g., tumors) generally involve several or all of the local nerves, namely, the trigeminal, facial, and vestibulocochlear, and sometimes the glossopharyngeal and vagus also.
The branches of the trigeminal nerve are summarized in figure 48-10 and in table 48-3. The ophthalmic nerve (first division) runs anteriorward in the dura of the lateral wall of the cavernous sinus and divides into lacrimal, frontal, and nasociliary nerves, which enter the orbit through the superior orbital fissure. The nasociliary nerve is the afferent limb of the corneal reflex; the efferent limb is the facial nerve. The maxillary nerve (second division) lies in the dura lateral to the cavernous sinus. It passes through the foramen rotundum and enters the pterygopalatine fossa. Then, as the infra-orbital nerve, it enters the orbit through the inferior orbital fissure and ends on the face by emerging through the infra-orbital foramen. The mandibular nerve (third division), together with the motor root, passes through the foramen ovale to the infratemporal fossa. As it does so, it is joined by the motor root and thereupon divides into branches that are classified into an anterior and a posterior division.
Sarnat, B. G., and Laskin, D. M. (eds.), The Temporomandibular Joint. A Biological Basis for Clinical Practice, 3rd ed., Thomas, Springfield, Illinois, 1980. Detailed chapters on anatomy, physiology, pathology, diagnosis, and other topics.
48-1 What is "the hostage of parotid surgery?"
48-2 Where do the temporal and infratemporal fossae communicate?
48-3 Which muscles of mastication have at least two heads?
48-4 Which nerve supplies the muscles of mastication?
48-5 Which major part of the temporal bone takes part in the temporomandibular joint?
48-6 What is the significance of the sphenomandibular ligament?
48-7 Which muscles produce retraction of the mandible?
48-8 How is dislocation of the temporomandibular joint reduced?
48-9 Which is clinically the most important branch of the maxillary artery?
48-10 From which structures may pain be referred to the distribution of the auriculotemporal nerve?
48-11 What is the source of the afferent fibers that converge on the pterygopalatine ganglion?
48-12 What is the fundamental nature of the ganglia associated with the trigeminal nerve?
* The two roots of the auriculotemporal nerve usually enclose a V-shaped interval for the middle meningeal artery and then form a short trunk which breaks up into a spray of branches: two of these are communications with the facial nerve (J. J. Baumel, J. P. Vanderheiden, and J. E. McElenney, Am. J. Anat., 130:431-440, 1971).
Figure 48-1 The main salivary glands and their ducts: parotid, submandibular, and sublingual. The accessory parotid gland lies above the parotid duct. The chief branches of the facial nerve are shown, but the details of the parotid plexus have been omitted. For submandibular and sublingual glands, see also fig. 49-1.
Figure 48-2 A, The parotid gland, lateral aspect, sectioned horizontally to show the surfaces. B, Horizontal section at the level of the atlas. (B is based on Truex and Kellner and on Parsons.)
Figure 48-3 Six successively more superficial planes in the infratemporal region. A, Medial wall of infratemporal fossa (cf. fig. 42-11). B, Medial pterygoid muscle. C, Mandibular nerve and maxillary artery. Note the chorda tympani and the middle meningeal artery. D, lateral pterygoid muscle. The second part ofthe maxillary artery may be deep (as shown here) or superficial to the lower head of the lateral pterygoid muscle. The buccal nerve emerges between the heads of the lateral pterygoid. The masseteric nerve emerges above the upper head of the lateral pterygoid. E, Temporalis. The anterior fibers are attached to the ramus of the mandible. F, Masseter. The deep fibers (visible above) proceed directly inferiorward.
Figure 48-4 A, Parotid sialogram in vivo. Iodized oil has been injected through the parotid duct. B and C, The temporomandibular joint with the mouth closed (head in the mandibular fossa) and with the mouth open (head on the articular tubercle). The black oval area posterior to the head of the mandible is the external acoustic meatus. (Courtesy of Mr. John A. Hill, Birkenhead, England.)
Figure 48-5 The temporomandibular joint. A, lateral aspect. B, After partial removal of the capsule. C, Medial aspect. D, Superior aspect of the condylar process of the mandible and inferior aspect of the mandibular fossa and articular tubercle. Note the attachment of the capsule in both drawings. (After Sicher and Tandler.)
Figure 48-6 The maxillary nerve, lateral aspect.
Figure 48-7 The pterygopalatine ganglion and its connections, lateral aspect.
Figure 48-8 The mandibular nerve, lateral aspect.
Figure 48-9 The otic ganglion and its connections, lateral aspect. Interrupted lines, parasympathetic fibers. Continuous lines, sympathetic fibers. Red lines, motor fibers.