Anatomy of the Head: Parotid, Temporal, Infratemporal
HEAD: PAROTID, TEMPORAL, INFRATEMPORAL
Temporal Fossa
§ The temporal fossa is a depression in the lateral skull.
§ It is bordered by the superior temporal line, which is the site of attachment for the fascia investing the temporalis muscle.
§ The area bounded by the inferior temporal line is the site of attachment of the temporalis muscle itself.
§ Four cranial bones articulate in this fossa: temporal, parietal, frontal and sphenoid.
§ They converge at an “H-shaped” landmark called the pterion.
§ The pterion is a useful landmark for a structure located inside the cranium, the middle meningeal artery.
Clinical Correlate:
§ The bone of calvarium is thinnest in the temporal fossa. Strong blows to the side of the head may cause a depressed fracture, in which a fragment of bone is depressed inward to compress or injure the brain. At the pterion, the middle meningeal artery is easily ruptured following such an injury. The resulting hematoma will compress the brain and could be fatal if untreated. This region is also vulnerable to contrecoup fractures, in which fractures are contralateral to the site of the brain injury.
Infratemporal Fossa and Parotid Bed
§ The infratemporal fossa (colored blue) is bordered by several cranial bones.
The mandible (not shown) forms the lateral wall.
The maxilla forms the anterior wall.
The sphenoid bone forms most of the medial wall.
The sphenoid and temporal bones form the roof.
There is no posterior wall, but the fossa extends posteriorly as far as the mandibular fossa, where the mandible articulates with the cranium.
§ The infratemporal fossa communicates with the temporal fossa through the zygomatic arch.
§ The parotid bed (colored pink)
poorly defined area posterior to the infratemporal fossa
from the mandibular fossa to the mastoid process.
Temporomandibular Joint
§ The temporomandibular joint (TMJ) is the articulation between the mandible and the temporal bone.
§ The mandible
a single bone with several named parts: body, angle and ramus.
§ The ramus
splits to form an anterior coronoid process and a condylar process, which forms the TMJ.
§ The condylar process
sits in the mandibular process of the temporal bone.
§ In the joint, the two bones are separated by an articular disk
which in turn is cushioned by two synovial sacs.
The mandible is held in place by its connective tissue capsule and several ligaments
§ the lateral temporomandibular ligament
§ the stylomandibular ligament
§ the sphenomandibular ligament.
The TMJ supports several movements of the mandible.
§ The major movements are elevation/depression and protraction/retraction.
§ Small lateral or twisting movements useful in chewing are also permitted.
The muscles that support these movements are collectively called the muscles of mastication.
§ The temporalis muscle has a fan shape with fibers of different orientation.
The anterior, vertical fibers primarily produce elevation
The inferior, horizontal fibers primarily produce retraction.
§ The masseter muscle
produces elevation.
§ The medial pterygoid muscle
oriented parallel to the masseter
produces elevation of the mandible.
§ The lateral pterygoid muscle
protracts the mandible.
Counter-acts temporalis m. and masseter m.
Clinical Correlates
§ The mandible is relatively easily fractured by strong blows, as might occur during a fall. Because of the U-shape, a blow to one side will frequently produce a second fracture on the contralateral side. The neck of the mandible is particularly vulnerable due to the capsule of the TMJ, which restrains movement of the head. In contrast, fractures of the coronoid process are uncommon. Fractures of the neck frequently involve a dislocation of the TMJ as well. Fractures of the body and angle of the mandible may be accompanied by fractures of teeth.
§ A key functional property of the TMJ is its intrinsic mobility. Extreme movement, however, results in dislocation. In particular, when the mandible is depressed, the head is at the peak of the articular tubercle, and has no bony support. Excessive contraction of the lateral pterygoids, such as during a yawn or a large bite, may cause anterior dislocation. Similarly, when the mandible is depressed, a strong blow can easily dislocate the TMJ. Once the head passes anterior to the tubercle, the actions of most muscles of mastication will reinforce the dislocation. Therefore, it may be necessary to administer a muscle relaxant before reduction. Posterior dislocation is uncommon due to the structure of the postglenoid tubercle and the supporting ligaments.
§ One common problem is clicking (crepitus) of the TMJ on elevation and depression of the mandible. This appears to be due to abnormalities of the articular disk. Problems in TMJ function have been associated with a number of maladies, particularly headaches and toothaches, but insurance companies tend not to reimburse for this treatment strategy.
Arterial Supply
§ The blood supply to the lateral part of the skull is through the terminal branches of the external carotid artery.
§ The superficial temporal artery
supplies the skin over the lateral skull.
The maxillary artery
supplies the temporalis muscle itself and the infratemporal fossa.
There are three parts to this artery.
§ The mandibular part
lies lateral to the lateral pterygoid muscle
gives off the middle meningeal, inferior alveolar, anterior tympanic and deep auricular arteries.
§ The pterygoid part
crosses the lateral pterygoid muscle
gives off several muscular branches: deep temporal (usually two), masseter, pterygoid and buccal arteries.
§ The sphenopalatine part
lies medial to the lateral pterygoid muscle
essentially represents the bifurcation of the maxillary artery into its terminal branches, the sphenoplatine and infraorbital arteries.
The sphenopalatine artery gives off branches to the palate,and the infraorbital artery supplies the inferior orbit and face.
Clinical Correlate:
§ The pulse of the superficial temporal artery can be palpated as the artery crosses the root of the zygomatic process of the temporal bone, just anterior to the auricle. This pulse is relatively weak compared to the carotid or radial pulses, but is useful when these other sites are inaccessible. For example, an anesthesiologist at the head of an operating table may measure the temporal pulse when the rest of the body is draped.
Venous Drainage
§ Veins do not have valves
§ In general, veins parallel the arteries, draining into both external and internal jugular veins.
§ The most consistent of these are the superficial temporal and maxillary veins
which join to form the retromandibular vein.
§ The pterygoid venous plexus is of clinical importance.
It lies lateral to the maxillary artery and drains to the maxillary vein and to the deep facial vein.
It also anastomoses with the cavernous sinus inside the cranium through communicating veins.
Clinical Correlate:
§ Anastomoses of the pterygoid venous plexus with the facial vein and cavernous sinus represent an important potential pathway for the spread of infection. Normally, blood from the medial angle of the eye, nose and lips drains down through the facial vein. Veins in the head, including those of the pterygoid venous plexus, do not have valves, however. Infections may therefore reverse the flow of blood into the cavernous sinus, resulting ultimately in meningeal infections.
Parotid Gland
§ Like the submandibular gland, the parotid gland secretes saliva into the oral cavity.
§ Fluid is carried to the oral cavity through the parotid duct.
The parotid duct opens to the oral cavity at the second upper molar.
§ An accessory parotid gland may be present.
It lies anteriorly over the masseter muscle, between the parotid duct and zygomatic arch. Its ducts connect directly to the parotid duct.
§ The parotid gland is important anatomically because of the large number of important structures that are embedded within it.
Include: the external carotoid artery, the maxillary artery (not shown), the retromandibular vein, the facial nerve and the auriculotemporal nerve
Clinical Correlates:
§ Viral infection of the parotid gland (mumps) results in swelling and inflammation. Because of the tight capsule surrounding the gland (paratidomassateric fascia), this is a painful condition. Pain may be referred to the auricle, external acoustic meatus, temporal region and TMJ due to stimulation of the auriculotemporal nerve, which passes through and innervates the parotid. Bacterial infection of the parotid gland produces an abscess, a localized region of inflammation that acts as a space-filling lesion. Parotid abscesses must be differentiated from dental abscesses, both of which may produce swelling of the cheek.
§ The duct system of the parotid gland can be visualized radiographically by injection of a contrast dye through the parotid papilla. This technique can reveal portions of the duct system that are blocked, displaced or dilated by disease. Blockage of the duct is most commonly due to formation of a calcified deposit. Stimulation of secretion from the gland can be painful due to dilation of the proximal portion of the duct.
Nerve Supply
§ Several cranial nerves innervate structures in the temporal and infratemporal fossae.
§ In addition, there are several important relationships among different cranial nerves that occur in this region.
§ Cranial nerve V
major source of innervation to the lateral skull.
It provides general sensory innervation to skin overlying the fossae via its second and third divisions (CN V2 and CN V3).
The major sensory branches are the inferior alveolar, lingual, auriculotemporal and buccal nerves.
§ CN V3
also provides branchial motor innervation to muscles of mastication.
Branches of CN V3 can be found in characteristic relationships to pterygoid muscles.
§ The buccal nerve
emerges between two heads of the lateral pterygoid muscle.
Sensory n. to cheek
§ The chorda tympani (CN VII)
joins the lingual nerve deep to the lateral pterygoid muscle.
§ The lingual and inferior alveolar nerves
emerge between the lateral and medial pterygoid muscles.
§ Cranial nerve VII
passes through the infratemporal fossa.
Its chorda tympani branch provides special sensory fibers to tongue via CN V3.
CN VII also provides visceral motor fibers to the lacrimal gland via CN V2 and to salivary glands via CN V3.
§ Cranial nerve IX
provides visceral motor innervation of the parotid gland via the auriculotemporal nerve (CN V3).
The pathways by which CN V distributes fibers from CN VII and CN IX to their target tissues are described in greater detail below:
1. Special sensory fibers from CN VII branch off from the main trunk as the chorda tympani–>middle ear–>joins the lingual n. in the infratemporal fossa–>anterior 2/3 of the tongue.
2. Preganglionic parasympathetic fibers from CN VII branch off from the geniculate ganglion as the greater petrosal n.–>nerve of the pterygoid canal–>sphenopalatine ganglion:
a. sphenopalatine ganglion–>postganglionic fibers–>CN V2–>zygomaticotemporal n.–>lacrimal n. (CN V1) in the orbit–>lacrimal gland
b. sphenopalatine ganglion–>postganglionic fibers–>branches of CN V2–>mucous glands of nasal and oral cavities
3. Preganglionic parasympathetic fibers from CN VII follow the chorda tympani to the lingual nerve (as described above), but –> submandibular ganglion –> postganglionic fibers –> lingual n. –>submandibular and sublingual glands
4. Preganglionic parasympathetic fibers from CN IX branch from the inferior ganglion as the tympanic n. –> tympanic plexus –> lesser petrosal n. –> otic ganglion –> postganglionic fibers –> auriculotemporal n. –> parotid gland
Clinical Correlates:
§ The pathways described above are significant clinically because they help describe the consequences of interrupted nerve function, due either to anesthesia or injury. For example, the region of tissue to be anesthetized will determine the site of injection. To numb all branches of CN V3 (mandibular nerve), a needle is passed through the mandibular notch to the roof of the infratemporal fossa. To numb the mandibular teeth for a dental procedure, anesthetic is injected at the lingula of the mandible to block the inferior alveolar nerve. If the needle passes too far posteriorly, it may anesthetize branches of CN VII coursing through the parotid gland. The skin and mucous membrane of the lower lip, the gingivae, and the skin of the chin are also anesthetized because the mental nerve innervates them. To block just the mental nerve (e.g. to place a suture in the skin of the chin), anesthetic is injected into the mental foramen. To anesthetize the cheek, injection should be made into the mucosa covering the retromolar fossa, located posterior to the 3rd mandibular molar.
§ Lesions of branches of the trigeminal nerve, through penetrating injury, compression by tumor, etc., will follow a similar pattern. Especially informative is the interruption of autonomic function due to postganglionic parasympathetic fibers carried by branches of CN V.
§ Trigeminal neuralgia (tic douloureux) is a sensory disorder in which the patient experiences strong paroxysmal pain in regions innervated by the maxillary and mandibular branches of CN V. It is thought to be due to the presence of an anomalous artery that compresses the root of the nerve. Symptoms can frequently be alleviated by surgically moving the artery.
§ Branches of the facial nerve pass through the parotid bed and the gland itself, and are therefore subject to traumatic injury. Injury to the nerve distal to the stylomastoid foramen will paralyze muscles of facial expression, but not autonomic function or special sensation. Injury of CN VII within or anterior to the parotid gland will result in more circumscribed motor deficits.
Tags: Anastomoses, condylar process, crepitus, fascia, head, Infratemporal Fossa, lateral pterygoid muscle, mandible, masseter muscle, maxillary artery, paratidomassateric fascia, Parotid Bed, parotid duct, parotid papilla, pterion, pterygoid muscle, sphenoid, sphenomandibular ligament, sphenopalatine, stylomandibular ligament, superior temporal line, Temporal Fossa, Temporomandibular Joint, TMJ, Venous drainage, zygomatic arch
