L61. GA - Temporal Region & Infratemporal Fossa

• The temporal region and infratemporal (IT) fossa are clinically important due to the presence of terminal branches of the external carotid artery and trigeminal nerve (CN V).
• An important branch of the facial nerve (CN VII) travels through the IT fossa and joins with a branch of V3.
• Muscles of mastication, which produce mandibular movements at the temporomandibular joint, are located in the temporal region and IT fossa.

Skeletal Framework of Temporal Region & IT Fossa

• The infratemporal crest marks the boundary between the temporal fossa and the infratemporal fossa.
• The IT fossa is posterior to the maxilla, inferior to the zygomatic arch, deep to the ramus of the mandible, and superficial to the lateral pterygoid plate of the sphenoid bone.
• The temporal fossa is posterior to the zygomatic bone, inferior to the parietal bone, contains the temporalis muscle, and is superficial to the squamous portion of the temporal bone.

Temporomandibular (TM) Joint

• The TM joint is a synovial joint where the mandibular head articulates with the mandibular fossa and articular tubercle.
• A fibrous capsule covers the TM joint, thickened laterally as the temporomandibular (lateral) ligament.
• The stylomandibular and sphenomandibular ligaments provide additional support to the joint.
• The TM joint has two chambers, divided by a fibrocartilaginous articular disc.
• The TM joint allows hinge-like rotation and forward gliding motions.
• When the mouth is closed, the mandibular head aligns vertically with the mandibular fossa.
• Initial mouth opening involves hinge rotation, while wider opening involves the mandibular head and articular disc gliding forward to the articular tubercle.
• TM joint dislocations occur when the mandibular head passes anterior to the articular tubercle, often due to yawning or trauma.
• Dislocation prevents complete mouth closure due to molar teeth contact; pain results, transmitted by the auriculotemporal nerve (V3 branch).

Muscles Acting on the Mandible

• Temporalis originates from the temporal fossa and fascia, inserting on the coronoid process and anterior border of the ramus.
• Masseter originates from the zygomatic arch and bone, inserting on the angle and lateral surface of the mandibular ramus.
• Lateral pterygoid originates from the greater wing of the sphenoid and lateral pterygoid plate, inserting on the neck of the mandible and the TM joint capsule.
• Medial pterygoid originates from the maxilla and lateral pterygoid plate, inserting on the medial surface of the mandible angle.
• Mandibular movements include protrusion, retraction, elevation, and depression.
• Protrusion is achieved by the lateral pterygoid, assisted by the medial pterygoid.
• Retraction is achieved by the posterior fibers of temporalis, the deep masseter, geniohyoid, and digastric muscles.
• Elevation occurs via the temporalis, masseter, and medial pterygoid.
• Depression is mainly due to gravity, assisted by suprahyoid muscles (digastric, mylohyoid, and geniohyoid) against resistance.
• Pterygoid muscles enable side-to-side movements during chewing, aided by the temporalis.
• All masticatory muscles are innervated by the mandibular division of the trigeminal nerve (CN V3).

Nerves of the Temporal Region & IT Fossa

• Within the cranial cavity, V3 is located in the middle cranial fossa, which then travels through the foramen ovale to enter the IT fossa.
• V3 has sensory and motor branches; larger branches in the IT fossa are sensory. Motor branches are smaller and located within the muscles.
• V3 motor branches innervate all four masticatory muscles, two suprahyoid muscles (mylohyoid and anterior digastric), one soft palate muscle (tensor veli palatini), and one middle ear muscle (tensor tympani).

V3 Sensory Branches

• Cell bodies are located in the trigeminal ganglia.
• The lingual nerve runs parallel and anterior to the inferior alveolar nerve, entering the mouth near the mandibular ramus and passing under the mucosa below the 3rd molar tooth; provides general sensation from anterior 2/3 of tongue, floor of mouth, & lower gingiva.
• The inferior alveolar nerve runs parallel and posterior to the lingual nerve, entering the mandibular foramen, sending branches to lower teeth, and exiting as the mental nerve in the chin region, providing general sensation from lower teeth, chin, & lower lip.
• The auriculotemporal nerve runs posteriorly toward the mandibular neck, relates to the middle meningeal artery, and provides general sensation from the temporal region, auricle, & TM joint.
• The buccal nerve runs between the heads of the lateral pterygoid muscle, emerges superficially toward the cheek region, and provides general sensation from cheek & lower gingiva.
• The nerve to the mylohyoid travels with the inferior alveolar nerve but does not enter the mandibular foramen rather runs on the medial surface of the mandible in the mylohyoid groove, innervating the mylohyoid and anterior digastric muscles.
• The chorda tympani nerve (CN VII branch) enters the IT fossa via the petrotympanic fissure, joins the lingual nerve, and travels with it into the floor of the mouth.
• Chorda tympani provides special sensation (taste) from anterior 2/3 tongue (cell bodies in geniculate ganglion) + preganglionic PANS fibers from CN VII to submandibular ganglion to stimulate submandibular & sublingual gland secretions

Autonomic Nerves

• Preganglionic parasympathetic (PANS) fibers travel through the IT fossa to reach ganglia with postganglionic PANS cell bodies
• Cell bodies of preganglionic PANS neurons are located in brainstem as part of CN VII (facial nerve)
• Preganglionic PANS axons travel into chorda tympani nerve, which joins lingual nerve within IT fossa
• PANS axons jump from the lingual nerve to innervate postganglionic PANS cell bodies of the submandibular ganglia
• Postganglionic PANS axons travel to submandibular and sublingual glands
• Lesser petrosal nerve (CN IX) enter the foramen ovale synapsing on the otic ganglion.
• Postganglionic PANS travel to the parotid gland via the auriculotemporal nerve.

Clinical Application: Effects of Nerve Injury

• Injury to the lingual nerve in the IT fossa distal to where it is joined by the chorda tympani nerve will produce a loss of general sensation (touch, pain) from the anterior 2/3 tongue, lower oral mucosa, and lower gingivae, PLUS a loss of taste sensation from the anterior 2/3 tongue affecting the 2 salivary glands (preganglionic PANS is lost).
• Injury to the lingual nerve in the IT fossa proximal to where it is joined by the chorda tympani nerve will only produce a loss of general sensation (touch, pain) from the anterior 2/3 tongue, lower oral mucosa, and lower gingivae.
• Damage to CN V in its entirety causes sensory loss in V1 V2 and V3 which leads to paralysis of all muscles innervated by V3 motor fibers + all muscles of mastication (ipsilateral).

Vasculature of the Temporal Region & IT Fossa

• The external carotid artery terminates by splitting into the maxillary and superficial temporal arteries.
• The superficial temporal artery gives off the transverse facial artery and continues superiorly to the lateral aspect of the scalp.
• The maxillary artery arises from the external carotid artery posterior to the neck of the mandible and travels anteriorly through the IT fossa.
• The Maxiallary artery is followed by many branches (Superficial Temporal, Middle Meningeal, Inferior Alveolar, Deep Temporal, Buccal.
• The superficial temporal vein drains the temporal (lateral) region of the scalp + a short maxillary vein to drain into the retromandibular vein.
• The pterygoid venous plexus is located between the medial & lateral pterygoid muscles and carries the structure from the IT fossa
• The pterygoid venous plexus connects to the cavernous sinus via emissary veins allowing peripheral infections from face, nasal & oral cavities to drain the sinus.

Approach to Dissection of IT Fossa

• Reflect the masseter muscle, parotid gland and duct, and branches of facial nerve.
• Clean the lateral surface of the ramus of the mandible.
• Cut the zygomatic arch and ramus of mandible as shown in Fig 19.

Overview of the temporal region and infratemporal fossa, including skeletal framework and the temporomandibular joint. Cranial nerves V and VII are discussed. Muscles of mastication are located in this region.