Chapter 21. Infratemporal Fossa

Big Picture

The infratemporal fossa is the region deep to the ramus of the mandible. The infratemporal fossa accommodates the insertion of the temporalis muscle, medial and lateral pterygoid muscles, mandibular nerve [cranial nerve (CN) V-3], otic ganglion, chorda tympani nerve, maxillary artery, and the pterygoid plexus of the veins.

Boundaries

The infratemporal fossa has the following boundaries (Figure 21-1A):

• Deep to the zygomatic arch.
• Anterior to the mastoid and styloid processes of the temporal bone.
• Posterior to the maxilla.
• Medial to the ramus of the mandible.
• Lateral to the pterygoid plate and the pterygomaxillary fissure, a communication between the infratemporal fossa and the pterygopalatine fossa.

Big Picture

The articulations between the temporal bone (mandibular fossa) and the mandibular condyle form a synovial joint, known as the temporomandibular joint (TMJ).

Movements of the TMJ

The left and right TMJ's work together, enabling the mandible to move as follows:

• Elevation (up). Generated by the temporalis, masseter, and medial pterygoid muscles.
• Depression (down). Generated by the digastricus, geniohyoid, and mylohyoid muscles, and assisted by gravity.
• Protraction. Generated primarily through the lateral pterygoid muscle. Involves the anterior movement of the mandibular condyle and the articular disc.
• Retraction. Generated by the geniohyoid, digastricus, and temporalis muscles.
• Side-to-side. Generated by the pterygoid muscles.

Structure of the TMJ

A unique feature of the TMJ is the fibrocartilaginous articular disc, located within the joint capsule between the mandibular fossa and condyle. The disc divides the joint capsule into two distinct compartments.

• Inferior compartment. Enables the hinge-like rotation of the mandibular condyle, corresponding to the first 2 cm of opening the mouth (depression) (Figure 21-1B).
• Superior compartment. For the mouth to be opened more than 2 cm, the superior compartment within the joint capsule enables both the mandibular condyle and the articular disc to slide anteriorly (protrusion), incorporating a translational movement anteriorly when opening the mouth wider (Figure 21-1C).

Muscle Movement of the TMJ

The muscles acting upon the TMJ are primarily the muscles that generate the various movements associated with chewing; hence, these muscles are often called the muscles of mastication (Table 21-1). The branchial motor division of CN V-3 innervates each of the following muscles (Figure 21-1D and E):

• Temporalis muscle. Originates in the temporal fossa and courses deep to the zygomatic arch, inserting in the infratemporal fossa on the coronoid process of the mandible. The temporalis muscle elevates the mandible.
• Masseter muscle. Attaches between the zygomatic arch and the external surface of the ramus of the mandible. It elevates the mandible. The masseter muscle is not located in the infratemporal fossa; however, because it works functionally with the temporalis and pterygoid muscles to move the mandible at the TMJ, it is a muscle of mastication.
• Lateral pterygoid muscle. Attaches between the lateral pterygoid plate and the mandibular condyle. Contraction causes the mandibular condyle and the articular disc to move anteriorly, resulting in both protraction and depression of the mandible. The lateral pterygoid muscle works synergistically with the medial pterygoid muscle to move the mandible from side to side.
• Medial pterygoid muscle. Attaches between the medial and lateral pterygoid plates and the internal surface of the ramus of the mandible. The medial pterygoid muscle elevates the mandible and moves it from side to side.

Big Picture

The trigeminal nerve (CN V) provides most of the general sensory innervation to the head. Branches of the ophthalmic nerve (CN V-1) and the maxillary nerve (CN V-2) provide only general sensory innervation. In contrast, CN V-3 enters the infratemporal fossa and has both a general sensory and a branchial motor root. Branches of the maxillary artery provide the vascular supply to the infratemporal fossa.

Innervation of the Infratemporal Fossa

The sensory and motor roots of CN V-3 fuse together as a trunk and descend into the infratemporal fossa via the foramen ovale (Figure 21-2A). Once in the infratemporal fossa, CN V-3 bifurcates into anterior and posterior divisions.

• Trunk. Provides branchial motor innervation via branches to the medial pterygoid, tensor veli palatine, and tensor tympani muscles.
• Anterior division
  • Motor branches. Provides branchial motor innervation via branches to the temporalis, masseter, and lateral pterygoid muscles.
  • Buccal nerve. Provides general sensory innervation from the skin of the cheek, passing between the two heads of the lateral pterygoid muscle. The buccal nerve is also referred to as the long buccal nerve to distinguish it from the buccal branch of CN VII.
• Posterior division
  • Auriculotemporal nerve. Splits around the middle meningeal artery to provide general sensory innervation to the temporal region of the face and scalp.
  • Otic ganglion. Preganglionic parasympathetic neurons from the glossopharyngeal nerve (CN IX) exit the middle ear as the lesser petrosal nerve and enter the infratemporal fossa through the foramen ovale and synapse in the otic ganglion. Postganglionic parasympathetic neurons “hitch-hike” along with the auriculotemporal nerve, providing visceral motor innervation to the parotid gland.
• Inferior alveolar nerve. Enters the mandibular foramen along with the inferior alveolar artery, providing general sensory innervation from the mandibular teeth the gingivae, lower lip, and chin.
• Lingual nerve. Provides general sensory innervation from the anterior two-thirds of the tongue (Figure 21-2A and B).
  • Chorda tympani nerve (CN VII). Enters the infratemporal fossa via the petrotympanic fissure, where it joins with the lingual nerve. The chorda tympani nerve provides special sensory taste from the anterior two-thirds of the tongue, as well as visceral motor parasympathetic innervation to the submandibular and sublingual salivary glands.
  • Submandibular ganglion. Suspended from the lingual nerve, where preganglionic and postganglionic parasympathetic neurons from the chorda tympani nerve (CN VII) synapse en route to providing visceral motor innervation to the submandibular and sublingual salivary glands.
• Nerve to the mylohyoid. Provides branchial motor innervation to the mylohyoid and anterior digastricus muscles.

Vascular Supply of the Intratemporal Fossa

The external carotid artery terminates as the maxillary artery and superficial temporal arteries, posterior to the neck of the mandible (Figure 21-2C). The maxillary artery courses medially and anteriorly to enter the infratemporal fossa. The maxillary artery disappears medially through the pterygomaxillary fissure into the pterygopalatine fossa as the sphenopalatine and infraorbital arteries in the nasal cavity and orbit, respectively. Although the maxillary artery gives off numerous branches, the two most important arteries are as follows:

• Middle meningeal artery. Ascends through the foramen spinosum, coursing between the roots of the auriculotemporal nerve. The middle meningeal artery provides the principal blood supply to the dura mater in the skull.
• Inferior alveolar artery. Joins the inferior alveolar nerve and enters the mandibular foramen.

The pterygoid plexus of veins is situated around the lateral pterygoid muscle. The pterygoid plexus communicates with veins in the orbit, cavernous sinus, and facial region.