2.4 The Infratemporal Fossa and Spread of Odontogenic Infection

The Infratemporal Fossa

The infratemporal fossa (ITF) is an irregularly shaped anatomical space situated deep to the ramus of the mandible and inferior to the greater wing of the sphenoid. It acts as an indispensable surgical crossroads through which neurovascular structures traverse between the cranium, face, and oral cavity.

Boundaries of the Infratemporal Fossa

• Superior (Roof): Infratemporal surface and crest of the greater wing of the sphenoid, and the squamous part of the temporal bone (pierced by the foramen ovale and foramen spinosum).
• Anterior: Infratemporal (posterior) surface of the body of the maxilla and the posterior aspect of the zygomatic bone (contains the alveolar foramina for the PSA nerves and vessels; separated superiorly from the orbit by the inferior orbital fissure).
• Medial: Lateral surface of the lateral pterygoid plate and the pyramidal process of the palatine bone; deeper, the tensor veli palatini, levator veli palatini, and superior pharyngeal constrictor.
• Lateral: Medial surface of the mandibular ramus and the coronoid process.
• Posterior: Styloid process, carotid sheath, and the tympanic plate of the temporal bone.
• Inferior: Open to the tissue spaces of the neck; continuous with the submandibular and parapharyngeal spaces at the level of the mandibular angle.

Contents of the Infratemporal Fossa

1. Muscular: Lower portion of the temporalis tendon inserting into the coronoid process; lateral and medial pterygoid muscles.
2. Neurological:
   • Mandibular nerve (CN V3) trunk and its anterior and posterior divisions.
   • Otic Ganglion: Parasympathetic ganglion located directly medial to the CN V3 trunk, just below the foramen ovale. Receives preganglionic parasympathetics from CN IX via the lesser petrosal nerve; postganglionic fibres join the auriculotemporal nerve to supply the parotid gland.
   • Chorda Tympani (CN VII): Enters the ITF through the petrotympanic fissure, runs downward and forward medial to the spine of the sphenoid and middle meningeal artery, and merges with the posterior border of the lingual nerve at an acute angle.
3. Vascular:
   • Maxillary Artery: The larger terminal branch of the external carotid artery (arising within the parotid gland at the condylar neck). It courses through the infratemporal fossa, divided into three anatomical parts by its relationship to the lateral pterygoid muscle:
     • First (Mandibular) Part: Runs horizontally forward between condylar neck and sphenomandibular ligament. Gives off the deep auricular, anterior tympanic, middle meningeal (ascends vertically through foramen spinosum into cranium), accessory meningeal (enters foramen ovale), and inferior alveolar artery (enters mandibular foramen with IAN).
     • Second (Pterygoid) Part: Runs obliquely anterosuperiorly either superficial (60%) or deep (40%) to the lower head of the lateral pterygoid. Gives off muscular branches: deep temporal, pterygoid, masseteric, and buccal arteries.
     • Third (Pterygopalatine) Part: Passes through the pterygomaxillary fissure into the pterygopalatine fossa. Gives off the posterior superior alveolar, infraorbital, greater palatine, pharyngeal, artery of the pterygoid canal, and terminates as the sphenopalatine artery.
   • Pterygoid Venous Plexus: An extensive, highly anastomotic network of veins located around and within the lateral and medial pterygoid muscles. Drains the territories supplied by the maxillary artery, converging into the maxillary vein, which merges with the superficial temporal vein to form the retromandibular vein.

[!IMPORTANT] Clinical Traps & Spread of Odontogenic Infection:

• Cavernous Sinus Thrombosis: The pterygoid venous plexus communicates with the facial vein via the deep facial vein, and critically, with the intracranial cavernous sinus via emissary veins traversing the foramen ovale and foramen lacerum. Because these veins are entirely valveless, retrograde blood flow can transport septic emboli from an infected maxillary molar or deep fascial space cellulitis directly into the cavernous sinus, precipitating life-threatening cavernous sinus thrombosis (manifesting with periorbital oedema, proptosis, chemosis, and palsies of CN III, IV, VI, and V1/V2).
• PSA Block Haematoma: An improperly angled posterior superior alveolar block needle that is angled too far posteriorly or penetrates deeper than 16 mm can lacerate the pterygoid venous plexus or the maxillary artery. Venous bleeding causes rapid, painless swelling of the cheek within minutes, transforming into an extensive visible purple ecchymosis over the subsequent 48 hours.

Why This Fossa Matters for Spreading Infection

Infection reaching the infratemporal fossa gains access to the pterygoid venous plexus, which communicates with the cavernous sinus through emissary veins and with the facial vein through the deep facial vein. Because these veins are valveless, infection can travel against the direction of normal flow. That single anatomical fact underlies the classic teaching that infections of the midface are dangerous and must never be squeezed or incised in primary care.