Anatomy and surgical importance of infraremporal fossa 20 marks answer for ms ent exam

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Infratemporal Fossa: Anatomy and Surgical Importance

(20-mark answer for MS ENT examination)

Introduction

The infratemporal fossa (ITF) is a wedge-shaped, clinically vital deep space of the head located inferior to the temporal fossa and between the ramus of the mandible laterally and the pharyngeal wall medially. It is open to the neck posteroinferiorly. Its importance in ENT surgery lies in its complex neurovascular contents, its communications with surrounding spaces, and its involvement in both benign and malignant pathologies requiring skull base surgical approaches.

1. Boundaries

Borders of the Infratemporal Fossa - Gray's Anatomy for Students

Wall	Boundary
Roof (superior)	Inferior surfaces of the greater wing of sphenoid and squamous temporal bone; contains foramen ovale, foramen spinosum, and petrotympanic fissure; open superiorly to temporal fossa lateral to the infratemporal crest
Anterior	Posterior surface of the maxilla; upper part opens into orbit via inferior orbital fissure; contains alveolar foramen
Posterior	Mastoid and tympanic portions of temporal bone
Lateral	Medial surface of the ramus of mandible (contains opening of mandibular canal); zygomatic arch
Medial	Lateral pterygoid plate anteriorly; pharynx and tensor/levator veli palatini muscles posteriorly; contains the pterygomaxillary fissure (leading to pterygopalatine fossa)
Inferior	Open (continuous with the neck); superior limit of posterior belly of digastric and angle of mandible

2. Communications

The infratemporal fossa communicates with several adjacent spaces - these pathways are of major surgical and pathological importance:

Structure	Pathway
Orbit	Inferior orbital fissure
Middle cranial fossa	Foramen ovale and foramen spinosum
Pterygopalatine fossa	Pterygomaxillary fissure
Temporal fossa	Between zygomatic arch and cranium

Via its communications, the ITF provides surgical access to the cavernous sinus, sphenoid sinus, nasopharynx, petrous apex, clivus, and parasellar region.

3. Contents

A. Muscles

Lateral Pterygoid:

Two heads: superior (from roof/infratemporal crest of greater wing of sphenoid) and inferior (from lateral surface of lateral pterygoid plate)
Both portions insert onto the temporomandibular joint (articular disc and neck of condyle)
Action: Protrusion of mandible; depression when acting bilaterally; side-to-side chewing
Innervation: Nerve to lateral pterygoid (from V3)

Medial Pterygoid:

Deep head: from medial surface of lateral pterygoid plate and pyramidal process of palatine bone
Superficial head: from tuberosity of maxilla
Insertion: Roughened medial surface of angle and ramus of mandible
Action: Elevation and protrusion of mandible
Innervation: Nerve to medial pterygoid (from V3)

Also present: Lower fibres of temporalis inserting on the coronoid process pass through this space.

B. Nerves

Mandibular nerve (V3) - the most important nerve in the ITF:

Enters through foramen ovale
Divides into anterior (mainly motor) and posterior (mainly sensory) trunks
Motor branches: to all four muscles of mastication (masseter, temporalis, both pterygoids) + tensor tympani + tensor veli palatini
Sensory branches:
- Auriculotemporal nerve - carries secretomotor fibres to parotid (via otic ganglion); also sensory to TMJ, external auditory canal, and skin of temporal region
- Inferior alveolar nerve - enters mandibular foramen; gives off motor branch to mylohyoid; provides sensation to lower teeth and lower lip (mental nerve)
- Lingual nerve - sensory to anterior 2/3 of tongue; joined by chorda tympani in the fossa
- Buccal nerve - sensory to cheek mucosa

Chorda tympani (branch of CN VII):

Enters the ITF via the petrotympanic fissure
Passes vertically and medially to the lateral pterygoid to join the lingual nerve
Carries taste from anterior 2/3 of tongue and preganglionic parasympathetic secretomotor fibres to submandibular and sublingual glands
Surgical importance: At risk during TMJ surgery, parotid approaches, and infratemporal dissections

Otic Ganglion:

Lies medial to V3 just below foramen ovale
Preganglionic parasympathetic input: lesser petrosal nerve (CN IX)
Postganglionic fibres carried by the auriculotemporal nerve to the parotid gland
Sympathetic input: from plexus on middle meningeal artery

Lesser petrosal nerve:

From tympanic branch of CN IX (Jacobson's nerve)
Passes through the middle ear and exits foramen ovale/small canal to reach the otic ganglion

C. Arteries

Maxillary artery (internal maxillary artery):

Terminal branch of the external carotid artery
Arises posterior to the neck of the mandible
Passes lateral to the lateral pterygoid muscle into the ITF
Courses anterior to the pterygomaxillary fissure and enters the pterygopalatine fossa
Three parts/portions with branches:

Part	Location	Key Branches
1st (mandibular)	Behind neck of mandible	Deep auricular, anterior tympanic, middle meningeal, accessory meningeal, inferior alveolar
2nd (pterygoid)	Superficial/deep to lateral pterygoid	Deep temporal (anterior & posterior), pterygoid branches, masseteric, buccal
3rd (pterygopalatine)	Pterygopalatine fossa	Posterior superior alveolar, infraorbital, descending palatine, artery of pterygoid canal, sphenopalatine

Middle meningeal artery - enters foramen spinosum; of critical surgical importance (epidural haematoma)

D. Veins

Pterygoid venous plexus:

Dense network of veins surrounding the lateral pterygoid muscle
Drains posteriorly into the maxillary vein (to retromandibular vein) and anteriorly into the facial vein
Anastomoses with: cavernous sinus (via emissary veins through foramen ovale/spinosum), ophthalmic veins, pharyngeal venous plexus
Surgical/clinical significance: Infection in the ITF can spread haematogenously via this plexus to the orbit (orbital cellulitis) and to the cavernous sinus (cavernous sinus thrombosis), with potentially fatal consequences

4. Pathology Involving the Infratemporal Fossa

The following conditions primarily involve or spread to the ITF in ENT practice:

Juvenile nasopharyngeal angiofibroma (JNA) - Stage III/IV disease extends to the ITF (Andrews/Sessions staging)
Deep lobe parotid tumours - extend medially into the prestyloid parapharyngeal/ITF space
Glomus jugulare tumours - extend inferiorly into the ITF
Nasopharyngeal carcinoma - lateral extension to the ITF via the sinus of Morgagni
Maxillary sinus carcinoma (T4) - posterior extension into the ITF
Cholesteatoma / petrous apex disease - surgical access via ITF approaches
Trigeminal neuralgia - ITF is the approach zone for V3 block and percutaneous procedures
Mandibular nerve block - performed in the ITF for lower dental anaesthesia

5. Surgical Importance and Approaches

Fisch Infratemporal Fossa Approaches

Ugo Fisch developed the landmark lateral skull base approaches to the ITF, classified as Types A, B, and C:

Type A (Postauricular - Access to temporal bone/jugular foramen)

Indications:

Glomus jugulare/tympanicum tumours
Squamous cell carcinoma of temporal bone
Salivary gland cancers
Cholesteatoma with complications
Neurinoma (schwannoma) of jugular foramen
Meningioma, rhabdomyosarcoma

Key steps:

Large C-shaped postauricular incision extending into temporal scalp and into the neck
Flap elevation superficial to temporalis, SCM, and postauricular muscles
EAC transected at bony-cartilaginous junction; meatal skin everted and closed
Anteriorly based mastoid periosteal flap reinforces closed EAC
Radical mastoidectomy - removal of osseous EAC, all air cells lateral to otic capsule
Stapes suprastructure removed; Eustachian tube obliterated
Facial nerve skeletonised from geniculate ganglion to stylomastoid foramen and anteriorly translocated
Mastoid tip removed; SCM detached
Cervical dissection exposing CN IX, X, XI, XII, internal carotid artery, internal jugular vein
Internal carotid artery dissected from neck to skull base

Type B (Access to petrous apex and clivus)

Indications:

Chordoma, chondroma of clivus
Dermoid/epidermoid cysts
Meningioma, craniopharyngioma, plasmacytoma
Squamous cell carcinoma of petrous apex
Arachnoid cyst

Type C (Access to parasellar region and nasopharynx)

Indications:

Advanced JNA (Stage III/IV)
Salvage surgery for nasopharyngeal SCC
Adenoid cystic carcinoma around the Eustachian tube
Parasellar tumours

Preauricular Approaches (Anterolateral)

Provide access to: jugular bulb, ICA, petrous apex, clivus, pterygomaxillary fossa, and nasopharynx. Particularly useful for paramedian lesions involving the clivus, parasellar area, pterygomaxillary fossa, and nasopharynx.

Endoscopic Endonasal Approaches

Increasingly used as an alternative for paramedian lesions involving the clivus, parasellar area, pterygopalatine fossa, nasopharynx, and occasional ITF involvement - avoiding the morbidity of open lateral approaches.

6. Surgical Hazards in ITF Surgery

Structure at Risk	Consequence of Injury
Facial nerve (CN VII)	Facial paralysis - requires anterior transposition in Type A
Internal carotid artery	Life-threatening haemorrhage
Internal jugular vein	Major haemorrhage, air embolism
Mandibular nerve (V3)	Anaesthesia/paraesthesia of lower face, jaw, tongue
Chorda tympani	Loss of taste (anterior 2/3 tongue), dry mouth
Maxillary artery branches	Haemorrhage; embolisation sometimes required preoperatively
Pterygoid venous plexus	Significant venous bleeding; route of septic spread
CN IX, X, XI, XII	Lower cranial nerve palsies (type A approach)

7. Clinical Points for ENT Practice

Trismus (restricted jaw opening) is a key clinical sign of ITF involvement by tumour or infection, as the pterygoid muscles are encased in this space.
Infection in the ITF (e.g., from third molar periapical abscess, parapharyngeal abscess) can track to the orbit and cavernous sinus via the pterygoid venous plexus - a surgical emergency.
Referred otalgia via the auriculotemporal nerve (branch of V3) is a presenting feature of ITF tumours.
V3 blocks and otic ganglion blocks for pain management are performed within the ITF, guided by imaging or landmark technique.
JNA staging specifically documents ITF extension as this determines surgical approach and resectability.
Preoperative angiography and embolisation of the maxillary artery branches are often performed before ITF tumour surgery to reduce intraoperative blood loss.

Summary Table

Category	Key Points
Boundaries	Roof: greater wing of sphenoid + squamous temporal; Lateral: ramus of mandible; Medial: lateral pterygoid plate + pharynx; Anterior: posterior maxilla
Contents	Pterygoid muscles, V3 + branches, chorda tympani, otic ganglion, maxillary artery + branches, pterygoid venous plexus
Communications	Orbit, middle cranial fossa, pterygopalatine fossa, temporal fossa
Common pathology	JNA, glomus tumours, deep parotid tumours, NPC extension, maxillary Ca, cholesteatoma
Surgical approaches	Fisch Type A (temporal bone), Type B (clivus), Type C (nasopharynx/parasellar)
Key hazards	Facial nerve, ICA, IJV, lower cranial nerves, pterygoid venous plexus

Sources:

Cummings Otolaryngology Head and Neck Surgery, Chapter 175 (Anatomy of the Infratemporal Fossa) and Chapter 178 (Infratemporal Fossa Approaches)
K.J. Lee's Essential Otolaryngology, Chapter on Infratemporal Fossa and Surgery of the ITF
Gray's Anatomy for Students, Head and Neck section

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