Infratemporal Fossa: Detailed Anatomy, Communications, Clinical Importance, and the Fisch Approach

1. BOUNDARIES (Walls) of the Infratemporal Fossa

The fossa is continuous superiorly with the temporal fossa (through the space deep to the zygomatic arch).

• Cummings Otolaryngology, p. 3349-3350
• KJ Lee's Essential Otolaryngology, p. 703

2. CONTENTS of the Infratemporal Fossa

Muscular

• Lateral pterygoid muscle - two heads:
  • Superior head: arises from the roof of the infratemporal fossa (infratemporal surface of greater wing of sphenoid)
  • Inferior head: arises from the lateral aspect of the lateral pterygoid plate
  • Both insert onto the TMJ (articular disc + neck of condyle)
• Medial pterygoid muscle: originates from the medial aspect of the lateral pterygoid plate; inserts on the medial surface of the angle of the mandible and ascending ramus
• Temporalis tendon: insertion on the coronoid process

Neural

• Mandibular nerve (V3) - the dominant nerve of the ITF; exits the skull through the foramen ovale and immediately divides into:
  • Anterior division (mainly motor): masseteric nerve, deep temporal nerves, nerve to lateral pterygoid, buccal nerve (sensory to buccal mucosa)
  • Posterior division (mainly sensory): auriculotemporal nerve, lingual nerve, inferior alveolar nerve
  • Motor supply: temporalis, masseter, medial and lateral pterygoids (muscles of mastication)
• Chorda tympani (branch of CN VII): exits petrotympanic fissure, joins the lingual nerve in the ITF; carries taste from anterior 2/3 tongue and preganglionic parasympathetics to submandibular ganglion
• Otic ganglion: lies medial to V3, just below foramen ovale; receives lesser petrosal nerve (preganglionic parasympathetics from CN IX); postganglionic fibres ride on the auriculotemporal nerve to the parotid gland
• Lesser petrosal nerve: carries parasympathetics from CN IX (Jacobson's nerve) to the otic ganglion

Vascular

• Enters the ITF posterior to the ramus of the mandible, passes lateral to the lateral pterygoid muscle
• Divided into 3 parts:
  1. Mandibular part (1st part): branches include the middle meningeal artery (exits via foramen spinosum), inferior alveolar artery, anterior tympanic artery, deep auricular artery
  2. Pterygoid part (2nd part): deep temporal arteries, masseteric artery, pterygoid branches, buccal artery
  3. Pterygopalatine part (3rd part): enters pterygopalatine fossa via pterygomaxillary fissure

• Cavernous sinus (via emissary veins through foramen ovale/spinosum)
• Ophthalmic veins (via inferior orbital fissure)
• Pharyngeal venous plexus

• Cummings Otolaryngology, p. 3349-3351

3. COMMUNICATIONS of the Infratemporal Fossa

Anterior to V3 and the middle meningeal artery, following the floor of the middle cranial fossa and horizontal ICA, the ITF gives access to the cavernous sinus, sphenoid sinus, and nasopharynx.

• Cummings Otolaryngology, p. 3350

4. CLINICAL IMPORTANCE

A. Spread of Infection

• Dental infections (molar teeth) can spread to the parapharyngeal, masticator, and ITF spaces
• The pterygoid venous plexus can carry septic emboli to the cavernous sinus

B. Trismus

C. Tumors

• Nasopharyngeal carcinoma - classic spread into ITF via eustachian tube and lateral wall
• Juvenile nasopharyngeal angiofibroma (JNA) - grows into the ITF via the pterygomaxillary fissure
• Parotid malignancies - extend posteriorly
• Glomus jugulare tumors - extend into posterior ITF
• Salivary gland cancers, squamous cell carcinoma, cholesteatoma of the temporal bone
• Chordoma, chondrosarcoma - from clivus/petrous apex into ITF

D. Perineural Spread

E. Anesthetic Relevance

• Inferior alveolar nerve block (dental anesthesia): targets the mandibular foramen inside the ITF
• V3 block at foramen ovale and infratemporal pterygopalatine fossa blocks are performed for trigeminal neuralgia and pain management

5. THE FISCH INFRATEMPORAL FOSSA APPROACH

Overview of the Three Types

FISCH TYPE A APPROACH

• Glomus jugulare/tympanicum tumors (paragangliomas)
• Salivary gland cancers
• Squamous cell carcinoma of the temporal bone
• Cholesteatoma
• Neurinoma (schwannoma of lower cranial nerves)
• Meningioma, rhabdomyosarcoma, teratoma, myxoma

1. Incision: Large C-shaped postauricular incision extending anterosuperiorly into the temporal scalp and anteroinferiorly into the neck (depending on the required cervical/anterior exposure needed)
2. Flap elevation: Flap raised superficial to temporalis, SCM, and postauricular musculature
3. EAC transection: Cartilaginous external auditory canal (EAC) transected at the bony-cartilaginous junction; a periosteal flap pedicled on the EAC anteriorly is created
4. EAC closure: The lateral EAC is everted and closed primarily (meatal skin everted through meatus). The periosteal flap is rotated anteriorly and sutured to the closed EAC to reinforce the closure medially
5. Middle ear entry: Osseous EAC skin elevated circumferentially to the tympanic annulus; middle ear entered. Incudostapedial joint separated, incus removed, tensor tympani tendon sectioned, EAC skin/TM with malleus removed
6. Radical mastoidectomy: Removal of osseous EAC and all air cell tracts lateral and adjacent to the otic capsule. Stapes suprastructure removed. Eustachian tube obliterated
7. Facial nerve skeletonization: CN VII skeletonized from the geniculate ganglion to the stylomastoid foramen in preparation for transposition
8. Mastoid tip removal: SCM released from mastoid tip; tip itself skeletonized and removed; bone removed over the posterior belly of digastric
9. Cervical dissection: CN IX, X, XI, XII, ICA, and internal jugular vein (IJV) exposed in the neck
10. Facial nerve anterior transposition: The facial nerve is mobilized from stylomastoid foramen, translocated anteriorly (cutting GSPN if needed for type B/extensive type A)
11. ICA dissection: Internal carotid artery dissected from the neck up to the skull base, to its position below the cochlea; bone removed over carotid canal to expose the vertical (petrous) ICA
12. Jugular bulb and sigmoid sinus exposure: Sigmoid sinus ligated below the mastoid emissary vein; jugular bulb exposed
13. Tumor removal: With vascular control achieved, the paraganglioma or tumor is resected (see surgical illustration below)

Fig. - Fisch Type A infratemporal fossa approach: (B) Facial nerve identification, (C) Internal jugular vein and internal carotid artery exposed - Cummings Otolaryngology, Fig. 178.15/178.17

FISCH TYPE B APPROACH

• Chordoma (clivus)
• Chondroma / low-grade chondrosarcoma
• Squamous cell carcinoma
• Dermoid/epidermoid cysts of petrous apex
• Meningioma, craniopharyngioma, plasmacytoma, arachnoid cyst

• Steps identical to Type A up to facial nerve transposition, which is usually not required
• Temporalis muscle is reflected (still attached to coronoid process and zygoma) allowing a retractor to expose the superior ITF
• The middle meningeal artery and mandibular branch of V (V3) are transected - this opens up the superior 4 cm of the ITF
• The ICA can be uncovered from its vertical segment to its anterior limit at the foramen lacerum, after separation from soft tissues around the eustachian tube
• The petrous apex is accessed with careful anterolateral retraction of the ICA
• Can be combined with temporal craniotomy for additional middle fossa and clival exposure

Fig. 178.27 - Fisch Type B: Elevation of the ICA permits access to petrous apex and clivus. Note middle meningeal artery and mandibular branch of V. - Cummings Otolaryngology

FISCH TYPE C APPROACH

• Salvage surgery for squamous cell carcinoma
• Adenoid cystic carcinoma involving the eustachian tube region
• Advanced juvenile nasopharyngeal angiofibroma (JNA)
• Rostral clivus tumors, cavernous sinus lesions, sphenoid sinus tumors
• Parasellar tumors

• The type C approach is an anterior extension of the type B approach
• Access is gained to: rostral clivus, cavernous sinus, sphenoid sinus, peritubal space, pterygopalatine fossa, nasopharynx, and the full anterosuperior ITF
• Pterygoid base removal: The base of the pterygoid process is drilled/removed; this uncovers:
  • V2 (maxillary nerve) at the foramen rotundum
  • The inferior orbital fissure
  • Entry into the sphenoid sinus and cavernous sinus
• Exposure extends anterior to the foramen lacerum up to the posterior wall of the maxillary sinus and nasopharynx

Fig. 178.29 - Fisch Type C: (A) Pterygoid base dissection with V2 exposed, Eustachian tube visible. (B/C) Sphenoid sinus entered, cavernous sinus accessible. - Cummings Otolaryngology

6. COMPARISON SUMMARY TABLE

7. COMPLICATIONS OF FISCH APPROACHES

• Facial nerve palsy - the most significant risk, especially in Type A where anterior transposition is performed. Significant permanent facial weakness can result
• Hearing loss - sacrifice of ossicular chain and middle ear; in type B/transcochlear the otic capsule may be removed (sensorineural loss)
• ICA injury - catastrophic; requires preoperative balloon occlusion testing
• Lower cranial nerve deficits (IX, X, XI, XII) - from cervical dissection and jugular foramen dissection
• CSF leak - from dural entry
• Sigmoid sinus/jugular vein thrombosis
• Eustachian tube dysfunction - managed by obliteration during surgery

8. ENDOSCOPIC ALTERNATIVES

• Cummings Otolaryngology Head and Neck Surgery, 7th Ed., Chapters 175 and 178 (Anatomy of the Infratemporal Fossa; Infratemporal Fossa Approaches), pp. 3349-3351, 3416-3422
• K.J. Lee's Essential Otolaryngology, 11th Ed., Chapter 37 (Infratemporal Fossa; Surgery of the Infratemporal Fossa), pp. 703, 895-896

How to Draw the ITF in an Exam

Step 1 - Draw the bony framework (dotted = cut away)

• Draw the zygomatic arch horizontally at the top (cut away with dotted lines)
• Draw the ramus of mandible on the lateral side (cut away, dotted)
• Mark the infratemporal crest of sphenoid as the roof

Step 2 - Mark the foramina on the roof

• Foramen ovale - V3 comes down through here
• Foramen spinosum - middle meningeal artery goes up here
• Pterygomaxillary fissure - leads to pterygopalatine fossa (medially)

Step 3 - Draw the muscles

• Lateral pterygoid (two heads - upper from sphenoid roof, lower from lateral pterygoid plate) converging on TMJ
• Medial pterygoid deeper and medial, running down to angle of mandible
• Temporalis tendon inserting on the coronoid process

Step 4 - Draw nerves (yellow / pencil label N.)

• V3 trunk from foramen ovale dividing into:
  • Anterior: buccal nerve
  • Posterior: auriculotemporal, lingual, inferior alveolar (going into mandibular foramen)
• Chorda tympani sweeping down from above to join the lingual nerve
• Otic ganglion - small oval just below foramen ovale, medial to V3

Step 5 - Draw arteries (red)

• Maxillary artery entering from behind the mandibular neck
  • 1st part: gives off middle meningeal + inferior alveolar
  • 2nd part: runs through pterygoid muscles (deep temporal, masseteric, buccal branches)
  • 3rd part: exits via pterygomaxillary fissure

Step 6 - Draw the pterygoid venous plexus (blue stippled area)

• Surround the pterygoid muscles with a blue dotted network
• Show it draining into the maxillary vein posteriorly

Step 7 - Label communications (arrows pointing to edges)

• → Orbit (inferior orbital fissure)
• → Middle cranial fossa (foramen ovale + spinosum)
• → Pterygopalatine fossa (pterygomaxillary fissure)
• → Temporal fossa (deep to zygomatic arch)