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Chapter 10
PREAURICULAR
SUBTEMPORAL–INFRATEMPORAL APPROACH
Emel Avci, Amithaba Chanda, Damirez Fossett
INDICATIONS FOR APPROACH
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Extradural petroclival lesions
Midclivus region extradural lesions
Posterior cavernous sinus lesions
Lesions in the region of Meckel’s cave
ANATOMY
EXTRADURAL ANATOMY
The middle cranial fossa (MCF) is a butterfly-shaped structure, with the two petrous ridges forming an angle of
approximately 100 degrees. It is bounded anteriorly by the
free margin of the lesser wing of the sphenoid, posteromedially by the petrous ridge, and laterally by the squamous
portion of the temporal bone.
There are several important surgical landmarks of the
MCF. Dissection of the MCF usually starts at the arcuate
eminence (AE), which is oriented at right angles to the
petrous ridge. The most anterior point of the bony external auditory meatus (EAM) is located at the level of the
most lateral part of the AE. The central part of the AE is
situated above the loop of the superior semicircular canal
(SSC), which lies at a depth of 1 to 3.5 mm from the bony
surface. Just anterior to the lateral end of the AE is the
tegmen tympani (TT), which is the roof of the middle ear
cavity. The TT is in continuity with the intracranial surface
of the squamosal segment of the temporal bone. It is very
thin and often exhibits small zones of dehiscence connecting the cranial and tympanic cavities. The TT is crossed by
the petrotympanic fissure, the intracranial boundary
between the squamous part of the temporal bone and the
petrous pyramid.
Immediately anterior to the TT, adjacent to the zygomatic root, the floor of the MCF separates the intracranial
cavity from the glenoid fossa. Medial to TT, anterior to the
AE, extending toward the petrous apex lies the orifice of
the canal for the greater superficial petrosal nerve (GSPN).
The position of the orifice is variable and depends on the
length of the canal. Slightly anterior but parallel to the
GSPN runs the lesser superficial petrosal nerve (LSPN). It
exits the cranial cavity at the foramen ovale to join the otic
ganglion.
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Lateral to the canal for the GSPN lies the foramen spinosum (FS), through which the middle meningeal artery
(MMA) enters the cranial cavity. Just anteromedial to the
FS lies the foramen ovale (FO), through which passes the
mandibular division of the trigeminal nerve (V3). FO and
FS are the deepest portions of the MCF floor. A venous
plexus here surrounds the V3 . The foramen rotundum (FR)
and superior orbital fissure (SOF) lay further anteriorly and
medially (Fig. 10–1A).
Medial to the FO and canal of GSPN, the MCF floor in
the region of the petrous apex may be variably dehiscent.
There may be no bone covering the carotid canal. Very
close to the anterior aspect of the petrous ridge, there is a
small prominence, the tubercle of Princeteau, which overshadows Meckel’s cave in which sits the gasserian ganglion. A venous plexus surrounds the gasserian ganglion.
The floor of the MCF is the roof of the inner ear
(Fig. 10–1B, C). Under the floor of the MCF are the cochlea,
the semicircular canals, and the internal auditory canal
(IAC). The cochlea lies anterior to the fundus of the IAC,
3.0 to 4.5 mm deep to the floor of the MCF. It is encased in
very dense compact bone. The superior aspect of the basal
turn lies in close proximity posterior or posterosuperior to
the genu of the internal carotid artery (ICA).
The facial nerve has a complex course in the temporal
bone. The parts of the facial nerve in temporal bone are the
IAC segment, the labyrinthine segment, the tympanic segment, and the mastoid segment. The canal of Fallopius or the
facial canal through the base of the skull is quite long; its
course is Z-shaped, threading its way between the labyrinth
and the tympanic cavity. The anatomic course of the facial
nerve is further complicated by the fact that the segments do
not exist in a single plane. The labyrinthine segment begins at
the fundus of the IAC, bending forward by about 50 degrees,
the general direction of the IAC. The direction of the fallopian
canal here is at right angles to the long axis of the petrous
pyramid. It curves forward and inward skirting the superolateral flank of the basal turn of the cochlea and moves in the
direction of the GSPN. It has a slightly ascending course. Posterolaterally, it comes in close relationship to the SCC, where
it is sandwiched between the superior SCC and the cochlea.
Here it is susceptible to being damaged during drilling of the
bone. The facial nerve then makes a sharp bend posterolaterally, creating the first genu. Here lies the geniculate ganglion, from which arises the GSPN.