6 Exposure via lateral temporal craniotomy provides supralabyrinthine access to the tegmen mastoideum and tympani, fallopian canal, petrous apex, and the internal auditory canal (IAC). The surgeon should be familiar with temporal bone anatomy from a superior perspective unique to the middle fossa approach. The approach to the temporal bone from this perspective requires familiarity with landmarks that aid orientation to the IAC, the intratemporal facial nerve, and the labyrinth within the underlying temporal bone. The external auditory canal provides an initial guide to the location of the internal auditory canal. Although not co-linear, the IAC lies roughly within the same coronal plane as the external auditory canal (EAC). The IAC lies ~1 cm superiorly relative to the EAC (Fig. 5.1). More laterally, the tympanosquamous suture line courses posterolateral to anteromedial toward the tegmen tympani, pointing to the area of several critical landmarks in close proximity: the arcuate eminence (see Chapter 2’s Fig. 2.5), foramen spinosum (carrying the middle meningeal artery), tympanic canaliculus (carrying the lesser petrosal nerve), and the facial hiatus (carrying the greater petrosal nerve). The tegmen tympani may be removed to expose the underlying ossicular heads that lie lateral to the tympanic segment of the facial nerve. Decortication of the internal auditory canal via the middle fossa route is facilitated by serial identification of these landmarks. The arcuate eminence (see Chapter 2’s Fig. 2.5) is visualized as a bony prominence along the surface of the middle fossa floor and approximates the underlying superior semicircular canal which is oriented perpendicular to the petrous ridge. Bone of the eminence is removed to expose the subjacent superior semicircular canal, thus providing the key landmark to the lateral internal auditory canal as discussed below. Note that this bony landmark for the superior SCC is absent or greatly reduced in size in 15% of cases. For the middle fossa dissection, the surgeon sits at the head of the operating table, looking at the patient’s feet. The head is turned just short of 90 degrees to expose the ear of interest. In the laboratory, orient the temporal bone such that the mastoid tip points away from you. The middle fossa craniotomy should be sufficiently an terior to allow exposure of the middle ear space and more medially located internal auditory canal.
Middle Cranial Fossa Approach
to the Internal Auditory Canal
Surgical Anatomy
Dissection
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