Fig. 4.

Internal auditory canal (IAC) drilling. ( A ) Intradural exposure of the IAC is initiated by removing a semilunar region of the medial petrous temporal bone (purple hash) overlying the porus acusticus ( B ), to a lateral depth based on IAC length, tumor extent and location of posterior semicircular canal. ( C ) With these boundaries established, saucerization of the region overlying the porus carefully proceeds until the IAC dura is identified overlying cranial nerve VIII. ( D ) Taking care to protect the IAC dura and contents, two troughs are extended at the superior and inferior limits of the region of bony removal and carried longitudinally from the porus to the fundus, and ( E ) deepened until at least 180 degrees of circumferential IAC exposure is completed. CN, cranial nerve; PCA, posterior cerebral artery; SCA, superior cerebellar artery; Sup., superior; V, vein.