Assessment of the Subarcuate Canaliculus as a Landmark in Middle Fossa Surgery.

Background and objectives: The middle fossa approach is commonly used for lesions of the internal auditory canal (IAC). Localization of the superior semicircular canal (SSCC) is key for adequate drilling of the postmeatal triangle and exposure of the posterior IAC. The only available anatomic landmark for the SSCC is the arcuate eminence, which has a variable relationship with the SSCC. This study assessed the potential use of the subarcuate canaliculus (SAC) as a landmark to localize the SSCC and help ensure the safe drilling the postmeatal triangle.

Methods: Sixteen cadaveric specimens of temporal bone were studied (7 fresh human temporal bones and 9 sides of 5 cadaveric heads). An extradural approach to the middle fossa was performed. The postmeatal triangle was drilled, and the SAC, IAC, and SSCC were exposed. Three points were identified along the SAC: the medial end, the lateral end, and a turning point where the SAC has a conspicuous change along its course.

Results: Identified in all specimens, the SAC started on the medial petrous face posterior to the IAC and coursed posteriorly and laterally toward the SSCC. The mean length of the SAC was 10.9 mm. The SAC made a mean superior turn of 42° at its turning point toward its lateral point. Avoiding drilling of the postmeatal triangle lateral to the turning point protected the SSCC while maximizing the exposure of the dura of the posterior IAC.

Conclusion: The SAC may be used as a reliable ancillary landmark in addition to the arcuate eminence to safely localize the SSCC during the drilling of the postmeatal triangle and exposure of the IAC.