Endoscopy of the internal auditory canal during hearing conservation acoustic tumor surgery.

Hearing conservation acoustic neuroma surgery is technically demanding. This is attributable primarily to the formidable anatomic obstacles. The axis of the internal auditory canal (IAC) is oriented at an obtuse angle relative to the posterior petrous ridge. In addition, the labyrinth blocks the view of the lateral 2 to 3 mm of the IAC. These two factors prohibit an unobstructed view of the fundus of the IAC with a standard operating binocular microscope. However, angled rigid endoscopes (30 and 70 degrees) offer excellent views of the lateral portion of IAC. The facial nerve, cochleovestibular nerve, transverse crest, and vertical crest (Bill's bar) can be seen endoscopically. Neuroendoscopic examination is helpful to ensure complete tumor removal in the lateral IAC during acoustic tumor surgery. It is also helpful in visually verifying the continuity of the facial and cochlear nerves at the end of the operation.