Is the entire fundus of the internal auditory canal visible during the middle fossa approach for acoustic neuroma?

Hypothesis: To determine the degree to which the fundus of the internal aud itory canal (IAC) can be visualized during the middle fossa approach (MFA). Background: Conventional wisdom states that the MFA provides excellent acce ss to the LAC from the porus acusticus to the fundus. On the basis of obser vations derived from a substantial surgical experience, it became obvious t hat a variable fraction of the fundus lies obscure from the surgeon's line of sight during the MFA because of(1) the overhand of the transverse crest and/or (2) the immobility of the facial nerve at its entry into the Fallopi an canal. Methods: Intraoperative measurements were performed in ten cases to determi ne the typical angle of view to the fundus of the IAC in the MFA. This angl e of view was projected onto coronal computed tomography scans of 30 tempor al bones. Measurements of the IAC were made to determine the amount of fund us that could not be directly visualized during a MF exposure. Results: On the basis of a surgical line of sight, the fraction of the infe rior compartment of the canal that could not be directly visualized because of overhand of the transverse crest ranged from 14% to 34% (median 25%). Conclusions: Complete resection of IAC tumors involving the fundus via the MFA requires some degree of blind dissection. Specialized tools and techniq ues are required to minimize the risk of neural injury during this indirect dissection. Inspection of the fundus with either mirror or endoscope is of ten necessary to exclude the possibility of retained tumor fragments.