Abstract
Objective The absence of precise landmarks in the middle fossa floor and frequent anatomical
variations make it difficult to localize the internal acoustic canal (IAC) during
the middle fossa approach (MFA). We aimed to investigate the reliability and utility
of the neuronavigation system (NNS) in the MFA and to delineate specific technical
considerations regarding NNS during the approach.
Method One-millimeter-thin section computed tomography scans were performed on five formalin-fixed
human cadavers (10 sides). During the MFA, structures, such as the IAC, vestibule
and cochlea hidden in the temporal bone were investigated under NNS guidance.
Results All the superficial landmarks, such as the foramen spinosum and ovale were correctly
localized by NNS. Deeper landmarks, such as the central part of the IAC lying beneath
the surface of the petrous apex could not be localized via NNS. The exact area of
bone removal along roof of IAC was determined by using the orientation provided by
the probe placed between the basal turn of cochlea and the vestibule. We were able
to validate the location of the IAC via a medial to lateral drilling by using the
navigation this reference point.
Conclusion The NNS can be used effectively during the MFA, and localizing superficial landmarks
on the middle fossa floor with a higher accuracy may prove helpful in identifying
the IAC from above. By referring to the cochlea–vestibule junctional area, the exact
location of the trace of the IAC can be revealed.
Keywords
middle fossa approach - internal acoustic canal - neuronavigation - petrous
