Identification of internal acoustic canal in the middle cranial fossa approach: a safe technique

The middle cranial fossa approach (MCFA) is a very valuable functional approach in the armamentarium of the neuro-otologic surgeon. Identification of the internal acoustic canal (IAC) in MCFA is one of the most tedious steps. Many techniques have been described to locate the IAC safely when using the MCFA.

We sought to describe a safe technique for identification of the IAC and to demonstrate its feasibility in temporal bone dissections, as well as to discuss our clinical experience with this technique.

The surgical anatomy of the 20 temporal bones were evaluated and measured, especially by defining the medial and lateral ends of the IAC and relations to the nearby located structures. Measurements were obtained at 3 levels: the width of the IAC at the level of the fundus, the width of the IAC at the level of the porus, and the safe distance around the IAC at the meatal level. The medial and lateral IAC end widths were compared with each other and with the safe area at the meatal level.

The smallest, the largest, and the mean values were recorded. The mean width of the IAC at the level of the porus was found to be more than 3-fold that of the width of the IAC at the level of the Bill's bar, and the ratio between the width of the medial safe area around the IAC and the lateral end of the IAC was found to be more than 7-fold as wide.

This technique offers direct quick exposure of the IAC, without handling the facial nerve and the inner ear structures. Forty-five cases of operations with the same technique showed excellent ease and safety of identifying the IAC medially in the MCFA.