An external reference to identify the internal auditory canal in middle fossa surgery

Traditional middle fossa landmarks, such as the facial hiatus and arcuate eminence, are often unreliable. This study was performed to establish an external reference from which to identify precisely the surgical anatomy of the middle fossa. The head of the malleus was identified from the middle fossa in the temporal bones of 20 adults. The lateral cortex of the temporal squamosa at the zygomatic root was used as the external plane of reference. The head of the malleus was consistently located 18 mm medial to the outer cortex on a line perpendicular to the reference plane. Medial extension of this line through the malleus head bisected the internal auditory canal. We recommend this method to precisely locate the malleus head as the first landmark in the middle fossa. Other structures, such as the geniculate ganglion, internal auditory canal, and superior semicircular canal can then be safely identified. We also present our results using this technique in six consecutive patients undergoing middle fossa surgery during the past 12 months.