Microanatomical Study of the Extradural Middle Fossa Approach for Preventing Cochlear Damage

ABSTRACT

OBJECTIVE: The objective is to describe the relationship of anatomical landmark required for the middle fossa approach to preservation of hearing. METHODS: Dissection of 16 fixed human cadaveric heads was performed. we identified a rhomboid-shaped middle fossa landmarks that serve as a guide to minimize cochlea injury. The points of this construct are as follows ; 1) the junction of the greater superficial petrosal nerve and the trigeminal nerve ; 2) the lateral edge of the porus trigemius ; 3) the intersection of the petrous ridge and arcuate eminence ; and 4) the intersection of the lines extended along the axes of the greater superficial petrosal nerve and arcuate eminence. Mean, minimum, and maximum measurements of all distances were determined. RESULTS: The average cochlea-geniculate ganglion distance measured in the dissected specimens was 3.0+/-0.8mm with a range of 1.2 to 4.1mm. The average cochlea-petrous carotid genu distance was 2.9+/-0.9mm with a range of 1.2 to 4.0mm. The average cochlea-internal acoustic meatus distance measured in the dissected specimens was 9.0+/-0.5mm with a range of 7.8-10.9mm. The average cochlea-mandibular nerve distance measured was 9.4+/-0.4mm with a range of 7.6-11.3mm. CONCLUSION: The middle fossa approach requires special knowledge of the anantomy to reduce the risk of damage to cochlea. It is important that the surgeon understand the surgical anantomy. The present study describes the simple geometric construct that proposes to assist in locating the cochlea.