Topographical anatomy of the internal auditory canal. Implications for functional surgery in the cerebello-pontine angle.

For exposure of the cerebello-pontine angle by an enlarged middle-fossa approach without destruction of the inner ear, bone removal anterior and posterior to the internal auditory meatus (c.a.i.) can be performed with orientation at landmarks. Based on the experience of more than 300 interventions and documented by a series of 10 temporal bone micro-dissections, rules have been established for reliable localization of the following structures: geniculate ganglion, Fallopian canal, vertical crest at the fundus of the c.a.i., basal coil of the cochlea, and ampulla of the superior semicircular canal. The surgical technique has enabled the authors to remove acoustic neurinomas of up to 3.5 cm with preservation of hearing in 51%.