DISTANCE FROM THE LABYRINTHINE PORTION OF THE FACIAL-NERVE TO THE BASAL TURN OF THE COCHLEA - TEMPORAL BONE HISTOPATHOLOGIC STUDY

The middle cranial fossa approach to lesions of the geniculate ganglio n and internal auditory canal preserves cochlear function and affords access to the lateral internal auditory canal. The labyrinthine portio n of the facial nerve Lends to course near the basal turn of the cochl ea, just beneath the middle cranial fossa floor, and is usually dissec ted in this approach. To determine the distance from the labyrinthine portion of the facial nerve to the basal turn of the cochlea, measurem ents were obtained in the temporal bones of 24 subjects (48 ears) 9 to 76 years of age, These subjects had no history of facial nerve or ear disease, and had normal audiograms, The distances ranged from 0.06 to 0.80 mm, with 21 of 24 right ears (87.5%) showing distances less than the standard size of the smallest diamond drills (0.6 mm), and 18 of 24 (75%) less than 0.5 mm. Incidental note is made of the distance fro m the geniculate ganglion to the ampulla of the superior semicircular canal, which ranged from 2.06 to 4.88 mm in the 48 specimens, These me asurements can serve as guidelines for the surgeon working in the midd le cranial fossa.