Surgical anatomy of basal turn in relation to middle cranial fossa and round window as pertaining to middle fossa cochlear implant technique

Purpose The purpose of this investigation was to evaluate the relation of the basal turn of cochlea with middle cranial fossa and round window as pertaining to middle cranial fossa cochlear implant technique. Methods Fifty-four formalin preserved temporal bones were micro-dissected to expose the basal turn. The point (f) was marked on the basal turn of cochlea where there was minimum distance of basal turn of cochlea from the floor of middle cranial fossa (f(1)). The f-f(1) distance, the angle (angle smf) and distance of point "f" from the round window (s-f) was measured. Results The mean minimum distance between basal turn of cochlea and floor of middle cranial fossa (f-f(1)) was 2.0 +/- 0.7 mm.The point f was at mean distance (s-f) and angle (angle smf) of 14.7 +/- 1.6 mm and 217 degrees +/- 13.7 degrees from round window, respectively. Conclusions The information may be helpful for designing appropriate electrode array for middle fossa technique especially for deciding the length of electrode array towards round window, as otherwise electrode may extend into vestibule of inner ear. In the cases where bone thickness between superior part of basal turn of cochlea and middle cranial fossa is < 1.5 mm, surgeon should be extra cautious.