Three-dimensional computer-aided reconstruction and measurement of the temporal bone for singular neurectomy.

A computer reconstruction method was used to study five normal temporal bones for the three-dimensional anatomy necessary for singular neurectomy. The length of the singular canal was 4.9 +/- 0.6 mm. The distal portion of the singular canal courses at a sharp angle (48.2 degrees) to the direction of the transmeatal surgical approach for this operation. The reconstructions indicated that the singular canal can be exposed by introducing a drill through the external auditory meatus at a point 0.71 mm posteroinferior to the posteromedial margin of the round window on the saucerized medial wall of the round window niche. The distance from this site to the distal end-portion of the singular canal averaged 1.47 mm. The point on the drilling course (from the drilling site to the singular canal) closest to the vestibular end of the hook portion of the cochlea was 0.48-1.00 mm from the drilling site. The reconstructions also indicated that the dissection should proceed superomedially, if necessary, after a 1-mm-deep straight dissection along the transmeatal approach. The ampulla of the posterior semicircular canal, cochlear aqueduct and inferior cochlear vein were all found to lie within 2 mm of the drilling point.