Abstract Otology 2000 C15-4

Tuncay Ulug Prof.Dr.

ENT Department Istanbul University Istanbul Medical Faculty TR-Besiktas, Istanbul

Objective: To demonstrate that the anatomical sturucture, the processus cochleariformis with its intimate and constant relationship to inner ear stuructures, can be used as a reliable landmark in middle cranial fossa surgery alone, or in conjunction with other landmarks. Another objective is to give an indication of the anatomy and relationship of the inner ear and allied stuructures within the intact bone during middle cranial fossa surgery. Study Design: An anatomical prospective study using cadavaric temporal bones to define six reproducible measurements that relate the processus cochleariformis to inner ear structures, which are encountered during middle cranial fossa surgery and 14 other measurements that relate inner ear structures to adjacent structures within the intact bone Method: Using ten cadaver specimens, twenty reproducible measurements were defined. The first six of these measurements define the relation of the processus cochleariformis to inner ear structures in middle cranial fossa surgery. The other measurements give an impression of the inner ear structures and adjacent structures within the intact bone. Using the processus cochleariformis alone, or in combination with other landmarks, the reliability of this landmark in middle cranial fossa surgery was established in four clinical cases. Results: The vertical crest lies at a 20 degree angle from the processus cochleariformis to the coronal plane, and at a distance of 5 to 6 mm from the processus cochleariformis. The point where the medial margin of the basal turn of the cochlea crosses the labyrinthine segment of the facial nerve, is at a 0 degree angle from the processus cochleariformis to the coronal plane, and at a distance of 6.5 to 7.5 mm from the processus cochleariformis. The superior semicircular canal is at a 45 degree angle from the processus cochleariformis to the coronal plane. The medial wall of the vestibulum is 6-7mm from the processus cochleariformis in the same direction. With other measurements important clues about the position of greater superficial petrosal nerve, cochlea, vestibulum and labyrinhine segment of the facial nerve are defined. Conclusions: Middle cranial fossa surgery is a technically demanding procedure, partly due to the lack of easily identifiable landmarks and partly due to limited exposure. If the classical landmarks are indiscernible, then the processus cochleariformis with its intimate and constant relationship to the inner ear structures is a safe and reproducible landmark.