Acoustic neuroma: anatomo-clinical correlations in the posterior wall of the temporal bone.

A morphometric study of relationships among cranial nerves V-VI-VII-VIII-IX-X-XI-XII and the posterior wall of the temporal bone was done in 58 specimens. Large variations occurred in measurements. Results were correlated to a clinical study of 30 patients undergoing surgery for removal of acoustic neuromas. No correlations could be found between size and shape of external auditory meatus (E.A.M.) and internal auditory meatus (I.A.M.) in the same temporal bone. Mean distances from the point where cranial nerves enter the temporal bone to the I.A.M. were: trigeminium nerve, 7.8 mm; abducent n., 15.2 mm; hypoglossus n., 21.4 mm; and glossopharyngeal n., 5.3 mm. Although the jugular foramina is the closest structure to the I.A.M., cranial nerves IX-X-XI were never clinically impaired in all 30 patients studied here. Clinically diagnosed trigeminium nerve impairment occurred more often than facial paralysis (33.3% against 20% of patients). It seems that motor fibers are more resistant to tumoral compression and distension.