Surgical Classification and Predictive Factors in Acoustic Neuromas

Abstract

This study was undertaken to classify the surgical findings that lead to minimal morbidity in acoustic neuroma surgery. It is well known that hearing preservation and facial nerve function are related to tumor size. We used the Zini-Magnan classification, which is a modification of that of Tos and Thomsen and takes into account not only tumor size but also the relationship with adjacent structures. Surgical findings were recorded concerning tumor extension and relationship between cochlear nerve, facial nerve, and the acoustic neuroma, so as to define predictive factors in hearing and facial nerve preservation. From October 1993 to December 2000,306 patients with acoustic neuroma were operated on. According to our classification, the grading was considered stage I in 37 cases (12%), stage II in 106 cases (35%), stage III in 85 cases (28%), stage IV in 75 cases (24%), and stage V in 3 cases (1%). An additional subdivision for each stage, except intracanalicular stage I, defines the aspects of the internal auditory canal: empty, a: 39 cases (13%); bottom free,b: 82 cases (27%); full filled, c: 185 cases (60%). Regardless of the level of hearing, we used the retrosigmoid approach (215 cases) for small or medium-sized tumors (stages I-III), and the translabyrinthine approach (91 cases) when the tumor was more than 2.5 cm in the cerebellopontine angle (13 cases stage III and all cases in stages IV and V). During 6 months followup for the 306 patients, postoperative House-Brackmann facial nerve grades were the following: grade I, 195 cases (64%); grade II, 70 cases; grade III, 18 cases; grade IV, 16 cases; grade V,2 cases; and grade VI, 5 cases. Of 181 patients, hearing preservation was achieved in 83 cases (46%), type A in 25 cases (13.8%) and type B in 24 cases (13%). Favorable surgical factors for saving facial nerve function were facial nerve anteroinferior to the tumor and close to the cochlear nerve. Favorable surgical factors for preserving hearing were related only to easy cleavage from the tumor.