Preservation of hearing in patients undergoing microsurgery for vestibular schwannoma: degree of meatal filling

Object. Preservation of hearing has become a standard goal in selected patients undergoing surgery for a vestibular schwannoma (VS). This study was aimed at analyzing the role played by filling of the internal auditory canal (IAC) as well as those played by preoperative hearing quality, and tumor size in the postoperative preservation of serviceable hearing (SH). Methods. Three hundred eighty-six patients with VS were treated. Hearing preservation was attempted in 128 cases (33.2%) by using intraoperative monitoring and following a retrosigmoid approach. The maximal extrameatal size of the tumor, its extension within the IAC, and pre- and postoperative hearing quality, according to the Gardner-Robertson classification, were evaluated. Preservation of SH was achieved in 24.2% of the 128 patients. With respect to tumor size, SH was preserved in 39% of 77 patients harboring a tumor 15 mm wide or smaller and in 2% of 51 patients with lesions 16 mm wide or larger (p < 0.001). With regard to filling of the IAC, among 63 patients harboring a tumor 15 mm or smaller, in whom magnetic resonance images were available, SH was preserved in 52.8% of 36 patients with partial filling and in 25.9% of 27 patients with complete filling (p = 0.032). Concerning preoperative hearing quality, in the patients with tumors 15 mm or smaller, SH was preserved in 46.5% of 43 patients with Gardner-Robertson Class I hearing and 29.4% of 34 patients with Class II hearing (p = 0.126). Both tumor size and the extent of IAC filling proved statistically significant in a multivariable analysis (p < 0.001 and p = 0.026, respectively). Conclusions. Incomplete filling of the IAC and a tumor size of 15 mm or smaller are independent favorable factors in SH preservation. Excellent preoperative hearing appears to have a positive impact but does not have statistical significance. Intraoperative monitoring is useful in guiding the dissection; however, the surgeon's knowledge of topographical landmarks and meticulous surgical technique remain the essential factors of success.