Classification of Vestibular Schwannoma (Acoustic Neuroma)

Abstract

To improve the understanding of acoustic neuromas and to compare the results of their management, the same reporting system must be used in each subject. Tumor size and location are very important for preoperative assessment of tumor characteristics. Tumors should be classified into four categories: intrameatal (IM), small (S), medium (M), and large (L). The IM tumor is limited to the internal auditory meatus. The S tumor is up to 15 mm in extrameatal size, the M tumor is more than 15 mm and no more than 30 mm, and the L tumor is more than 30 mm. The actual tumor size should be noted as [maximum diameter] × [minimum diameter]. When hearing preservation is attempted, the status of the fundus may be critical. If the fundus is occupied by the tumor, the tumor must be removed by blind dissection, and the cochlear nerve at its most vulnerable part as well as the vessels will be damaged, which results in the failure of hearing preservation. Therefore the status of the fundus should be stated together with the tumor size: e.g., IM, fundus occupied, or M 28 × 24, fundus empty.