MANAGEMENT OF VESTIBULAR SCHWANNOMAS (ACOUSTIC NEUROMAS) - RADIOLOGICAL FEATURES IN 202 CASES - THEIR VALUE FOR DIAGNOSIS AND THEIR PREDICTIVE IMPORTANCE

OBJECTIVE: Tumor-induced bony and soft tissue findings might reflect, in part, the biological characteristics of vestibular schwannomas and could predict clinical findings. In addition, the role of the individu al anatomic conditions of the posterior fossa is of interest to the su rgeon. METHODS: Of 1000 vestibular schwannomas treated surgically at t he neurosurgical department at Nordstadt Hospital, 202 cases, which we re consecutively investigated at the same computed tomography (CT) uni t and using the same technique (high-resolution CT at bone windows bef ore and after surgery, contrast-enhanced high-resolution CT before sur gery, and native high-resolution CT after surgery), were evaluated for special radiological features. Evaluation included, in 103 cases, ana tomic parameters of the petrous bone and posterior fossa cavity and, i n 202 cases, tumor-induced changes of bony structures, tumor relations with bony structures and with neural structures, and postoperative fi ndings of bony structures and of neural tissues. These radiological pa rameters and the related clinical pre- and postoperative findings were transferred to a database for statistical evaluation of their positiv e or negative correlations, i.e., for their reliability in diagnosis a nd their importance in predicting postsurgical outcome. RESULTS: As im portant parameters, the following could be identified. The length of t he posterior auditory canal wall and the interear difference of the ma ximum porus width both correlate with the degree of preoperative heari ng deterioration (P < 0.05). The extent of the widening of the interna l auditory canal is of predictive importance for the chances of postop erative hearing preservation or hearing loss (P < 0.01). The extent of tumor growth anterior and caudal to the internal auditory canal in la rge tumors is of significant importance for prediction of postoperativ e hearing function (P < 0.05). The tumor extension in all directions a nd the extent of cystic tumor components correlate with the pre- and p ostoperative function of the facial and cochlear nerves. The positions of the labyrinthine structures and their geographical relations to th e fundus and the sigmoid sinus and, thereby, to the suboccipital route , enable reliable calculations of the danger of labyrinthine destructi on and help improve the planning of the surgical strategy. DISCUSSION AND CONCLUSIONS: In addition to the importance for surgical planning, preoperative bone window CT and contrast-enhanced images offer the opp ortunity to identify traits of tumor biology, such as bony destruction of the internal auditory canal, tumor shape and cyst formation, and a spects with predictive importance for postoperative outcome. The avera ge size for hearing preservation in tumors was 14.5 x 16.5 x 11.8 mm ( coronal x sagittal x axial). The recent finding (8) of a higher presen tation age in female patients has an apparently anatomic basis, which is a relatively larger internal auditory meatus.