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 individual anatomic conditions of the posterior fossa is of interest to the surgeon.

METHODS: Of 1000 vestibular schwannomas treated surgically at the neurosurgical department at Nordstadt Hospital, 202 cases, which were consecutively investigated at the same computed tomography (CT) unit and using the same technique (high-resolution CT at bone windows before and after surgery, contrast-enhanced high-resolution CT before surgery, and native high-resolution CT after surgery), were evaluated for special radiological features. Evaluation included, in 103 cases, anatomic parameters of the petrous bone and posterior fossa cavity and, in 202 cases, tumor-induced changes of bony structures, tumor relations with bony structures and with neural structures, and postoperative findings of bony structures and of neural tissues. These radiological parameters and the related clinical pre- and postoperative findings were transferred to a database for statistical evaluation of their positive or negative correlations, i.e., for their reliability in diagnosis and their importance in predicting postsurgical outcome.

RESULTS: As important parameters, the following could be identified. The length of the posterior auditory canal wall and the interear difference of the maximum porus width both correlate with the degree of preoperative hearing deterioration (P < 0.05). The extent of the widening of the internal auditory canal is of predictive importance for the chances of postoperative hearing preservation or hearing loss (P < 0.01). The extent of tumor growth anterior and caudal to the internal auditory canal in large tumors is of significant importance for prediction of postoperative hearing function (P < 0.05). The tumor extension in all directions and the extent of cystic tumor components correlate with the pre- and postoperative function of the facial and cochlear nerves. The positions of the labyrinthine structures and their geographical relations to the fundus and the sigmoid sinus and, thereby, to the suboccipital route, enable reliable calculations of the danger of labyrinthine destruction 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 opportunity to identify traits of tumor biology, such as bony destruction of the internal auditory canal, tumor shape and cyst formation, and aspects with predictive importance for postoperative outcome. The average 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 presentation age in female patients has an apparently anatomic basis, which is a relatively larger internal auditory meatus.