Two- and three dimensional measures of vestibular schwannomas and posterior fossa--implications for the treatment.

BACKGROUND: There is no uniformly accepted method of reporting the size of vestibular schwannomas (VS) and to evaluate the individual tumour behaviour in the posterior fossa (PF). To help the treatment decision we investigated the VS and PF morphometry using a computerized method.

METHOD: Stereotactic fused CISS MR and CT scan images were obtained from 58 adult patients (31 males and 27 females) harbouring an unilateral VS (25 Koos II, 21 Koos III and 12 Koos IV). Using a Gammaplanworking station we screened for the following measures: anteroposterior (AP), craniocaudal (CC), transverse (T) and maximum (Max) diameters (Diam) of the intracisternal part of the tumour, VS and PF volumes.

FINDINGS: The Max Diam was the most accurate way to estimate the tumour volume (Spearman's rho >0.80). Among several parameters, the T Diam was the best measure to assess the brain shift (ROC analysis) with a cut off value at 14.5 mm (91.7% sensitivity and 93% specificity). VS volume and the ratio VS volume/PF volume were also efficient to predict a brain shift.

CONCLUSIONS: Max Diam and T Diam are bedside measured simple data of particular interest to respectively estimate the VS volume and predict the brain shift due to the tumour. The determination of cut-off values correlated to brain shift will provide guidelines at the time of the therapeutic decision between radiosurgical and microsurgical strategy.