[Computerized evaluation of tumor volume with MRI. Applications to the surveillance of acoustic neurinoma].

Routine volume measurement techniques most often produce a rough approximate with poor accuracy for smaller structures. The results are generally improved by increasing the examination time, so that the technique then becomes unusable in daily practice. We propose a semiautomated volume calculation method with MRI, and its application to the surveillance of non-operated acoustic neuromas. This calculation technique, based on a threshold-setting method, allows accurately delineating the contours of the structures to be measured on each section and quickly calculating the total volume. After testing its reliability on control volumes, this techniques has been used to assess the evolutive nature of 16 acoustic neuromas with mild symptoms in 15 patients rejected for surgery. The radiological examinations were 428 days apart in average. On the basis of the obtained results, a theoretic tumor doubling time was calculated, thus allowing comparison between all patients. All controlled neuromas had a theoretic doubling time ranging from 427 to 4,884 days, corresponding to little- or non-evolutive lesions, which may be explained by the series selection bias excluding evolutive tumors referred to surgery. Owing to its rapidity and easy use, this semiautomated volume calculation technique for MRI seems to be very interesting as it allows reliably quantifying a volume variation that is usually estimated approximately.