[Changing radiological results, pitfalls and criteria of failure]

To evaluate the morphological changes occurring during the Years following radiosurgery in order to better define the cure-failure parameters.

Between July 1992 and January 2002 the otoneurosurgical group of the Timone Hospital in Marseille have operated 1000 vestibular schwannomas. The MR imaging performed before (at diagnosis) during and after radiosurgery (6 months, 1 year, 2 years, 3 years, 5 years, 7 years and 10 years) was carefully studied. Systematically six lenghts measurements were obtained for each lesion.

Preoperatively 129 patients were had progressive tumors. At time of radiosurgery, median tumor Volume was 732mm3 (mean: 1346, range: 20-14405). According to the Koos topographical classification, lesions were stage I in 80 patients, stage II in 538 patients, stage III in 322 patients and stage IV in 56 patients. A clear loss of the central enhancement was visible on the postoperative MR control at 6 months and/or 1 Year in 45.5% of patients. In 64% of these patients, this loss of the central contrast enhancement have disappeared. A significant increase of the tumor size was recorded in 15% of the patients. The median increase was 62% (mean: 78%, range: 30-350%). Progression led to salvage surgery (either resection or radiosurgery), in only 3% of the patients.

The specificity of the morphological changes after radiosurgery, when ignored, can lead to misinterpretation and eventually to inappropriate decisions, dangerous for the patient. The analysis of our results had led us to consider continuous progression after 3 Years as mandatory to retain the diagnosis of failure.