Stereotactic radiosurgery of small intracranial tumors: neuropathological correlation in three patients

The mechanism by which radiosurgery can stop the growth of some tumors is poorly understood, in part because postmortem neuropathological findings in patients have been reported only rarely. To define further the effects of radiosurgery, we present the correlation among clinical, neuroimaging, and neuropathological data in three patients with different intracranial tumors who died between 2 and 39 weeks after radiosurgery. The target volumes in two patients with malignant tumors showed sharply demarcated coagulative necrosis. In the third patient, who had a benign acoustic nerve tumor, neuropathological examination found intratumoral hemorrhage and cyst formation, but no necrosis. Radiosurgery appears to cause acute necrosis of malignant cells, although its effectiveness may be limited by the infiltrative nature of some tumors. In benign tumors, necrosis following radiosurgery is relatively delayed, and may not be required for growth arrest.