[Gamma knife radiosurgery for metastatic brain tumors: neuropathological report of two autopsy cases and review of literatures].

More than 40,000 cases have been treated with gamma knife radiosurgery, but few neuropathological reports are available. This paper describes two autopsy cases in which the patients had been treated with gamma knife. As these patients died 67 and 24 days after therapy, early neuropathological changes are reported. The first case was a 58-year-old woman diagnosed with multiple brain metastases from breast cancer. One of these lesions, in the medullaoblongata, was irradiated with a gamma knife. Sixty-seven days later, she died from heart failure. The second case was a 69-year-old man diagnosed with multiple brain metastases from lung cancer. One of these lesions, in the pons, was irradiated with a gamma knife. Twenty-four days later, he died from acute renal failure caused by hepatorenal syndrome. In both cases, the irradiated lesions were well demarcated from the undamaged surrounding tissues on light microscopy. Histologically, the tumor cells showed a variety of degenerative changes, such as pyknosis, multinuclear cells, and vacuolar degeneration in the cytoplasm. Fibrosis, more prominent in the first case, was observed spreading in the irradiation field, adhering to the hyalinized and thickened vessel walls. Demyelination was also observed in the first case. As far as we know, this report is the first published description of fibrosis in the radiosurgical irradiation field.