Pathological investigation of radiation necrosis

The brain and spinal cord of an 18-year-old male, who suffered from cerebellar medulloblastoma with subarachnoid spread, had been irradiated by a large amount of Linac X-ray: 14,450 rads to the lower thoracic segments and 7,400 rads to the lumbar segments. The tumor at the roof of the 4th ventricle had disseminated along the ventricular system but was limited to the subarachnoid space of the cervical spinal cord. No remarkable changes were found in the volume or consistency of the thoracic and lumbar cord. Elasticity of the lower thoracic segment was greatly diminished and the cut surfaces were yellowish white and fragile. Microscopically extensive coagulation necrosis was observed with complete disintegration of myelin and axon. Vascular changes were most prominent in the smaller vessels, eg. hyalinous thickening, concentric cleavage, adventitial fibrosis and edema of small artery perivascular spaces, fibrin thrombi occulusion of arterioles and capillaries, and telangiectasia. In the lumbar spinal cord, moderate neuronal degeneration and protoplasmic astrocytosis were observed. Changes in the lumbar posterior white column were considered to be not only secondary degeneration but also a primary lesion caused by irradiation. Liquefactive necrosis in the gray matter of the cervical cord was thought to be a nonspecific circulatory disturbance because of the absence of vascular changes. Vascular changes were thought to be very important in the histological diagnosis of radiation myelopathy and it was supposed that increased permeability of the vessel walls was a factor in coagulation necrosis. They considered this case to have typical histology of radiation myelopathy. (Evans, J.)