Computer assisted tomography of focal cerebral radiation necrosis in the monkey.

The right occipital lobe in a series of pubescent monkeys was exposed to 3500 rads of orthovoltage radiation in a single dose. Sixteen to 38 weeks later the irradiated region broke down, rather abruptly. The visual evoked response, funduscopic photography, cerebral spinal fluid determinations for protein and lactic dehydrogenase, and computer assisted tomography (CAT) were used to anticipate and reflect the breakdown in neural tissue. CAT scanning demonstrated the two main effects of focal delayed radiation necrosis in this model (in a representative monkey): pronounced vasogenic edema from a break in the blood brain barrier, and contralateral hydrocephalus from brain distortion with obstruction of cerebral spinal fluid circulation. These findings were confirmed by postmortem examinations.