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CT of the adverse effects of therapeutic radiation of the central nervous system.

Clinical deterioration during or after radiation of the central nervous system may be due to progression of, or a complication induced in, the lesion being treated. Deterioration may also be due to an adverse effect of the radiation on nervous tissue or vessels within the beam, to alteration in the blood-brain barrier, thus influencing the effects of drug therapy, or to a superimposed catastrophe unrelated to the treatment. Transient effects, which occur within the first 3 months of radiotherapy, include increase in symptoms suggesting enlargement of the tumor and the somnolence syndrome that occurs in children. Classical permanent radiation effects include necrosis, atrophy, calcification, necrotizing leukoencephalopathy, mineralizing microangiopathy, aneurysm formation, tumor induction, and cerebrospinal fluid fistulae. Rarely, demyelination occurs with higher doses than are currently used. The permanent effects tend to occur later than the transient ones; some are progressive and many have serious consequences. The appearances of mineralizing microangiopathy are specific; but the nature of the other complications is only evident in the clinical context, although there may be difficulty distinguishing between radiation necrosis and further growth of an intracerebral tumor. Selected cases illustrate the computed tomographic features of these entities.