a matter of weeks. Injury usually involves cell death sufficient to cause impaired function. The latent time for such injuries is equivalent to a particular tissue's cellular turn-over time. For instance, radiation exposures can cause gastrointestinal and hematopoietic syndromes within a week and 2-3 weeks, respectively. Such syndromes result when the tissues can no longer replace their cellular components (2:1-17).
Tissues with a slow turn-over rate and a loss cell loss rate are known as "late-responding (2:1-17)." These may include the brain, spinal cord, lung, liver, and kidney. Radiation's effects in these tissues may become manifest several months to years subsequent to exposure.
Radiation-induced brain injuries can be divided into three general types: (1) the acute response or "acute central nervous system (CNS) syndrome;" (2) the early-delayed response; and (3) late-delayed responses (6:226-229). Much of the damage inflicted upon the nervous system by radiation consists of vascular injury. These pathologic effects include early diffuse edema followed by myointimal proliferation, fibrosis, and necrosis. Other pathologic processes associated with exposure may sometimes additionally include an acute demyelination process (6:226-229).
A whole-body radiation doses exceeding 5,000 rad may cause an immediate central nervous system syndrome. The clinical symptoms of acute radiation brain injury include headache, disorientation, apathy, ataxia, prostration, tremor, increased intracranial pressure, and convul
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