Radiation-induced morphologic changes in the rhesus monkey (Macaca mulatta) brain

The right cerebral hemisphere of 24 rhesus monkeys scheduled for necropsy a t the completion of another project were studied histopathologically 1-30 d ays after a single dose of Co-60-irradiation. Histopathologically, inflamma tion and gliosis consistently occurred at specific time points but varied i n severity between individuals. Multifocal hemorrhage, edema, and an acute neutrophilic inflammatory response were observed initially whereas perivasc ular accumulations of lymphocytes were observed in specimens at the end of the study. Microglia/macrophages were most prominent during the first week after irradiation, whereas astrocytes were reactive throughout the observat ion period. The early clinical manifestations of the central nervous system (CNS), because of brain irradiation in humans, correspond temporally with acute vascular responses, acute and subacute inflammatory cell responses, a nd subacute demyelination and reactive astrocytic and microglial responses observed in the rhesus monkey. Initial responses of the CNS to gamma-irradi ation may have potential implications for the development of radiation-indu ced late injury of the CNS.