EXPERIMENTAL RADIO-NECROSIS OF THE BRAIN IN RABBITS

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Abstract
Unanesthetized adult rabbits were exposed to single doses of X-irradiation over a 3x4 cm. field on the left side of the unshaved head. Approx. depth doses were 85% at 1 cm., 70% at 2 cm. and 57% at 3 cm. Group I (13 animals) received 2850 r at the surface; Group II (5), 2440 r; Group HI (2), 2030 r and Group IV (2), 1625 r. The animals of Group I permitted to survive developed irritability, loss of appetite and neurological signs about the 100th day. Macroscopic discoloration of the left cerebellum and deep cerebrum was observed in animals sacrificed post-symptomatically. No microscopic changes were observed in animals killed before the 82d day. The earliest cerebral lesions, found at 82, 85 and 90 days, were ball and ring hemorrhages and anemic necroses around capillaries and arterioles. The latter showed blurred basement membranes and swollen endothelium. Tissue particles nearby stained like fibrin. Microglia were in the perivascular foci. There was no gliosis. Neurones were normal but axis cylinders were sometimes fragmented in necrotic areas. Cerebellar cortical hemorrhages showed patchy loss of Purkinje cells and gliosis. Perforating vessels were tortuous and showed collagenous thickening. Post-symptomatic animals showed old lesions in the same areas as presymptomatic ones with increase in size and new lesions. There was arteriolar necrosis and thrombosis. The cerebral cortex and meninges were unchanged. Group II showed a prolonged asymptomatic stage with more pronounced vascular changes. Hyaline collagenous thickening was present in some foci. Groups III and IV were normal. A similarly treated series of mice showed no changes.

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