HISTOPATHOLOGY OF CNS RADIATIOxX 



173 



Fig. 3. Vascular lesion in small leptomeningeal vessel near. an area of myelomalacia. 

 End result of radiation change with fibrosis of wall and complete obliteration of the 

 lumen. Hematoxylin-eosin X250. Dosage 4,440 r Ta'''"' in 29 hours. No neurologic 

 deficit. Sacrifice 4 months after radiation. Autopsy: partial myelomalacia at 12th 

 thoracic and 1st lumbar segments. 



One of the most perple.xins; problems in the histopatholo<;y of radiation 

 reactions is the relation of such lesions to other chano;es induced by this 

 agent. As long ago as 1921, Bagg stated that x-ray injury to the brain is 

 secondary to vascular change. Since that time, workers have been di\ided 

 as to whether the changes in the parenchyma are ischemic and infarctive or 

 whether they are direct eflfects of ionizing radiation without mediation 

 through vascidar mechanisms. The opinion of the author, based on personal 

 material, is in agreement with Arnold's et al. ( 1954b) that the effects on the 

 nervous system are direct effects. The occlusion of vessels could account for 

 areas of complete infarction in the region of their distribution. Such effects, 

 however, are only a minor part of the response of the central ner\ous system 

 to ionizins radiation. 



Effects of Radiation on the Neuron 



Largely through the work of Hicks (1953, 1954), it has become generally 

 recognized that the developing neuron is highly susceptible to ionizing radia- 



