LOCAL IRRADIATION OF CNS WITH HIGH ENERGY PROTONS 353 



Cavities of varying size and shape were inacroscopically seen in about 

 half of the irradiated rabbits. They involved mainly the white matter, but 

 in some cases the cortex was also affected (Fig. 6). Cavitation was first ob- 

 ser\ed 10 weeks after irradiation. In some animals, surviving up to a year, 

 no cavities appeared. The cavities were not encapsulated, but were lined by 

 glial cells and giant cells and contained clear ffuid and macrophages. 



Teleangiectasis of the irradiated region was a striking feature. It 

 was present in all animals surviving more than 23 weeks. The cortex and 

 white matter exhibited numerous blood-filled, thin-walled capillaries of wide 

 caliber lined by a single layer of endothelial cells. Occasionally some of these 

 capillaries were thrombosed, and sometimes small hemorrhages and collec- 

 tions of hemosiderin-filled phagocytes were found around them (Fig. 7). 

 Large hemorrhages were never encountered. 



A thin zone of the cortex immediately underlying the pia matter showed 

 less damage than the rest of the irradiated cortex. 



It was an unexpected finding that the ependyma and choroid plexus al- 



'V, 



V 



V 



Fig. 6. Sixteen weeks after irradiation. The damaged region shows loss of substance 

 and the formation of small cavities in the deeper parts of the cortex and white matter. 

 Ependyma undamaged. The lesion is slightly broader than the beam. H. \an G. X 20. 

 The photographs are published by courtesy of Acta Radiologica. 



