352 ANDERSSON, LARSSON, LEKSELL, MAIR, REXED AND SOURANDER 



Two weeks after irradiation, collections of fluid and small perivascular 

 hemorrhages were observed in the irradiated zone. Within the lesion many 

 thick-walled capillaries lined by large endothelial cells were present. The 

 nerve cells, axons, and myelin sheaths in the path of the beam were mostly 

 destroyed. In the damaged tissue, proliferation of astrocytes had occurred, 

 and collections of macrophages were seen, particularly around the vessels. 

 Four weeks after irradiation, cells with large nuclei, 2 or 3 times the nor- 

 mal size, were seen among the proliferating astrocytes. Numerous large atypi- 

 cal glial cells appeared within 3 months after irradiation (Fig. 5). Some of 





Fig. 5. Atypical glial cells appeared in the lesion at 4 weeks after irradiation and 

 were more frequent at 10 weeks. Thionin. X 640. The photographs are published by 

 courtesy of Acta Radiologica. 



these were binucleated or multinucleated; many had a huge nucleus of 

 bizarre shape. Inclusion bodies were frequently seen in the nuclei of these 

 cells. Some of the giant cells resembled nerve cells in that they had a large 

 nucleus with a distinct nuclear membrane and a central nucleolus; the nu- 

 cleus was often eccentric, and there was a large amount of glassy cytoplasm. 

 The various types of atypical cells were most frecjuent at the margins of the 

 lesion. They were never seen in other parts of the brain. 



