X-IRRADIATIOX AND DELAYED MYELOMALACIA 239 



At the level in the cord where the lesion was seen in its fullest develop- 

 ment (Figs. 1, 2. and 3), the process had de\eloped into acute malacia 

 terminating in severe liquefaction of the white matter. To some extent, the 

 ventrolateral white columns were more damaged than the dorsal columns, 

 for although dorsal and \entral areas were affected in some rats ' e.g. Fig. 1 ) , 

 the dorsal columns were never selectively changed. In paraffin sections, the 

 afTected areas were spongy or reduced to holes and cystic spaces, bridging 

 across which were scattered skeins of glial and reticular fibrils and minute 

 vessels. As Figs. 1-3 show, the process constantly appeared more severe 

 under the leptomeninx, gradually decreasing in intensity inwards. In most 

 rats the gray matter was intact and never showed acute softening as in the 

 white substance. In the spongy and cystic areas, there were no gitter cells. 

 or so few as not to be noticeable, nor was there any astrocytic or fibrillary 

 response — glial or reticulai' > Fig. 4 ) . Parts of fragmented axis cylinders 

 were scattered throughout the malacic focus, sometimes within what was 

 presumed to be ballooned and liquefied myelin sheaths. There was no 

 meningeal reaction, no hemorrhage, and the spinal nerves and ganglia in 

 the same area were undamaged. 



The lesion described corresponded in its regional distribution to the 

 irradiated area of the body. For e.xample. in animals in which the thorax 

 had been irradiated, only the thoracic cord was afliected. In others, where 

 the spine was selectively irradiated from about sixth cer\ical to second 

 thoracic segment, only that area showed the acute damage. Above and below 

 the focus, secondary iWallerian) degeneration was clearly e\ident. depicted 

 in the pariffin sections by numerous "holes" — i.e., liquefied myelin sheaths 

 and axis cylinders. 



As an example of distribution of the lesions in a thorax-irradiated rat. 

 Fig. 5 is a diagram of slices of the spinal cord cut at different le\els. As 

 sections are studied starting at the first cervical and proceeding in series to 

 the sacral level, normal spinal cord and \ertebral marrow is lound until 

 the irradiated area is reached. The lesion then may start on one side, then 

 the other, and continues until it merges into an irreyular funicular focus of 



Fig. 1. Spinal cord, rat. spine irradiated. Latent period 6' _• months, sacrificed after 

 8 days duration of neuroparalysis. Severe myelomalacia of all parts of white matter — 

 dorsal and ventrolateral columns. Fatty marrow. Lesions in muscle (upper left) not 

 too clear at this magnification (See Figs. 7.A and 7B). Hemato.xylin-eosin. .\bout 

 X 16. (.Area marked by arrow shown in Figure 4). 



Fig. 2. -Another case, rat (17/60). thorax irradiated. Latent period 7 months, 

 duration of signs 2 days. Set' Fig. 5 for distribution of lesions. Malacia confined at 

 this level to lateral column of white matter on one side. Fatty marrow. Hematoxylin- 

 eosin. X 16. 



