Acute histological effects of interstitial hyperthermia on normal rat brain

Histological changes in the brains of Fischer rats at different times after interstitial heating with various thermal doses were studied. The brains, subjected to sham-heating, and heating at 39 and 40 degrees C for 30min sho wed mild capillary congestion and minimal vacuolation at 4, 24 and 72h. In the brains heated to 41, 42 and 43 degrees C for 30 min, there was local va scular congestion, petechiae, vacuolation and cellular shrinkage with nucle ar pyknosis at 4h; enhanced congestion and petechiae, acute cellular necros is, infiltration of polymorphonuclear leukocytes and marked vacuolation at the margin at 24 h; total coagulative necrosis of all parenchymal and vascu lar elements, early liquefaction necrosis and vascular hyperplasia at the m argin at 72 h; enhanced vascular hyperplasia at the margin at 120h and 168h . The threshold thermal dose for the histopathological damage in the rat br ain was heating at 41 degrees C for 30 min.