EFFECTS OF INTRAOPERATIVE HYPERTHERMIA ON CANINE SCIATIC-NERVE - HISTOPATHOLOGIC AND MORPHOMETRIC STUDIES

Failure to achieve local control in the treatment of pelvic and retrop eritoneal tumours results in a high rate of recurrences. The objective of intraoperative hyperthermia (IOHT) is to enhance the effect of int raoperative radiation therapy and to increase local tumour control. Th e tolerance of peripheral nerves to heat may limit the heat dose that can be applied to tumours. Histopathologic and histomorphometric chang es of canine sciatic nerve after 60-min IOHT were studied in three gro ups of five dogs each for temperatures of 43, 44 and 45 degrees C. IOH T was performed using a water-circulating hyperthermia device with a m ultichannel thermometry system on surgically exposed sciatic nerve. Hi stopathologic and histomorphometric studies were done immediately, 3 w eeks and 12 months after IOHT. Histologic changes observed immediately after treatment were minimal but at 3 weeks following 60-min 45 degre es C IOHT both axon and myelin loss and an increase in endoneurial fib rous tissue were observed. Twelve months after treatment a statistical ly significant decrease in axon, myelin and small vessel percentages a s well as an increase in endoneurial and epineural connective tissue w ere observed for dog treated to 45 degrees C. Dog treated to 44 degree s C for 60 min had similar statistically significant but less severe c hanges. Twelve months after 43 degrees C IOHT for 60 min, nerve fibres appeared normal and endoneurial connective tissue was only increased mildly around small and medium-sized vessels. These results suggest th at temperatures to the peripheral nerve >44 degrees C for 60 min are l ikely to cause significant histopathologic changes that can be found 1 2 months after treatment. A hypothesis of the mechanism of heat injury to peripheral nerves was developed.