Ultrastructural Investigation of Neuronal Damage induced by Interstitial Radiofrequency Hyperthermia in Adult Dogs

A study was conducted using electron microscopy to investigate hyperthermia-induced damage to neurons and myelinated nerve tracts in order to determine the thermal threshold. Twenty adult dogs were used. After parietal craniectomy, four electrode meedles connected to a Thermotron-RF8 for interstitial 8-MHz radiofrequency hyperthermia were inserted in a 1 cm square pattern and placed at a depth of 1.5 cm from the brain surface. One thermocouple microprobe was set in the center of the square formed by the electrodes. One hour after heating for 15, 30, 45 and 60 minutes with set temperatures of 42℃ and 43℃, the animal's a brain was removed and the ultrastructural investigation was performed. The findings suggested that the normal brain adjacent to a tumor in vivo would be damaged irreversibly by a large thermal dose, and that neurons showed ultrastructura changes such as swollen or empty of mitochondria and central chromatolysis even after small and moderate thermal doses.