Acute effects of interstitial hyperthermia on normal monkey brain--magnetic resonance imaging appearance and effects on blood-brain barrier.

The magnitude and time course of histological and neuroradiological changes due to interstitial hyperthermia in normal cerebral white matter were investigated in eight adult Japanese monkeys. A cooling system enveloping a 2450-MHz microwave antenna was inserted stereotactically into the brain under general anesthesia. A point located 5 mm away from the surface of the cooling system was used as the reference point (RP). Hyperthermia was given to maintain the RP at 43 degrees C for 60 minutes. Two animals were sacrificed under general anesthesia following the intravenous administration of Evans blue, immediately and 1, 3, and 7 days after treatment. After removing the brain, histological changes were investigated. Magnetic resonance (MR) imaging was performed at 1, 3, and 7 days after treatment. Evans blue extravasation was most prominent in the region heated to 43 degrees C or above immediately after treatment. MR imaging showed obvious enhancement in the region heated to 43 degrees C or above 1 day after treatment, related to the disruption of the blood-brain barrier (BBB) by hyperthermia. Three days after treatment, ring-like enhancement with a central low-intensity area was seen in the region heated to about 43 degrees C, caused by BBB disruption and slight neovascularization. One week after treatment, an enhanced ring was observed in the region heated to less then 43 degrees C which surrounded a low-intensity area. The enhancement seen 1 week after treatment was caused by prominent neovascularization. T2-weighted imaging showed a high-intensity area, caused by edema, most prominent 3 days after treatment. Thus chemotherapeutic agents should be given just before the end of hyperthermia.