Normal brain response after interstitial microwave hyperthermia med./bio.

To assess the extent and time course of radiographic changes induced in dog brain after a single 30 min hyperthermia application (at temperatures of 40, 41, 42, 43 and 44°C). A helical coil microwave antenna was used to induce a small focal lesion in the frontal white matter, and the volumes of necrosis and contrast enhancement were measured weekly for 6 weeks using computed tomography.

• animal
• dog/beagle
• partial body: brain

Heat lesions were characterized by rapid development and resolution and consisted of an area of focal low density surrounded by a ring of contrast enhancement. Histologically, the focus of low density corresponded to regions of tissue necrosis, whereas the ring enhancement showed local reactive changes (including endothelial cell proliferation and infiltration with macrophages).
Tissue necrosis was found at temperatures greater than 43.9 +/- 1.5°C, and volumes of necrosis and ring enhancement were at a maximum 1 week following application. Relative to the contralateral, unheated hemisphere, regional cerebral blood flow in the heated brain appeared to be reduced for the first 3 weeks after application but approached normal by week 4. The mean transit time of blood was increased for weeks 1-3 compared to the untreated hemisphere, and tissue vascularity reached a maximum, 3 weeks after application.
The rapid computed tomography changes together with ultrafast computed tomography and histopathological findings suggest that focal heat lesions in the brain stimulate a significant and rapid vascular response.