TEMPERATURE-CORRELATED HISTOPATHOLOGIC CHANGES FOLLOWING MICROWAVE THERMOABLATION OF OBSTRUCTIVE TISSUE IN PATIENTS WITH BENIGN PROSTATIC HYPERPLASIA

Objectives. To determine the intraprostatic pathologic changes followi ng accurately measured doses of transurethral microwave thermal energy in patients with benign prostatic hyperplasia. Methods. Eight patient s scheduled for prostate surgery were treated for approximately 1 hour without anesthesia using a newly designed microwave treatment cathete r that allows a close impedance match to prostate tissue and concentra tes thermal energy preferentially in the anterior and lateral prostate gland. Interstitial, urethral, and rectal temperatures were continuou sly measured using a novel stereotactic thermal mapping technique. Ser ial sections of prostate tissue harvested during subsequent surgery we re evaluated pathologically with prostate mapping. Results. Microwave treatment resulted in marked and continuous intraprostate temperature elevation, while urethral and rectal temperatures remained low. Peak i ntraprostate temperatures in individual patients reached as high as 80 degrees C. Mean temperature reached a maximum of 54 degrees C at a ra dial distance of approximately 0.5 cm from the urethra and remained 45 degrees C or higher up to a distance of 1.6 cm. The predominant patho logic findings were uniform hemorrhagic necrosis and tissue devitaliza tion without significant inflammation. The mean distance from the uret hra to the viable-necrotic tissue border was 1.6 +/- 0.2 cm (range, 0. 5 to 2.5). At this border, no more than 1 mm in thickness, temperature averaged 45.7 +/- 0.6 degrees C, and there was a suggestion that pure stromal nodules were more resistant to thermal injury. Conclusions. M icrowave treatment can destroy obstructive prostate tissue while maint aining innocuous urethral and rectal temperatures. Temperatures of 45 degrees C or higher for approximately 1 hour cause uniform thermoablat lon of prostate tissue.