Temperature-correlated histo pathologic changes following microwave thermoablation of obstructive tissue in patients with benign prostatic hyperplasia

Abstract Objectives To determine the intraprostatic pathologic changes following accurately measured doses of transurethral microwave thermal energy in patients with benign prostatic hyperplasia. Methods Eight patients scheduled for prostate surgery were treated for approximately 1 hour without anesthesia using a newly designed microwave treatment catheter that allows a close impedance match to prostate tissue and concentrates thermal energy preferentially in the anterior and lateral prostate gland. Interstitial, urethral, and rectal temperatures were continuously measured using a novel stereotactic thermal mapping technique. Serial sections of prostate tissue harvested during subsequent surgery were evaluated pathologically with prostate mapping. Results Microwave treatment resulted in marked and continuous intraprostate temperature elevation, while urethral and rectal temperatures remained low. Peak intraprostate temperatures in individual patients reached as high as 80 °C. Mean temperature reached a maximum of 54 ° C at a radial distance of approximately 0.5 cm from the urethra and remained 45 °C or higher up to a distance of 1.6 cm. The predominant pathologic findings were uniform hemorrhagic necrosis and tissue devitalization without significant inflammation. The mean distance from the urethra 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 °C, and there was a suggestion that pure stromal nodules were more resistant to thermal injury. Conclusions Microwave treatment can destroy obstructive prostate tissue while maintaining innocuous urethral and rectal temperatures. Temperatures of 45 °C or higher for approximately 1 hour cause uniform thermoablation of prostate tissue.