Histopathology of prostatic tissue after transurethral hyperthermia.

Histopathological changes were studied in four patients who had moderate to severe urinary outflow obstruction due to benign prostatic hyperplasia (BPH) and were treated with transurethral microwave hyperthermia (TUMH). All these patients received TUMH with a helical antenna using a BSD 300 unit. The temperature was controlled on the urethral surface at 45 degrees C +/- 1 degree C. Each treatment session lasted 70 min at this temperature. Histological changes were periurethral, extending up to 6 mm radially and 4-5 cm longitudinally. They were symmetrical and most severe in the immediate periurethral zone. The severity and distribution of these histological changes correlated well with the thermal profile of the helical antenna. Acute changes, observed 24-48 h following administration of a single TUMH session, consisted of periurethral oedema, parenchymal haemorrhages and occasional, partial small-vessel thrombosis. Selective coagulation necrosis of the parenchymal smooth muscles with sparing of smooth muscle fibres in the vessel walls was noted. Histopathological changes found in patients 7 or 26 days following the administration of 10 TUMH treatments given twice-weekly for 5 weeks showed more severe and deeper lesions. They consisted of interstitial haemorrhages, complete obliteration of blood vessel lumina due to thrombosis and further evidence of coagulation and haemorrhagic necrosis. Evidence of a reparative process with ingrowth of granulation tissue in various stages of organization was clearly demonstrated. The effect of TUMH on BPH-obstructed urethra is probably expressed through selective shrinking and retraction of the periurethral prostatic parenchyma due to organizing localized tissue necrosis and cicatrization. Details of this complex process will be presented.