Transurethral Prostate Ablation Using Saline-Liquid Electrode Introduced via Flexible Cystoscope

Abstract

An interstitial saline-electrode has been developed to couple radiofrequency (RF) energy to prostate tissue in order to produce large lesions quickly and controllably. In this study, we attempted to produce similar results using a flexible catheter introduced transurethrally via a flexible cystoscope. An insulated 4F catheter with an extendable needle electrode (26-gauge, 5-mm exposed metal tip) was introduced through a port of a flexible cystoscope into the urethra of 10 dogs via a small perineal incision (required for the canine U-shaped urethra). Under visual endoscopic guidance, the electrode was placed in the center of the prostate and the needle electrode extended at an angle into the prostate, one lobe at a time. Hypertonic saline (14.6% NaCl) was infused at 2 mL/min through the needle electrode into the tissue for 30 seconds before and during RF application. The energy (50 W, 475 kHz) was delivered for 30, 45, 60, or 90 seconds (RFT System; U.S. Surgical Corporation). Prostate and urethral temperatures were monitored using thermocouples mounted on the catheter. There was an automatic high-temperature shut-off if the urethra reached >42°C or if impedance reached >300 Ω during RF energy application. Prostate sizes ranged from 1.4 × 2.0 × 1.4 cm to 5.0 × 4.5 × 4.2 cm. In this group, there were no automatic shut-offs at any of the energy durations, and the lesions produced ranged from 1.3 × 1.3 × 1.1 cm (0.99 cm³) to 1.6 × 2.7 × 2.2 cm (5.03 cm³). The average ablation volumes produced were 1.76 cm³ at 30 seconds' RF application, 2.42 cm³ at 45 seconds, 3.96 cm³ at 60 seconds, and 5.03 cm3 at 90 seconds. Histologic examination revealed typical coagulation necrosis in the treatment zone without tissue desiccation. Introduction of the saline-electrode through a flexible cystoscope provides a minimally invasive procedure that quickly and controllably produces large lesions that may provide effective treatment for benign prostatic hyperplasia with less patient discomfort.