Objectives: Cryotherapy of the prostate has been reintroduced clinically due to improved ultrasound guidance and cryotechnology. The purpose of this canine feasibility study was to assess the accuracy of transrectal ultrasound (TRUE) in monitoring iceball progression with histologic correlation. Methods: Six mongrel dogs received cryotherapy to the entire prostate and were observedfor selected periods of 1 day to 12 weeks with TRUS follow-up. Some technical limitations of the canine model prohibited complete comparison with techniques currently used in humans. Results: TRUS monitoring of posterior iceball progression proved to be highly accurate and correlated with subtotal necrosis of the rectal wall, sparing the mucosal layer with millimeter accuracy. The prostate was completely necrotic in three of six dogs. Scattered residual glands remained at the distal apex in one dog and in the posterolateral periphery of a larger-volume prostate. Cryotherapy missed the prostate in one dog due to pelvic hematoma formation and poor TRUS visualization. Without adequate urethral warming, central sloughing was noted in chronic animals. Histologic examination demonstrated hemorrhagic infarction with subsequent ingrowth of transitional epithelium from the urethra producing re-epithelialization of glandular spaces along the residual coliagenous architecture. Conclusions: Accurate TRUS monitoring of prostate cryotherapy allows thorough yetcareful extension of the iceball through the posterior aspect of the prostate. Unique histologic changes may account for the unremarkable TRUS appearance following cryotherapy, as well as some of the benign, "atypical" glands seen on follow-up biopsies in humans.
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