Histologic characterization of the post-radiation urethral stenosis in men treated for prostate cancer.

PURPOSE: To evaluate histological changes in stenotic urethral tissue post-radiation therapy. Treatment of prostate cancer by radiation therapy carries a risk of off-target injury to the membranous urethra causing urethral stenosis. Limited characterization of post-radiation urethral stenosis exists in the literature. We hypothesize that specific histopathologic parameters distinguish this stricture etiology.

METHODS: Eighty-two consecutive patients with membranous urethral stenosis underwent urethroplasty between 2013 and 2018. Seventy specimens (86.4%) were available for evaluation: 51 from patients without radiation exposure and 19 from patients with history of radiation therapy for prostate cancer. All specimens were reviewed by a pathologist blinded to patient/stricture information. Histological scoring system was used for the quantification of collagen density, collagen organization, hyalinized fibrosis, vascular density, spindle-cell change, necrosis, hemorrhage, fat entrapment, vacuolation, acute and chronic inflammation, and foreign-body giant cells. Differences in histologic outcomes between groups were statistically analyzed.

RESULTS: Post-radiation specimens had a higher collagen density (p = 0.01), higher collagen organization (p = 0.001), increased hyalinized fibrosis (p = 0.03), fat entrapment (p = 0.005) and spindle cell change (p = 0.005) when compared to membranous specimens without prior exposure to radiation. Post-radiation specimens also had a significantly decreased vascularity compared to specimens of non-radiated etiology (p = 0.0005). Fibrous connective tissue degenerative change with vacuolation was pronounced in post-radiation specimens and seldom seen in those without radiation (p = 0.0001).

CONCLUSIONS: Membranous urethral stenosis following radiation demonstrates specific histologic characteristics including vascular loss and increased scarring (collagen density, organization). This histologic grading system may be used in grading severity of radiation damage, and conceivably adopted for correlation with clinical outcomes.