MRI findings of granulomatous prostatitis induced by intravesical Bacillus Calmette-Guérin treatment for bladder cancer: a comparison with prostate cancer.

[PURPOSE] To characterize the magnetic resonance imaging (MRI) features of Bacillus Calmette-Guérin (BCG)-induced granulomatous prostatitis (GP) and to identify key imaging findings for differentiating it from prostate carcinoma (PCa).

[MATERIALS AND METHODS] This retrospective study included 11 patients with pathologically confirmed BCG-induced GP and a comparison group of 88 patients (90 lesions) with PCa. Two radiologists retrospectively evaluated MRI findings. Qualitative analysis included lesion location, morphology, and signal intensity (SI) patterns on T1-weighted (T1WI), T2-weighted (T2WI), and diffusion-weighted imaging (DWI). Quantitative analysis compared lesion size, apparent diffusion coefficient (ADC) values, and T1WI SI ratios to both muscle and background prostate. Statistical comparisons were made using Fisher's exact test for qualitative data and the Mann-Whitney U test for quantitative data.

[RESULTS] Hyperintensity on T1WI was significantly more frequent in GP (100%) than in PCa (11%; p < 0.001). The lesion-muscle SI ratio on T1WI was also significantly higher in GP (p < 0.001), whereas the lesion-background SI ratio was not (p = 0.054). Furthermore, a diffuse morphology was significantly more common in GP (45%) compared to PCa (12%; p = 0.014), and the distribution of lesion locations also differed significantly (p = 0.041). No significant differences were found in lesion size, SI on T2WI or DWI and ADC values.

[CONCLUSION] Some PCa exhibit similar imaging findings to GP, but T1 hyperintensity and a diffuse morphology are characteristic features of GP.