Multi-parametric MRI Findings of Granulomatous Prostatitis Developing After Intravesical Bacillus Calmette-guérin Therapy

Purpose: To evaluate the multi-parametric MRI (mpMRI) findings in patients with biopsy-proven granulomatous prostatitis and prior Bacillus Calmette-Guérin (BCG) exposure.

Materials And Methods: MRI was performed in six patients with pathologically proven granulomatous prostatitis and a prior history of bladder cancer treated with intravesical BCG therapy. Multi-parametric prostate MRI images were recorded on a GE 750W or Philips Achieva 3.0 Tesla MRI scanner with high-resolution, small-field-of-view imaging consisting of axial T2, axial T1, coronal T2, sagittal T2, axial multiple b-value diffusion (multiple values up to 1200 or 1400), and dynamic contrast-enhanced 3D axial T1 with fat suppression sequence.

Results: Two different patterns of MR findings were observed. Five of the six patients had a low mean ADC value <1000 (decreased signal on ADC map images) and isointense signal on high-b-value imaging (b = 1200 or 1400), consistent with nonspecific granulomatous prostatitis. The other pattern seen in one of the six patients was decreased signal on the ADC map images with increased signal on the high-b-value sequence, revealing true restricted diffusion indistinguishable from aggressive prostate cancer. This patient had biopsy-confirmed acute BCG prostatitis.

Conclusions: Our study suggests that patients with known BCG exposure and PI-RADS v2 scores ≤3, showing similar mpMRI findings as demonstrated, may not require prostate biopsy.