Correlation Between the Natural Course and Magnetic Resonance Imaging Features of Bacillus Calmette-Guérin-Related...

To evaluate magnetic resonance imaging features and the natural course of granulomatous prostatitis after intravesical Bacillus Calmette-Guérin therapy in patients with bladder cancer.

Using a radiologic report keyword search program, data were collected from magnetic resonance images between March 2018 and August 2023. A total of 241 baseline or follow-up magnetic resonance images of 64 patients with pathologically or clinically confirmed Bacillus Calmette-Guérin-related granulomatous prostatitis were retrospectively included. We investigated intravesical Bacillus Calmette-Guérin history, lesion size changes, and serum prostate-specific antigen changes through a chart review. Lesion imaging features were assessed on T1-. T2-, diffusion-, and contrast-enhanced T1-weighted images and classified based on enhancement degree and presence of diffusion restriction.

The completely improved group (n = 12), incompletely improved group (n = 26), and recurrent inflammation group (n = 13) were identified according to temporal magnetic resonance imaging changes of granulomatous prostatitis. Patients who underwent radical cystectomy or were lost to follow-up were excluded due to unknown outcomes (n = 13). Among 64 patients, subtle increased T1 signal intensity with granulomatous inflammation was observed in 57 (89.1%). The baseline prostate-specific antigen level in the recurrent inflammation group was 2.00 ± 1.26 ng/mL, which was higher than the 1.0-1.1 ng/mL levels in the other groups (P = 0.050). Even if the lesion completely improved on magnetic resonance imaging, the serum prostate-specific antigen level increased by approximately 2.0 times compared to the baseline level. Lesion peak size (26.0 ± 15.0 mm) in the incompletely improving group was significantly larger than that in the other groups (14.8 ± 5.8 and 17.0 ± 9.1 mm) (P = 0.006). Among the 77 initial magnetic resonance images, type A (n = 30, strong enhancement and diffusion restriction), type B (n = 25, rim enhancement with diffusion restriction), and mixed type (n = 19) were the most common. In the last 50 magnetic resonance images, type C (n = 34; no enhancement or diffusion restriction) was predominant.

In patients who underwent intravesical Bacillus Calmette-Guérin therapy, bladder magnetic resonance imaging frequently revealed subtle T1-hyperintense lesion in the prostate with diffuse or rim-like enhancement accompanied by markedly restricted diffusion, which is highly suggestive of Bacillus Calmette-Guérin-related granulomatous prostatitis and tends to spontaneously regress on follow-up imaging. Even with radiological improvement, prostate-specific antigen levels may remain elevated and should not be mistaken for malignancy.