Teaching Case

A 52-year-old male patient, with previous bladder urothelial carcinoma treated with intravesical Bacillus Calmette-Guérin (BCG), presented a prostatic lesion in a routine computed tomography scan. PSA levels were normal, patient was asymptomatic and digital rectal examination was unsuspicious.

Magnetic resonance imaging (MRI) was requested, which was followed by prostate biopsy.

Multiparametric MRI (mpMRI) was performed on a 1.5 Tesla magnet, using a protocol with T2-weighted images (T2W), diffusion-weighted images (DWI), apparent diffusion coefficient (ADC) and dynamic contrast enhancement (DCE).

A well-defined nodule was identified in the right posterior peripheral zone (PZ), extending from the midgland to the apex, measuring 27 mm in its longest axis. It presented homogeneous low signal intensity on T2W images, marked high signal intensity on b1400 DWI and marked low signal in ADC map imaging. DCE revealed early and prolonged thin rim enhancement, with no central enhancement.

The prostatic capsule was preserved. No suspicious pelvic lymph nodes or focal bone lesions were detected. The bladder and seminal vesicles were normal. The prostatic volume was 52 mL.

Final PI-RADS score was 5 (very high probability of clinically significant cancer) and a biopsy was performed. Histologic analysis reported nonspecific granulomatous prostatitis (GP), with no malignant findings.

Background

GP is a rare benign inflammatory condition of the prostate, with an incidence of 1-3% in prostate biopsies [1-3]. It can be idiopathic, infectious, iatrogenic or associated with systemic granulomatosis [1-4]. Previous treatment for bladder transitional cell carcinoma with intravesical BCG is a common infectious cause [2].

GP occurs due to blockage of the prostatic ducts, with stasis of secretions and epithelial disruption, being histologically characterized by the presence of granulomas with aggregation of macrophages and a collar of mononuclear leukocytes and plasma cells [1-3,6]. Diagnosis relies on biopsy and compatible clinical context, such as treatment with intravesical BCG [4].

Clinical perspective

Patients with GP may present lower urinary tract symptoms such as hematuria, urgency or urinary frequency, or be asymptomatic, as in the present case [3-5]. On digital rectal examination, the prostate may be hardened and painful [3,4].

GP can also present normal to elevated PSA levels, thus clinically mimicking prostate carcinoma [1,4,5].

Imaging perspective

MRI presentation of GP is variable, more commonly showing a PZ lesion with low-intensity signal on T2W images, high intensity on DWI, low intensity on ADC map and moderate internal enhancement or early and prolonged rim enhancement on DCE [1-5]. Rim enhancement is a reflex of granuloma caseation and might not be present in early stages of GP [2]. In fact, two MRI patterns can occur a diffuse tumour-like lesion, or a focal nodule representing caseous necrosis [2,6].

Consequently, GP lesions are often classified as PI-RADS 4 or 5, highly suspicious for prostate carcinoma, so biopsy is often recommended [2,3]. However, presence of early and prolonged rim enhancement, with no internal enhancement, suggests a longstanding GP lesion with caseous necrosis, uncommon in prostate carcinoma [4,5].

Outcome

GP does not have a standardized medical treatment and usually resolves naturally [3]. However, especially in cases of BCG-induced GP, symptomatic patients should receive isoniazid and rifampicin for 3 months [4]. Follow-up imaging with MRI is also recommended, documenting decrease in size over time, which does not occur with prostate carcinoma [4,5]. In the present case, no treatment was proposed and the patient is due for annual reassessment with MRI, as well as blood tests after 6 months, including PSA levels.

Take-Home Message / Teaching Points

BCG-induced granulomatous prostatitis is a rare benign inflammatory condition, which can mimic prostate carcinoma, both clinically and with MRI.

Diagnosis relies on histological examination and compatible clinical context of previous intravesical therapy.

Distinguishing BCG-induced GP from prostate carcinoma on MRI is challenging, but features such as early and prolonged rim enhancement are more suggestive of GP.

Written informed patient consent for publication has been obtained.