Granulomatous prostatitis (GP) is a rare inflammatory condition characterized by granuloma formation in the prostate gland that closely mimics high-grade prostate cancer on mpMRI. The most common cause is BCG (Bacillus Calmette-Guérin)-related GP developing after intravesical BCG immunotherapy for bladder cancer — occurring in 1-3% of patients receiving BCG therapy. Other causes include non-specific (idiopathic) GP, systemic granulomatous diseases (sarcoidosis, Wegener's granulomatosis), post-surgical foreign body reaction, and tuberculosis. On mpMRI, it appears as a focal, hypointense lesion with marked DWI restriction in the peripheral zone — this appearance cannot be reliably distinguished from PI-RADS 4-5 prostate cancer. Definitive diagnosis is made by biopsy: histologically, epithelioid histiocytes, giant cells (Langhans type), caseous or non-caseous necrosis, and lymphocytic infiltration are seen. PSA levels can be elevated (typically 4-15 ng/mL) and digital rectal examination may reveal induration or nodularity — both findings mimicking cancer.
Age Range
40-70
Peak Age
55
Gender
Male predominant
Prevalence
Uncommon
Granulomatous prostatitis involves granuloma formation in prostate tissue as a result of T-cell mediated (Type IV) delayed hypersensitivity reaction. In BCG-related GP, live attenuated Mycobacterium bovis BCG strain instilled into the bladder passes to the prostate through prostatic ducts and triggers chronic granulomatous inflammation. Macrophages phagocytose mycobacterial antigens but cannot fully digest them — transforming into epithelioid histiocytes and forming Langhans-type giant cells. Granulomas destroy normal prostate glandular architecture and cause low signal intensity on T2 — glandular lumens are filled with granulomatous tissue, free water decreases. Marked restriction on DWI results from dense cell packing within granulomas (histiocytes, lymphocytes, plasma cells, fibroblasts) — this cell density resembles adenocarcinoma cell density and the degree of diffusion restriction is similar. Central hyperintensity on T2 can be seen with caseous necrosis. This pathophysiological similarity is the fundamental reason GP cannot be distinguished from cancer on MR.
Focal lesion in peripheral zone that is T2 hypointense, shows marked restriction on DWI, and early enhancement on DCE — indistinguishable from PI-RADS 4-5 cancer. The diagnostic key is history of BCG immunotherapy. Without this clinical information, GP is assessed as high-grade cancer until biopsy. Biopsy is mandatory even with BCG history in the presence of PI-RADS 4-5 lesion — GP can coexist with cancer.
A focal, well or poorly circumscribed hypointense lesion is observed in the peripheral zone on T2-weighted images — this appearance closely mimics prostate adenocarcinoma. Normal glandular architecture has been destroyed by granulomatous inflammation and replaced by granulomatous tissue. Lesion size is variable (from 5 mm to >20 mm). Central T2 hyperintense area may be seen with caseous necrosis — this finding suggests GP rather than cancer but is not a reliable differentiating criterion. Multifocal involvement is more common in BCG-related GP. Lesion morphology is indistinguishable from adenocarcinoma: may be round, oval, or irregular shaped.
Report Sentence
A ___ mm focal T2 hypointense lesion is noted in the peripheral zone, indistinguishable from adenocarcinoma on MR; considering history of BCG treatment, granulomatous prostatitis should be considered, biopsy is recommended.
The GP lesion shows markedly hyperintense signal at high b-value on DWI with low values on ADC map (ADC typically 600-900 × 10⁻⁶ mm²/s). This DWI pattern is indistinguishable from high-grade prostate cancer (Gleason 4+3 or 4+4). Dense cellular infiltration within granulomas (histiocytes, lymphocytes, giant cells) narrows the extracellular space and restricts water diffusion — mechanistically similar to dense tumor cell packing in adenocarcinoma. DWI findings alone cannot differentiate GP from cancer — biopsy is mandatory.
Report Sentence
Marked diffusion restriction is noted in the peripheral zone lesion on DWI (ADC: ___ × 10⁻⁶ mm²/s), indistinguishable from adenocarcinoma; possibility of granulomatous prostatitis should be considered and biopsy recommended.
The GP lesion usually shows early and intense enhancement on DCE MRI — mimicking adenocarcinoma. Increased vascular permeability and neovascularity (granulation tissue) in granulomatous inflammation produces focal enhancement. Enhancement pattern may be homogeneous or heterogeneous. With caseous necrosis, non-enhancing central area (necrotic center) and surrounding rim enhancement may be seen — this pattern suggests abscess but can also be seen in necrotic tumor. DCE findings are also not distinguishing from cancer.
Report Sentence
Early and intense enhancement is noted in the peripheral zone lesion on DCE series, indistinguishable from adenocarcinoma; histological verification by biopsy is required.
On TRUS, the GP lesion appears as a hypoechoic nodule or diffuse hypoechoic area in the peripheral zone — ultrasonographically indistinguishable from adenocarcinoma. The lesion may have irregular borders and show increased Doppler vascularity. TRUS-guided biopsy is required for diagnosis of GP — MR-TRUS fusion biopsy is recommended. Prostatic calcifications may be common in patients who received BCG treatment. Prostate dimensions may be normal or mildly increased.
Report Sentence
A hypoechoic lesion is noted in the peripheral zone on TRUS, indistinguishable from adenocarcinoma; considering BCG history, histological diagnosis should be established with MR-TRUS fusion-guided biopsy.
GP cannot be directly detected on CT but associated findings can be evaluated. Prostatic calcifications, prostate enlargement, and periprostatic inflammatory changes may be seen in chronic granulomatous inflammation. In BCG-related GP, concurrent bladder pathology (bladder cancer follow-up findings, post-TURBT changes) is evaluated. CT can be used for staging purposes to exclude lymph node and bone metastases — especially when biopsy results are equivocal.
Report Sentence
Calcifications and mild enlargement are noted in the prostate on CT, possibly consistent with chronic inflammatory process; mpMRI is recommended for primary lesion characterization.
Criteria
Caseous or non-caseous granulomas developing after intravesical BCG treatment for bladder cancer
Distinct Features
Most common cause. Develops 1-12 months after BCG treatment. May be positive on AFB (acid-fast bacilli) stain. Can be asymptomatic or show LUTS. May be incidentally detected on bladder cancer follow-up MRI. Anti-tuberculosis treatment may be needed.
Criteria
Non-caseous granulomas developing without known etiology, negative AFB and cultures
Distinct Features
Second most common type. Autoimmune reaction against prostatic secretions is suspected. No caseous necrosis. Usually seen in older men (60-70 years). Treatment: NSAIDs or corticosteroids.
Criteria
Mycobacterium tuberculosis infection, caseous necrosis, positive AFB or PCR
Distinct Features
More common in endemic areas. Usually part of genitourinary TB (kidney, epididymis may be co-involved). Caseous necrosis — central T2 hyperintensity on MR. Calcifications common (dystrophic calcification). Anti-tuberculosis treatment (6-9 months) required.
Criteria
Prostatic involvement developing in setting of sarcoidosis, Wegener's granulomatosis, or other systemic granulomatous disease
Distinct Features
Rare. Systemic disease findings (lung, skin, joint involvement) are present. Non-caseous granulomas (sarcoidosis), necrotizing vasculitis (Wegener's). Elevated ACE (sarcoidosis), positive c-ANCA (Wegener's). Systemic treatment (corticosteroids, immunosuppressants) required.
Distinguishing Feature
PZ adenocarcinoma CANNOT be reliably distinguished from GP on MR — both conditions show focal T2 hypointensity, marked DWI restriction, and early DCE enhancement. Differential relies on clinical information: BCG history, systemic granulomatous disease. Definitive diagnosis is by biopsy. GP and cancer can coexist — targeted biopsy from the lesion is critical.
Distinguishing Feature
Non-granulomatous prostatitis generally shows diffuse/wedge-shaped T2 hypointensity and striated enhancement — different from GP's focal, nodular appearance. DWI restriction in non-granulomatous prostatitis is milder (ADC >900). GP shows focal and marked restriction, resembling cancer. Clinical findings also differ: fever and dysuria are prominent in acute prostatitis, GP may be mild or asymptomatic.
Distinguishing Feature
Prostate abscess shows T2 hyperintense fluid collection, rim enhancement, and marked DWI restriction (pus content). GP appears as a solid lesion without fluid-filled cavity like abscess. However, GP with caseous necrosis may show central liquefaction and becomes difficult to distinguish from abscess — AFB staining and culture are distinguishing in this case.
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
3-monthDefinitive diagnosis of GP is by biopsy — biopsy is mandatory since MR findings are indistinguishable from cancer. In BCG-related GP, treatment is determined by symptom severity: asymptomatic → surveillance, symptomatic → fluoroquinolone (6-12 weeks) and/or anti-tuberculosis treatment (isoniazid + rifampicin), severe systemic symptoms → anti-tuberculosis treatment mandatory. Close PSA and MR follow-up is recommended even in patients whose biopsy shows GP, due to the possibility of concurrent cancer. Re-biopsy is needed if PSA does not decrease with follow-up after treatment. Lesion regression or disappearance on follow-up mpMRI supports GP diagnosis.
Granulomatous prostatitis is one of the most important mimickers of prostate cancer. In patients with BCG therapy or TB history, this diagnosis should be considered for PI-RADS 4-5 lesions. Definitive diagnosis requires targeted biopsy. Treatment is directed at the underlying cause (anti-tuberculosis therapy, steroids, or observation).