Prostatitis is inflammation of the prostate gland, classified into four categories according to the NIH classification: acute bacterial, chronic bacterial, chronic pelvic pain syndrome (CPPS/chronic abacterial prostatitis), and asymptomatic inflammatory prostatitis. The most commonly encountered forms radiologically are acute bacterial prostatitis (NIH Category I) and chronic prostatitis (NIH Category II-III). On mpMRI, prostatitis is characterized by diffuse or focal T2 hypointensity in the peripheral and/or transition zone, wedge-shaped or striated enhancement pattern, and mild-to-moderate diffusion restriction. Prostatitis is the most common benign condition that can mimic prostate cancer — especially focal prostatitis can be confused with adenocarcinoma by showing focal T2 hypointensity and DWI restriction in the peripheral zone. PSA levels can be very elevated in acute prostatitis (>20 ng/mL) and mildly-moderately elevated in chronic prostatitis. Clinical correlation (fever, dysuria, pelvic pain, urine culture) is critical for diagnosis.
Age Range
20-60
Peak Age
40
Gender
Male predominant
Prevalence
Common
Acute bacterial prostatitis usually develops when gram-negative bacteria (E. coli, Klebsiella, Proteus) reach the prostate through the urethra or bloodstream. Bacterial invasion creates neutrophilic infiltration and edema — this inflammatory infiltration disrupts normal prostatic glandular architecture and leads to hypointense appearance on T2. Fluid-filled glandular lumens in normal PZ are filled with inflammatory cells, edema, and fibrosis — free water decreases and T2 relaxation time shortens. The wedge-shaped enhancement pattern results from inflammation spreading along periglandular vascular structures — following the arterial branching pattern. Diffusion restriction results from inflammatory cell infiltration narrowing the extracellular space and edema restricting water diffusion, but there is no dense cell packing as in adenocarcinoma, so DWI restriction is generally milder. In chronic prostatitis, fibrosis and glandular atrophy develop — this can cause persistent T2 hypointensity and may be indistinguishable from cancer even after biopsy. In non-granulomatous chronic prostatitis, lymphocytes and plasma cells predominate.
Wedge-shaped or striated enhancement pattern in the peripheral zone on DCE MRI is a finding specific to prostatitis. This pattern reflects inflammation spreading along the segmental arterial distribution of the prostate. Morphologically distinctly different from the focal, nodular, round/oval enhancement of adenocarcinoma. The base of the wedge is directed toward the prostatic capsule and the apex toward the center.
Diffuse, band-like, or wedge-shaped hypointensity is observed in the peripheral zone on T2-weighted images. In acute prostatitis, edema is prominent and hypointensity covers a broader area. In chronic prostatitis, focal or segmental hypointensity is more prominent due to fibrosis and glandular atrophy. Hypointensity tends to be bilateral and symmetric but focal, unilateral forms also exist — this form most closely mimics adenocarcinoma. In prostatitis, boundaries of the hypointense area are generally irregular and blurred, without the well-defined focal lesion appearance seen in adenocarcinoma.
Report Sentence
Diffuse/wedge-shaped T2 hypointensity is noted in the peripheral zone, which may be consistent with prostatitis in the clinical context; focal adenocarcinoma should be excluded.
Prostatitis shows wedge-shaped or striated enhancement pattern on DCE MRI. This pattern reflects inflammation spreading along the segmental arterial distribution of the prostate. Enhancement tends to be diffuse and symmetric. Enhancement is more prominent in acute prostatitis (increased vascular permeability) and milder in chronic prostatitis. Different from the focal, round/oval, nodular enhancement of adenocarcinoma. Striated enhancement indicates inflammation spreading along prostatic ducts.
Report Sentence
Wedge-shaped/striated enhancement pattern is noted in the peripheral zone on DCE series, consistent with prostatitis.
Prostatitis may show mild-to-moderate diffusion restriction on DWI. In acute prostatitis, DWI restriction may be more pronounced due to inflammatory edema and cell infiltration, potentially mimicking adenocarcinoma. In chronic prostatitis, DWI restriction is generally milder. ADC values are usually >900 × 10⁻⁶ mm²/s, which may help distinguish from adenocarcinoma (<800). However, ADC values can drop to adenocarcinoma levels in acute prostatitis — in this case, clinical correlation (fever, symptoms) and follow-up MR after treatment should confirm the diagnosis.
Report Sentence
Mild-to-moderate diffusion restriction is noted in the peripheral zone on DWI with ADC values above the adenocarcinoma threshold (>900 × 10⁻⁶ mm²/s); prostatitis should be primarily considered.
Prostatitis usually shows normal T1 signal on T1-weighted images. In acute prostatitis, inflammatory stranding in periprostatic fat may be seen — appearing as periprostatic signal increase on T1 fat-sat sequences. If abscess develops, a collection with T1 hypointense center and peripheral ring enhancement is observed. The most important role of T1 in prostatitis is exclusion of hemorrhage: post-biopsy hemorrhage shows hyperintense signal on T1 (methemoglobin), while prostatitis has normal T1. mpMRI is recommended at least 6-8 weeks after biopsy — hemorrhage can mask prostatitis and cancer.
Report Sentence
Inflammatory stranding is noted in periprostatic fat on T1-weighted images without T1 hyperintense hemorrhage; consistent with acute prostatitis.
Acute prostatitis shows periprostatic and intraglandular increased vascularity on TRUS Doppler. Inflammatory hyperemia is observed as increased vascular signal on color Doppler. Diffuse glandular swelling and hypoechoic areas may be seen. If abscess develops, an avascular (no Doppler signal) fluid collection surrounded by hypervascular rim is observed. Power Doppler is more sensitive than color Doppler for detecting low-flow inflammatory vascularity. Prostatic calcifications (common in chronic prostatitis) may also be seen as hyperechoic foci on TRUS.
Report Sentence
Diffuse increased vascularity is noted in the prostate gland on TRUS Doppler with periprostatic inflammatory changes; consistent with acute prostatitis.
Criteria
Bacterial infection, acute onset, positive urine culture
Distinct Features
Fever, dysuria, perineal pain, very high PSA (>20). On MR diffuse edema, prominent enhancement, DWI restriction. Risk of abscess development. Pyuria and bacteriuria. Resolution with antibiotic therapy in 4-6 weeks.
Criteria
Recurrent urinary infection, symptoms >3 months
Distinct Features
Focal or diffuse T2 hypointensity (fibrosis), mildly elevated PSA, prostatic calcifications common. MR findings may mimic focal adenocarcinoma — biopsy may be needed.
Criteria
Pelvic pain >3 months, no bacteria on culture, inflammatory (IIIA) or non-inflammatory (IIIB)
Distinct Features
MR findings usually normal or showing mild nonspecific changes. PSA normal or mildly elevated. Diagnosis usually clinical and by exclusion. Main role of imaging is to exclude cancer.
Distinguishing Feature
PZ adenocarcinoma shows focal, round/oval, well-defined T2 hypointense lesion with marked DWI restriction (ADC <800). Prostatitis shows diffuse/wedge-shaped hypointensity with blurred borders. DCE is focal and nodular in adenocarcinoma, wedge-shaped/striated in prostatitis. PSA kinetics is distinguishing: decreases with treatment in prostatitis, persistent in cancer.
Distinguishing Feature
Granulomatous prostatitis shows focal, nodular T2 hypointensity and marked DWI restriction — very similar to cancer unlike non-granulomatous prostatitis. History of BCG treatment or systemic granulomatous disease is a distinguishing clue. Biopsy is usually required.
Distinguishing Feature
Prostate abscess shows T2 hyperintense, T1 hypointense fluid collection with marked DWI restriction (pus) and surrounding rim enhancement. Prostatitis has no fluid collection, diffuse pattern predominates. Abscess development is a complication of acute prostatitis.
Distinguishing Feature
Atrophy can show T2 hypointensity in PZ but does not show DWI restriction or enhancement increase. Atrophy is usually bilateral and symmetric with no clinical symptoms and normal PSA.
Urgency
urgentManagement
medicalBiopsy
Not NeededFollow-up
3-monthAcute bacterial prostatitis requires antibiotic treatment (fluoroquinolone or TMP-SMX, 4-6 weeks). Biopsy is contraindicated in the acute phase — risk of bacteremia and sepsis. PSA elevation is related to infection and follow-up PSA is recommended after treatment. Biopsy should be considered if PSA does not return to normal after treatment. Biopsy is recommended if a suspicious lesion persists on mpMRI despite treatment. Percutaneous or transrectal drainage may be needed if abscess develops. Focal prostatitis is assessed as PI-RADS 3 — biopsy decision is made with PSA density and clinical risk.
Prostatitis is an important diagnostic pitfall on mpMRI as a cancer mimicker. Acute bacterial prostatitis is treated with antibiotics. Prostatitis should be excluded before biopsy to avoid unnecessary procedures. PSA elevation occurs in both prostatitis and cancer; clinical correlation is essential.