Prostatic cyst is a benign condition forming fluid-filled cavities within the prostate gland and can develop through various etiological mechanisms. Retention cysts are the most common type, forming through accumulation of glandular secretions due to obstruction of prostatic ducts; they typically develop in the transition zone in the setting of benign prostatic hyperplasia (BPH). Cystic degeneration occurs due to necrotic/degenerative changes in the center of BPH nodules. Rarer types include mullerian duct cysts (midline, posterior), utricle cysts (dilatation of prostatic utricle), ejaculatory duct cysts, and congenital cysts. Prevalence is reported as 5-15% in MRI studies and increases with age. On mpMRI, prostatic cysts show markedly hyperintense fluid signal on T2-weighted sequences, hypointense on T1; no diffusion restriction on DWI (high ADC) and no wall enhancement or minimal thin wall enhancement on contrast-enhanced sequences. These findings are critically important in differentiating simple cyst from abscess and cystic degeneration from solid tumor. In PI-RADS v2.1, simple cysts are classified as PI-RADS 1 (definitely benign). Most prostatic cysts are clinically insignificant and detected incidentally; however, large cysts can cause bladder neck obstruction, hematospermia, or infertility due to ejaculatory duct obstruction.
Age Range
30-70
Peak Age
50
Gender
Male predominant
Prevalence
Uncommon
Prostatic cysts develop through three main pathophysiological mechanisms: (1) Retention cysts: adenomatous growth of BPH mechanically obstructs prostatic ducts, creating proximal secretion accumulation and ductal dilatation. The obstructed duct progressively expands and transforms into a cystic structure. Contents may be serous, proteinaceous, or mucinous. (2) Cystic degeneration: ischemic necrosis develops in the center of large BPH nodules due to vascular insufficiency. The necrotic area undergoes liquefaction forming a cystic cavity. Contents typically include hemorrhagic or proteinaceous debris. (3) Congenital/embryonal cysts: mullerian duct cysts develop from embryonal mullerian duct remnants, utricle cysts from congenital dilatation of prostatic utricle. On MRI, T2 hyperintensity reflects the long T2 relaxation time of free fluid within the cyst cavity — since water molecules can move freely within the cyst, spin-spin decoherence is slow and signal remains high. Absence of diffusion restriction on DWI (high ADC) indicates that cyst content is a low-viscosity fluid permitting free water diffusion — this finding provides definitive differentiation from viscous purulent material in abscess (diffusion restricted, low ADC). Absence of enhancement reflects that the cyst wall is avascular or minimally vascular.
The triple finding of marked T2 hyperintensity + high signal on ADC map (no diffusion restriction) + no wall enhancement on contrast-enhanced sequences is diagnostic for simple prostatic cyst. This triad definitively differentiates cyst from abscess (T2 hyperintense + low ADC + rim enhancement) and from cystic tumor (variable T2 + low ADC + solid enhancement).
Markedly hyperintense (bright) fluid signal is observed on T2-weighted sequences. In simple cysts, signal is homogeneous and bright like fluid; in cystic degeneration or hemorrhagic cyst, internal structure may be more heterogeneous. Cyst margins are sharp and smooth. Size may range from a few mm to 2-3 cm. Multiple cysts are common in BPH setting. Midline posterior cysts may represent mullerian duct cyst or utricle cyst.
Report Sentence
A [size] mm cystic lesion demonstrating hyperintense fluid signal on T2-weighted sequence is identified in the [location] of the prostate gland, consistent with simple cyst.
No diffusion restriction is observed in the cyst cavity on DWI. High signal on ADC map (high ADC values reflecting free water diffusion, typically >2.0 × 10⁻³ mm²/s) is obtained. Bright signal on DWI may be seen due to T2 shine-through but high signal on ADC confirms absence of true restriction. This finding is the most critical criterion providing definitive differentiation from prostatic abscess (DWI bright + ADC low).
Report Sentence
No diffusion restriction is detected in the cystic lesion on DWI with high signal on ADC map; this finding is consistent with simple cyst and abscess has been excluded.
No wall enhancement or minimal thin wall enhancement is observed on contrast-enhanced T1-weighted sequences. Simple cyst wall is thin (<1 mm) and avascular, showing no contrast uptake. This finding provides definitive differentiation from thick and intense rim enhancement in abscess. In cystic degeneration, the solid component of the BPH nodule may enhance but the cystic cavity does not enhance.
Report Sentence
No significant wall enhancement is observed on contrast-enhanced sequences, consistent with simple cyst.
Hypointense fluid signal is observed in simple cyst on T1-weighted sequences. Simple serous fluid has long T1 relaxation time and gives low signal on T1. T1 signal may be mildly increased in cysts with proteinaceous content (protein T1 shortening effect). In hemorrhagic cysts, marked T1 hyperintensity may be observed due to methemoglobin — in this case differentiation from post-biopsy hemorrhage is needed. Pre-contrast T1 sequence should always be evaluated.
Report Sentence
The cystic lesion shows hypointense signal on T1-weighted sequence, consistent with simple fluid content.
An anechoic (echo-free) or hypoechoic, well-defined cystic structure is observed within the prostate gland on TRUS. Posterior acoustic enhancement behind the cyst confirms fluid content. Simple cyst wall is thin and smooth. In the presence of internal septation or debris, complicated cyst should be considered. No vascularity is detected within the cyst on color Doppler US (avascular).
Report Sentence
A [size] mm anechoic, well-defined cystic structure with posterior acoustic enhancement is identified in the [location] of the prostate gland on TRUS, consistent with simple cyst.
Criteria
Cyst formed due to prostatic duct obstruction secondary to BPH. Most common in transition zone. Usually small (<1 cm). May be multiple.
Distinct Features
Most common type of prostatic cyst. Small cystic foci between or at the margins of BPH nodules. Bright on T2, hypointense on T1. Clinically insignificant. PI-RADS 1.
Criteria
Cystic cavity in the center of large BPH nodule due to ischemic necrosis and liquefaction. Usually >1 cm. Content may be proteinaceous or hemorrhagic.
Distinct Features
Central cystic area within BPH nodule. Cystic component hyperintense on T2, solid BPH component with variable signal. Surrounding BPH nodule may enhance, cystic cavity does not enhance. T1 signal may increase with proteinaceous/hemorrhagic content. PI-RADS 1-2.
Criteria
Mullerian duct cyst: midline, posterior, extending above verumontanum, may be large (up to 5 cm). Utricle cyst: originates from prostatic utricle, midline, smaller (<1 cm). Both have midline posterior localization.
Distinct Features
Midline posterior prostate localization — differentiated from retention cysts (TZ, bilateral) by localization. T2 hyperintense, T1 hypointense (simple) or T1 hyperintense (proteinaceous/hemorrhagic). Mullerian duct cyst may extend above the prostate. Utricle cyst is related to ejaculatory ducts and may cause fertility problems. Important in infertility workup.
Distinguishing Feature
In abscess, marked diffusion restriction (ADC low: 0.3-0.8) is present on DWI, while cyst has no diffusion restriction (ADC high: >2.0). Abscess shows thick rim enhancement while cyst wall does not enhance. Abscess is symptomatic with fever and pain; cyst is generally asymptomatic. Both may be hyperintense on T2 — differentiation is made by DWI/ADC and enhancement.
Distinguishing Feature
Solid BPH nodule shows heterogeneous, variable signal on T2, while cyst shows homogeneous hyperintense fluid signal on T2. BPH nodule shows enhancement while cyst does not enhance. On DWI, BPH may show partial restriction (stromal component), cyst shows no restriction. In cystic degeneration of BPH, solid and cystic components are seen together.
Distinguishing Feature
Seminal vesicle cyst is localized outside the prostate in the seminal vesicles — T2 hyperintense but tubular morphology of seminal vesicles is preserved. Prostatic cyst is localized within the prostate gland. Anatomic localization is determinant in differential diagnosis. Seminal vesicle cyst may cause ejaculatory duct obstruction and may be associated with infertility.
Distinguishing Feature
Ductal adenocarcinoma may contain cystic or papillary component in periurethral area but shows DWI restriction (ADC low) and enhancement in solid components. Simple cyst has no diffusion restriction and no enhancement. Ductal adenocarcinoma clinically presents with hematuria and obstructive urinary symptoms; simple cyst is generally asymptomatic. In the presence of mixed cystic-solid structure, ductal adenocarcinoma should be considered.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upThe vast majority of prostatic cysts are clinically insignificant and require no treatment. When simple cyst findings are detected on mpMRI (T2 hyperintense + ADC high + no enhancement), it is assessed as PI-RADS 1 and no additional workup or follow-up is needed. Clinical intervention is required for: (1) Large cyst causing bladder neck obstruction (>2-3 cm): transurethral drainage or marsupialization; (2) Infertility due to ejaculatory duct obstruction: transurethral resection (especially in midline cysts); (3) Recurrent hematospermia: cyst aspiration or surgery; (4) Infected cyst (abscess development): antibiotic therapy and drainage. In differential diagnosis, the most important differentiation should be made with abscess: no diffusion restriction in cyst (ADC high), marked restriction in abscess (ADC low). Proteinaceous or hemorrhagic cyst content can create atypical MR findings — clinical correlation and follow-up MRI may be needed.
Prostatic cysts are usually asymptomatic and discovered incidentally. Large cysts may cause bladder outlet obstruction or hemospermia. Treatment is only needed for symptomatic cysts (aspiration or marsupialization). There is no risk of malignant transformation.