Prostatic leiomyoma is a rare benign mesenchymal tumor originating from smooth muscle cells of the prostate. It constitutes less than 0.1% of all prostate neoplasms. It presents as a well-circumscribed, encapsulated, homogeneous solid mass. Histologically, it shows no atypia, necrosis, or increased mitotic activity — this feature differentiates from leiomyosarcoma. On mpMRI, it appears as a well-defined mass with low signal on T2 (smooth muscle tissue), isointense on T1, and homogeneous enhancement. In PI-RADS v2.1, it is evaluated as a stromal lesion — may mimic prostate adenocarcinoma but well-circumscription and homogeneous structure suggest benignity. Treatment is usually surgical excision or conservative follow-up.
Age Range
40-70
Peak Age
55
Gender
Male predominant
Prevalence
Rare
Prostatic leiomyoma originates from smooth muscle cells (leiomyocytes) in the stromal component of the prostate. The fibromuscular stroma of the prostate expresses androgen receptors — whether leiomyoma grows under androgen influence is debatable, but regression with antiandrogen therapy has been reported in some cases. The tumor is well-circumscribed and encapsulated, not invading surrounding tissue — shows expansile growth. Histologically, mature smooth muscle fibers are arranged as spindle-shaped cells surrounded by interstitial collagen. On imaging, it shows low T2 signal because smooth muscle tissue is a dense fibrous structure with low free water content — short T2 relaxation time. It shows homogeneous enhancement because smooth muscle tissue is vascularized yet contains no necrosis or hemorrhage. This homogeneous structure and well-circumscription differentiate from adenocarcinoma (heterogeneous, invasive) and leiomyosarcoma (containing necrosis, hemorrhage).
Characteristic MRI appearance of prostatic leiomyoma: markedly low signal on T2 (smooth muscle tissue), well-defined borders (encapsulated benign tumor), homogeneous enhancement (regular vascularity, no necrosis). This triple combination differentiates from prostate cancer (heterogeneous, irregularly bordered) and leiomyosarcoma (necrosis, hemorrhage). Based on the same principles as MRI appearance of uterine leiomyomas — universal MRI signature of smooth muscle-origin tumors.
Markedly hypointense, well-circumscribed, homogeneous solid mass on T2-weighted images. Smooth borders and capsule are observed. Clearly separated from surrounding prostate tissue. T2 hypointensity is the most distinctive MRI finding across all modalities — reflects the dense fibrous structure of smooth muscle tissue.
Report Sentence
Markedly hypointense, well-circumscribed, encapsulated, homogeneous solid lesion in the prostate on T2-weighted images, consistent with leiomyoma.
Isointense or mildly hypointense to prostate tissue on T1-weighted images. Homogeneous signal — no hemorrhage or fat component. T1 signal is not discriminatory for leiomyoma diagnosis but confirms absence of hemorrhage, necrosis, or fat content.
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Lesion showing isointense signal to prostate tissue on T1-weighted images.
Homogeneous, moderate enhancement on contrast-enhanced sequences. No necrosis or non-enhancing areas. Smooth capsular enhancement may be observed. Homogeneous enhancement pattern differentiates from malignant tumors (heterogeneous, rim enhancement).
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Lesion showing homogeneous enhancement on contrast-enhanced sequences with no necrosis or heterogeneous area.
May show mild-moderate diffusion restriction on DWI — ADC value higher than adenocarcinoma (usually >1.0 × 10⁻³ mm²/s). This restriction results from tight packing of smooth muscle fibers, not high cellularity. Marked restriction seen in adenocarcinoma (ADC <0.8) is not seen in leiomyoma.
Report Sentence
Lesion showing mild diffusion restriction and intermediate ADC value on DWI, consistent with smooth muscle tumor; marked restriction at adenocarcinoma level is not observed.
Well-defined, homogeneous hypoechoic solid lesion on TRUS. Smooth borders and posterior acoustic shadowing may be seen (dense smooth muscle tissue). Differentiated from prostate cancer by well-circumscription and homogeneous structure but TRUS alone does not provide definitive diagnosis — MRI and biopsy are needed.
Report Sentence
Well-defined, homogeneous hypoechoic solid lesion in the prostate on TRUS; leiomyoma should be considered in differential diagnosis; MRI characterization is recommended.
Criteria
Located within prostate parenchyma. More common type. Grows in TZ or stromal area. May be confused with BPH nodules.
Distinct Features
Intraprostatic, may mimic BPH, within capsule, stromal location
Criteria
Leiomyoma growing outside prostate capsule in periprostatic area. Rarer. May originate from bladder neck, rectoprostatic area. May reach larger sizes because not confined by prostate capsule.
Distinct Features
Extraprostatic, large size potential, extracapsular, bladder/rectum compression
Criteria
Leiomyoma attached to prostate or bladder neck by a stalk, extending into lumen. Very rare. May prolapse into urethra or bladder lumen causing urinary obstruction. Treated with transurethral resection.
Distinct Features
Stalk-attached, intraluminal, obstruction risk, TUR indication
Distinguishing Feature
BPH nodules are usually located in TZ, have variable T2 signal (may have hyperintense areas due to glandular component), multiple, and associated with enlarged prostate. Leiomyoma is solitary, homogeneously T2 hypointense, and can be found in any zone. Erased charcoal sign and organized chaos pattern in BPH are not seen in leiomyoma.
Distinguishing Feature
TZ adenocarcinoma has irregular borders, T2 hypointense, heterogeneous (erased charcoal sign negative), and shows marked diffusion restriction (ADC <0.8). Leiomyoma is well-circumscribed, encapsulated, homogeneous, and ADC value is higher (>1.0). Invasive growth pattern (lenticular) and erased charcoal sign favor adenocarcinoma.
Distinguishing Feature
Prostate stromal tumor (STUMP/phyllodes-like) is larger, may contain cystic-solid components, and may show heterogeneous structure. Leiomyoma is entirely solid, homogeneous, and contains no cystic component. Stromal tumors carry more aggressive behavior potential and may recur.
Urgency
routineManagement
surgicalBiopsy
NeededFollow-up
6-monthProstatic leiomyoma is a rare benign tumor and definitive diagnosis is usually made by histopathological examination of biopsy/excision material. Although mpMRI findings may suggest leiomyoma, MR-guided biopsy is recommended since adenocarcinoma is in the differential diagnosis. Small asymptomatic lesions can be followed with PSA monitoring and MRI. Symptomatic lesions (urinary obstruction, growth) are treated with TUR or open prostatectomy. In PI-RADS v2.1, T2 hypointense + diffusion-restricting lesion may score PI-RADS 3-4 — biopsy may be needed even when benign stromal lesion is suspected.
Prostatic leiomyoma is a rare but benign tumor. It may cause lower urinary tract symptoms. Definitive diagnosis requires histopathological examination of biopsy or resection material. Malignant transformation (leiomyosarcoma) is extremely rare. Treatment is surgical in symptomatic patients.