Adenomatoid tumor is the most common benign tumor of the paratesticular region, constituting approximately 30% of all paratesticular neoplasms. It originates from mesothelium (tunica vaginalis, tunica albuginea, epididymis). Most commonly located in the epididymal tail (cauda) or on the tunica albuginea. Occurs in men aged 20-50 years. On ultrasonography, it generally appears as a well-defined, homogeneous, hypoechoic or isoechoic solid nodule — usually 2-5 cm in diameter. Typically presents as a painless, palpable mass. There is NO malignancy potential and treatment can be conservative; excision is performed when diagnosis is uncertain. Bilateral or intratesticular location is very rare. On CT, appears as a well-defined, mildly enhancing paratesticular mass. Shows variable signal on T2 MRI. Differential diagnosis includes epididymitis, spermatocele, epidermal inclusion cyst, and leiomyoma.
Age Range
20-60
Peak Age
35
Gender
Male predominant
Prevalence
Uncommon
Adenomatoid tumor is a benign neoplasm of mesothelial origin. Histologically, it may show epithelioid (adenoid), angiomatoid, solid, and cystic patterns. Tumor cells express mesothelial markers (calretinin, WT1, CK5/6, D2-40) — this proves mesothelial origin. Growth pattern is slow and expansile; encapsulated or semi-encapsulated without invasion of surrounding tissue. The hypoechoic/isoechoic appearance on ultrasonography reflects the uniform tissue composition (epithelioid cells + fibrous stroma) — dense stroma is echogenic, loose stroma and cystic spaces create the hypoechoic component. The well-defined capsule reflects the tumor's pushing growth pattern — no aggressive invasive growth. Variable T2 signal on MRI depends on histological variants (epithelioid vs solid vs cystic) — increased cystic component increases T2 hyperintensity.
Well-defined, hypoechoic/isoechoic, solid, avascular nodule in paratesticular region (epididymis/tunica albuginea) + normal testicular parenchyma = adenomatoid tumor. Extratesticular location + low vascularity strongly supports benign nature.
On B-mode ultrasonography, adenomatoid tumor appears as a well-defined, homogeneous, hypoechoic or isoechoic solid nodule in the paratesticular region (most commonly epididymal tail or on tunica albuginea). The nodule is usually 2-5 cm in diameter, oval or round in shape. Internal structure is homogeneous — calcification, necrosis, or cystic component are generally absent. Testicular parenchyma appears normal. Tumor margins are clearly delineated — no infiltrative growth. Stretching of the tunica albuginea may be seen with large lesions.
Report Sentence
A well-defined, homogeneous, hypoechoic/isoechoic solid nodule measuring approximately ___ mm is seen at the right/left epididymal tail/tunica albuginea level; testicular parenchyma is normal.
On color Doppler, adenomatoid tumor shows avascular or hypovascular appearance — minimal or no internal vascularity is identified. This finding differs significantly from increased vascularity in malignant paratesticular tumors (rhabdomyosarcoma, leiomyosarcoma). Minimal peripheral vascularity may originate from capsular vessels, but internal flow is absent or minimal. Doppler finding supports the benign nature.
Report Sentence
No internal vascularity is identified in the paratesticular nodule on color Doppler; avascular/hypovascular pattern is consistent with benign nature.
On T2-weighted MR images, adenomatoid tumor shows variable signal — depending on histological variant. Epithelioid/cystic variant appears hyperintense on T2 (due to cystic spaces), solid/fibrous variant appears isointense to mildly hypointense. Generally isointense to muscle on T1. Shows mild-to-moderate enhancement on contrast-enhanced series. Well-defined capsule may show smooth enhancement. No restricted diffusion expected on DWI (low cellularity). MRI is complementary to US for intratesticular/extratesticular differentiation and tumor-testis relationship assessment.
Report Sentence
On MRI, the paratesticular mass shows ___ signal on T2, isointense on T1, with mild enhancement on contrast-enhanced series; no restricted diffusion is identified.
On CT, adenomatoid tumor appears as a well-defined, homogeneous, soft tissue density mass in the paratesticular region. Shows mild-to-moderate enhancement. No calcification, necrosis, or invasion findings. No inguinal or retroperitoneal lymphadenopathy. CT is generally not the primary imaging modality (US preferred) but may be incidentally detected during testicular tumor staging.
Report Sentence
A well-defined, mildly enhancing soft tissue density mass measuring approximately ___ cm in the right/left scrotal paratesticular region is seen on CT; no lymphadenopathy.
The most important US finding of adenomatoid tumor is extratesticular location — the tumor is positioned outside the testis, on the epididymis or tunica albuginea. Testicular parenchyma is normal in echogenicity and structure. This finding is critical for distinguishing from intratesticular tumors (seminoma, embryonal carcinoma) because intratesticular solid masses are considered malignant until proven otherwise. The tumor-testis interface is clearly visible and there is no invasion sign.
Report Sentence
The paratesticular solid nodule shows extratesticular location separate from the testicular parenchyma; testicular parenchyma is normal in echogenicity and the tunica albuginea is intact.
Criteria
Composed of epithelioid cells forming tubular or glandular structures. Most common histological variant.
Distinct Features
Homogeneous hypoechoic nodule on US, moderate T2 hyperintensity on MRI. May have cystic spaces.
Criteria
Few epithelioid cells within dense fibrous stroma. More fibrotic and firm.
Distinct Features
Isoechoic to mildly hyperechoic on US. Isointense to mildly hypointense on T2 MRI. May be confused with fibroma.
Criteria
Variant with prominent cystic spaces. Dilated tubular structures. Rare.
Distinct Features
Solid-cystic nodule with microcystic areas on US. Markedly hyperintense on T2 MRI. May be confused with spermatocele.
Distinguishing Feature
Spermatocele anechoic cystic, in epididymal head; adenomatoid solid, in epididymal tail. Posterior acoustic enhancement in spermatocele.
Distinguishing Feature
Epidermoid cyst intratesticular, 'onion ring' appearance; adenomatoid extratesticular, homogeneous solid.
Distinguishing Feature
Leiomyoma markedly hypointense on T2 (smooth muscle), adenomatoid variable T2 signal. Both benign and extratesticular.
Distinguishing Feature
Seminoma INTRAtesticular, hypo-to-hypervascular; adenomatoid EXTRAtesticular, avascular. AFP/beta-hCG variable in seminoma.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
12-monthAdenomatoid tumor is benign in nature with no malignancy potential. Diagnosis can be made by ultrasonography + clinical evaluation. Conservative follow-up is acceptable for lesions showing typical findings on US (extratesticular, solid, avascular, well-defined) — US control at 6-12 month intervals. Excision is performed in diagnostically uncertain cases (atypical US findings, growing lesion). Radical orchiectomy is not needed — organ-sparing excision is sufficient.
Adenomatoid tumor is completely benign with no malignancy risk. The most important clinical issue is differentiating it from intratesticular malignant lesions — if paratesticular location is demonstrated, testis-sparing surgery (tumor enucleation) can be performed, avoiding orchiectomy. US confirmation of paratesticular location is critical for testis preservation. No recurrence has been reported after surgical excision.