Leydig cell tumor is the most common sex cord-stromal tumor of the testis, comprising 1-3% of all testicular tumors. It originates from interstitial Leydig cells and is a hormone-producing tumor — it may produce testosterone, estrogen, or both. On ultrasonography, it typically appears as a small (<2 cm), homogeneous hypoechoic, well-defined mass with marked hypervascularity. Hormonal symptoms (gynecomastia, precocious puberty, feminization) provide clinical clues. The vast majority (90-95%) are benign; malignant variants are rare, characterized by large size, necrosis, and vascular invasion.
Age Range
30-60
Peak Age
40
Gender
Male predominant
Prevalence
Uncommon
Leydig cell tumor is a sex cord-stromal neoplasm originating from Leydig cells in the testicular interstitium. Normal Leydig cells are responsible for testosterone production and function under LH (luteinizing hormone) stimulation. Tumoral Leydig cells demonstrate autonomous hormone production — they may produce testosterone, estrogen (conversion of testosterone to estrogen via aromatase activity), or both. The small, homogeneous, markedly hypervascular appearance on ultrasonography reflects the tumor's rich vascular network required for intense steroidogenesis — steroid synthesis requires high blood flow and oxygen delivery. Reinke crystals (eosinophilic rod-shaped intracytoplasmic inclusions) are a pathognomonic histological finding also found in normal Leydig cells. Malignant transformation is rare and associated with large size (>5 cm), necrosis, high mitotic index, vascular invasion, and DNA aneuploidy.
A small, homogeneous hypoechoic, markedly hypervascular intratesticular mass on ultrasonography combined with hormonal symptoms such as gynecomastia, precocious puberty, or feminization is highly typical for Leydig cell tumor. Normal tumor markers (AFP, beta-HCG) and elevated serum testosterone/estrogen strongly support this diagnosis.
Leydig cell tumor typically appears as a small (<2 cm), homogeneous hypoechoic, well-defined intratesticular mass on ultrasonography. Internal structure is remarkably uniform and may resemble seminoma but is typically smaller. May be mildly hyperechogenic (rare) due to lipid-containing Leydig cells. Margins are smooth and sharp. In large tumors (>5 cm, malignancy suspicion), heterogeneity and necrosis areas may be seen.
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A small, homogeneous hypoechoic, well-defined mass is seen in the testicular parenchyma; Leydig cell tumor should be considered in the context of hormonal symptoms.
Color Doppler ultrasonography demonstrates marked hypervascularity in Leydig cell tumor despite its small size. Intralesional vascular structures show organized distribution and may display radial or peripheral pattern. This disproportionate vascularity reflects the tumor's high vascular support need for steroidogenesis and provides an important clue in distinguishing from other small testicular lesions. As epidermoid cyst and simple cyst are completely avascular, Leydig cell tumor should be primarily considered in a small hypervascular lesion.
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Color Doppler examination demonstrates marked hypervascularity disproportionate to the small mass size, a finding favoring steroid-producing tumor (Leydig cell tumor).
On T2-weighted MRI, Leydig cell tumor shows low-to-intermediate signal intensity distinctly lower than normal testicular parenchyma. Homogeneous signal pattern is seen in small tumors. Unlike seminoma, it is generally smaller and accompanied by hormonal findings. Heterogeneity and necrosis areas may be seen in malignant variants.
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The testicular mass demonstrates low-to-intermediate signal intensity on T2-weighted sequences, distinctly hypointense compared to normal parenchyma.
On T1-weighted MRI, Leydig cell tumor may show isointense or slightly hyperintense signal. Mild T1 hyperintensity may be seen due to lipid content. Prominent and homogeneous enhancement on contrast-enhanced series — reflecting rich vascular structure. Early intense enhancement on dynamic contrast series is characteristic of steroidogenic tumor.
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The mass shows isointense to slightly hyperintense signal on T1-weighted sequences with prominent homogeneous enhancement on contrast-enhanced series.
On DWI, Leydig cell tumor shows mild-to-moderate diffusion restriction. ADC values are generally higher than germ cell tumors (1.0-1.4 × 10⁻³ mm²/s). This finding reflects Leydig cell tumor's lower cellularity and wider cytoplasm. DWI may help in distinguishing from seminoma — seminoma ADC values are generally lower.
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The mass shows mild diffusion restriction on DWI with ADC values higher compared to germ cell tumors.
On CT, Leydig cell tumor appears as a well-defined, homogeneously enhancing small mass. CT is rarely used for primary evaluation of this tumor but is needed for staging when malignant variant is suspected. In malignant Leydig cell tumor, retroperitoneal lymphadenopathy and distant metastases (lung, liver, bone) are investigated. Metastasis is not expected in benign variants.
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A small, well-defined, homogeneously enhancing mass is seen in the testicular parenchyma on contrast-enhanced CT.
Criteria
In 90-95% of cases. <5 cm, no necrosis, low mitotic index, no vascular invasion. Testis-sparing surgery (enucleation) possible.
Distinct Features
Small, homogeneous, well-defined mass on US. Homogeneous signal and enhancement on MRI. Hormonal symptoms regress after surgery.
Criteria
In 5-10% of cases. >5 cm, necrosis areas, high mitotic index (>3/10 HPF), vascular invasion, DNA aneuploidy. High metastasis risk. Radical inguinal orchiectomy + RPLND.
Distinct Features
Large, heterogeneous, irregularly marginated mass with necrosis on US. Heterogeneous signal and enhancement on MRI. Retroperitoneal lymphadenopathy on CT.
Criteria
Rare. Simultaneous or sequential Leydig cell tumor in both testes. May be associated with congenital adrenal hyperplasia or Klinefelter syndrome.
Distinct Features
Bilateral small hypoechoic hypervascular lesions on US. Hormonal evaluation and genetic testing recommended.
Distinguishing Feature
Seminoma is generally larger (3-6 cm), Leydig cell tumor usually small (<2 cm). Both are hypervascular but Leydig tumor is accompanied by gynecomastia/hormonal symptoms. AFP and beta-HCG normal in Leydig.
Distinguishing Feature
Sertoli cell tumor is also a sex cord-stromal tumor but hormonal symptoms are less prominent. May be indistinguishable from Leydig on US. Calcifications more common in Sertoli. Inhibin B may be elevated in Sertoli.
Distinguishing Feature
Epidermoid cyst is completely avascular with 'onion ring' pattern. Leydig cell tumor shows marked hypervascularity. No hormonal symptoms in epidermoid cyst.
Distinguishing Feature
Adenomatoid tumor is usually extratesticular (epididymal origin) with rare intratesticular location. Leydig cell tumor is intratesticular. No hormonal symptoms in adenomatoid tumor.
Urgency
moderateManagement
Benign: testis-sparing surgery (enucleation) with frozen section. Malignant: radical inguinal orchiectomy + RPLND. No effective chemotherapy or radiation for malignant variant. Hormonal evaluation (testosterone, estradiol, LH, FSH) mandatory.Biopsy
Not NeededFollow-up
Hormonal levels post-surgery (should normalize). Benign: annual US surveillance of contralateral testis. Malignant: CT surveillance for retroperitoneal and distant metastases, long-term follow-up as late relapses reported.Leydig cell tumor is predominantly a benign neoplasm treatable with testis-sparing surgery. Frozen section is critical for intraoperative malignancy assessment. Hormonal symptoms (gynecomastia) regress after surgery. Malignant variant is rare and requires aggressive surgery; no effective chemotherapy or radiation available. Normalization of serum testosterone and estrogen levels indicates treatment success.
Leydig cell tumor is mostly benign (90%+) and can be treated with testis-sparing surgery (enucleation). Frozen section pathology is important for intraoperative assessment. Malignancy criteria: >5 cm size, necrosis, vascular invasion, increased mitotic activity, and DNA aneuploidy. Hormonal symptoms (gynecomastia, erectile dysfunction, decreased libido) usually regress after tumor resection. Germ cell tumor markers (AFP, hCG) are normal — this is important in differential diagnosis.