Seminoma is the most common germ cell tumor of the testis, accounting for approximately 40-50% of all testicular malignancies. It typically presents in men aged 30-40 years. On ultrasonography, it characteristically appears as a homogeneous, hypoechoic, well-defined mass with marked hypervascularity. Seminomas are highly sensitive to radiation therapy and chemotherapy, carrying an excellent prognosis. Cryptorchidism is the most significant risk factor, with increased risk also present in the contralateral testis.
Age Range
25-45
Peak Age
35
Gender
Male predominant
Prevalence
Common
Seminoma is a malignant neoplasm originating from primordial germ cells. The tumor cells arise from malignant transformation of totipotent germ cells that migrate to the gonadal ridge during embryonic development. Intratubular germ cell neoplasia (IGCN/GCNIS) is the precursor lesion of seminoma, with tumor cells proliferating within seminiferous tubules and infiltrating the testicular parenchyma. The homogeneous hypoechoic appearance on ultrasonography reflects the tumor's uniform cellular architecture — large cells with glycogen-rich cytoplasm arranged in uniform sheets with minimal stromal component. Hypervascularity reflects the tumor's intense angiogenesis and active metabolic state; prominent intralesional vascular flow on Doppler ultrasonography is the direct imaging correlate of this neoangiogenesis.
The combination of a homogeneous hypoechoic, well-defined testicular mass on ultrasonography with marked hypervascularity on Doppler is highly typical for seminoma. This combination is the most important finding in distinguishing from the heterogeneous structure of non-seminomatous tumors and the avascular nature of epidermoid cysts.
Seminoma appears as a homogeneously hypoechoic mass compared to the testicular parenchyma on ultrasonography. The mass is generally well-defined and may have lobulated contours. Its internal structure is remarkably uniform, with heterogeneity being rare and seen only in large tumors with areas of necrosis or hemorrhage. Homogeneity is the most important distinguishing feature of seminoma and differs from the heterogeneous appearance of non-seminomatous germ cell tumors.
Report Sentence
A homogeneously hypoechoic, well-defined mass is seen within the testicular parenchyma, consistent with seminoma.
Color Doppler ultrasonography demonstrates marked hypervascularity in seminoma. Intralesional vascular structures show organized distribution, typically displaying a striatal or radial pattern. Spectral Doppler reveals arterial flow with low resistive index. This hypervascularity reflects the active angiogenesis of seminoma and is critically important in distinguishing it from avascular lesions such as epidermoid cysts.
Report Sentence
Color Doppler examination demonstrates marked hypervascularity of the mass with organized intralesional vascular pattern.
On T2-weighted MRI sequences, seminoma demonstrates homogeneous low-to-intermediate signal intensity compared to normal testicular parenchyma. While normal testis shows bright signal on T2, seminoma is distinctly lower in signal. This homogeneous signal reduction reflects the tumor's dense cellular architecture and decreased free water content. Fibrous septa may be seen as thin linear T2 hypointense areas within the tumor.
Report Sentence
The testicular mass demonstrates homogeneous low-to-intermediate signal intensity on T2-weighted sequences, consistent with seminoma.
On T1-weighted MRI sequences, seminoma shows isointense to slightly hypointense signal compared to normal testicular parenchyma. Focal T1 hyperintense foci may be seen if areas of hemorrhage are present. On contrast-enhanced T1 sequences, the tumor demonstrates homogeneous and prominent enhancement, reflecting the tumor's rich vascular structure. The enhancement pattern is more homogeneous compared to the irregular enhancement of non-seminomatous tumors.
Report Sentence
The mass shows isointense signal on T1-weighted sequences with homogeneous prominent enhancement on contrast-enhanced series.
Diffusion-weighted imaging (DWI) demonstrates marked diffusion restriction in seminoma. Bright signal is seen at high b-values (b=800-1000) with low ADC values on the ADC map. ADC values typically range from 0.6-1.0 × 10⁻³ mm²/s. These findings reflect the tumor's high cellularity. Diffusion restriction shows homogeneous distribution in seminoma, differing from the heterogeneous diffusion pattern of non-seminomatous tumors.
Report Sentence
The mass demonstrates marked diffusion restriction on diffusion-weighted sequences with low ADC values on the ADC map.
On contrast-enhanced CT, seminoma appears as a homogeneously enhancing testicular mass. Although CT is not the primary modality for testicular evaluation, it is frequently used for staging purposes. Retroperitoneal lymphadenopathy (para-aortic, interaortocaval, precaval nodes) may be detected. While there is no retroperitoneal involvement in stage I, retroperitoneal masses and distant metastases (pulmonary, mediastinal) can be evaluated in advanced stages. Retroperitoneal masses in seminoma typically show homogeneous enhancement.
Report Sentence
The testicular mass demonstrates homogeneous enhancement on contrast-enhanced CT; evaluation for retroperitoneal lymphadenopathy is recommended.
In a subset of seminoma cases, ipsilateral or bilateral testicular microlithiasis may be associated. Microlithiasis appears as multiple 1-3 mm echogenic foci within the testicular parenchyma without acoustic shadowing on ultrasonography. While microlithiasis alone is not specific, its association with seminoma and other germ cell tumors has been demonstrated. In the presence of clinical risk factors (cryptorchidism, contralateral tumor history), microlithiasis warrants follow-up.
Report Sentence
Associated microlithiasis foci are noted within the testicular parenchyma; clinical correlation for germ cell tumor association is recommended.
Non-contrast and contrast-enhanced CT plays a critical role in evaluating retroperitoneal lymph nodes for seminoma staging. Para-aortic and interaortocaval lymph nodes are the primary metastatic sites of seminoma. Left para-aortic and pre-aortic nodes are first affected in left testicular tumors, while interaortocaval and precaval nodes are first involved in right testicular tumors. Retroperitoneal lymph nodes with short-axis diameter >10 mm are considered pathological. In advanced stages, mediastinal lymphadenopathy and pulmonary metastases are evaluated.
Report Sentence
Retroperitoneal para-aortic and interaortocaval lymph nodes should be evaluated for size and morphology on staging CT.
Criteria
Most common type, >95% of all seminomas. Histologically large, round cells with glycogen-rich cytoplasm, lobular pattern divided by fibrous septa, lymphocytic infiltrate. PLAP, OCT3/4, c-KIT positive. AFP always negative.
Distinct Features
Homogeneous hypoechoic mass on ultrasonography, may have lobulated contour due to fibrous septa. Homogeneous low T2 signal on MRI, homogeneous restriction on DWI. Tumor size generally 3-6 cm, tunica albuginea well preserved.
Criteria
Rare type, usually >50 years. Does not originate from GCNIS/IGCN, separate entity. Three cell populations (small, medium, giant). c-KIT and PLAP negative. Very low metastasis risk, excellent prognosis. Not associated with GCNIS.
Distinct Features
May appear more heterogeneous than classic seminoma on ultrasonography, may contain cystic-myxoid areas. Usually diagnosed at larger size (5-15 cm). Bilateral involvement is extremely rare. Older age group is an important clinical clue suggesting this subtype.
Criteria
10-15% of seminomas contain syncytiotrophoblastic giant cells producing beta-HCG. Mild-to-moderate serum beta-HCG elevation (<200 IU/L). AFP always normal. Prognosis similar to classic seminoma, treatment approach unchanged.
Distinct Features
May be indistinguishable from classic seminoma on imaging. In rare cases, intratumoral hemorrhage foci may be present, causing mild heterogeneity on ultrasonography. Clinically, gynecomastia or beta-HCG elevation may provide clues.
Distinguishing Feature
Non-seminomatous GCT shows heterogeneous echotexture, cystic areas, calcifications, and irregular margins on ultrasonography, while seminoma has homogeneous hypoechoic appearance. AFP elevation is expected in non-seminomatous tumors.
Distinguishing Feature
Lymphoma typically occurs in men >60 years and may be bilateral. On ultrasonography, it may show diffuse infiltrative pattern preserving normal testicular shape. Seminoma forms a focal mass and occurs in the 30-40 age group. LDH elevation is more pronounced in lymphoma.
Distinguishing Feature
Epidermoid cyst is characterized by 'onion ring' or 'target' pattern and is completely avascular on Doppler. Seminoma demonstrates marked hypervascularity. In epidermoid cyst, serum tumor markers are normal and it does not show diffusion restriction on MRI.
Distinguishing Feature
Leydig cell tumor is generally small (<2 cm), hypoechoic and hypervascular but may be accompanied by gynecomastia and hormonal symptoms. Seminoma is usually larger and does not show hormonal symptoms. Serum testosterone and estrogen levels may be elevated in Leydig cell tumor.
Distinguishing Feature
Orchitis is characterized by diffuse testicular enlargement and heterogeneous hypoechoic appearance. Clinically, pain, fever, and scrotal erythema are present. Epididymal involvement is common. Seminoma presents as a painless mass and is usually a localized focal lesion. On Doppler, orchitis shows diffuse hypervascularity while seminoma shows focal hypervascularity.
Urgency
highManagement
Radical inguinal orchiectomy followed by staging CT. Treatment depends on stage: surveillance, radiation therapy, or chemotherapy (BEP regimen). Seminoma is highly curable with >95% overall survival rate.Biopsy
Not NeededFollow-up
Regular surveillance with CT, tumor markers (beta-HCG, LDH), and physical examination. Stage I: surveillance preferred with CT every 3-6 months for 2 years, then annually. Advanced stages: post-chemotherapy CT assessment.Seminoma is a tumor with a high cure rate. Radical inguinal orchiectomy is the standard first-line treatment — transscrotal biopsy is contraindicated. In stage I, options include surveillance, radiation therapy, or single-dose carboplatin. In advanced stages, BEP chemotherapy (bleomycin, etoposide, cisplatin) is highly effective. AFP elevation is not expected in seminoma; if AFP is elevated, a non-seminomatous component should be investigated. Overall survival rate exceeds 95%.
Seminoma is the most common type of testicular germ cell tumor with an excellent prognosis. In stage I disease, cure rates exceed 99% after radical inguinal orchiectomy. The tumor is radiosensitive and chemosensitive. Staging is performed with CT (chest, abdomen, pelvis). AFP elevation is not expected in seminoma — if elevated, mixed germ cell tumor should be considered and treatment planned accordingly.