Yolk sac tumor (endodermal sinus tumor) is the most common testicular germ cell tumor in childhood, while in adults it is typically found as a component of mixed germ cell tumors. Pure form is rare in adults (2-3%). On ultrasonography, it appears as a heterogeneous mass with solid-cystic mixed structure and may show reticular-cavernous pattern. Markedly elevated serum AFP is a pathognomonic finding. Schiller-Duval bodies are histologically characteristic. It shows high sensitivity to chemotherapy and has excellent prognosis in pediatric cases.
Age Range
0-10
Peak Age
3
Gender
Male predominant
Prevalence
Uncommon
Yolk sac tumor is a malignant germ cell tumor showing extra-embryonal yolk sac (vitelline sac) differentiation. In childhood, it develops independently of GCNIS/IGCN, while in adults it arises on a background of GCNIS. Tumor cells create various histological patterns mimicking yolk sac endoderm in embryonal development: reticular, papillary, solid, glandular, hepatoid, and parietal patterns. Schiller-Duval bodies (papillary arrangement of tumor cells around a central vascular structure) are a pathognomonic histological finding resembling glomeruloid structures. AFP production reflects the normal embryonic function of yolk sac endoderm — in the fetal period, the liver and yolk sac are the main producers of AFP. The reticular-cavernous pattern on ultrasonography reflects the tumor's reticular growth pattern within loose myxoid stroma and explains the mosaic distribution of solid and cystic areas.
A solid-cystic mixed intratesticular mass with reticular-cavernous pattern on ultrasonography combined with markedly elevated serum AFP is highly typical for yolk sac tumor. This combination is nearly pathognomonic especially in childhood (<3 years).
Yolk sac tumor appears as a heterogeneous mass with solid-cystic mixed structure on ultrasonography. The characteristic reticular-cavernous pattern results from a 'honeycomb'-like appearance created by tumor cell clusters and small cystic spaces distributed within loose myxoid stroma. Solid areas appear at medium echogenicity, cystic areas anechoic-hypoechoic. The tumor may be well-defined but may show irregular margins at large sizes.
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A heterogeneous mass with solid-cystic mixed structure is seen in the testicular parenchyma with reticular-cavernous pattern consistent with yolk sac tumor; serum AFP level should be checked.
Color Doppler ultrasonography demonstrates intralesional vascularity in the solid components of yolk sac tumor. Vascularity may not be as prominent as embryonal carcinoma but is clearly seen in solid areas. Cystic-myxoid areas are avascular. Spectral Doppler detects arterial flow with low-to-intermediate resistive index. Vascularity distribution may be irregular, consistent with the reticular pattern.
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Color Doppler examination demonstrates intralesional vascularity in solid components of the mass, with avascular appearance of cystic areas.
On T2-weighted MRI, yolk sac tumor demonstrates heterogeneous signal. Cystic-myxoid areas show high T2 signal, solid areas show low-to-intermediate signal. The reticular pattern is also discernible on MRI — alternating arrangement of solid and cystic areas. The tumor usually shows distinctly different signal from normal testicular parenchyma. If necrosis areas are present, additional T2 hyperintense foci are formed.
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The testicular mass demonstrates heterogeneous signal on T2-weighted sequences with high-signal cystic-myxoid areas and low-signal solid areas forming a reticular pattern.
On T1-weighted sequences, yolk sac tumor shows isointense to hypointense signal. Myxoid areas show low T1 signal, solid areas isointense signal. If hemorrhagic areas are present, T1 hyperintense foci may be seen but not as frequently as in choriocarcinoma. On contrast-enhanced series, solid components show enhancement while myxoid-cystic areas do not enhance.
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The mass shows isointense to hypointense signal on T1-weighted sequences with enhancement in solid components on contrast-enhanced series.
On DWI, solid components of yolk sac tumor show diffusion restriction. Cystic-myxoid areas do not show restriction. ADC values are low in solid areas (0.7-1.1 × 10⁻³ mm²/s), high in cystic areas. DWI provides important information in tumor viability assessment and treatment response monitoring.
Report Sentence
Diffusion restriction is seen in solid components of the mass on DWI, with no restriction in cystic-myxoid areas.
On contrast-enhanced CT, yolk sac tumor appears as a mass with heterogeneous enhancement. CT is primarily used for staging and follow-up. Retroperitoneal lymphadenopathy and pulmonary metastases are evaluated. In pediatric cases, CT use is limited due to radiation dose and MRI is preferred. AFP levels and CT findings are evaluated together — if AFP elevation persists, occult residual disease should be investigated.
Report Sentence
The mass demonstrates heterogeneous enhancement on contrast-enhanced CT; retroperitoneal and pulmonary metastases should be investigated for staging purposes.
Criteria
Most common histological pattern. Tumor cells forming reticular network within loose myxoid stroma. Schiller-Duval bodies most commonly seen in this pattern. Honeycomb-like microcystic appearance on ultrasonography.
Distinct Features
Reticular pattern is most prominent in this subtype with alternating arrangement of solid and small cystic areas on ultrasonography. Heterogeneous T2 signal with microcystic structure is characteristic on MRI.
Criteria
Less common. Tumor cells showing diffuse solid growth with minimal cystic component. May show histological similarity to embryonal carcinoma. AFP elevation and CD30 negativity help in differential diagnosis.
Distinct Features
May appear as a more homogeneous hypoechoic mass on ultrasonography, reticular pattern may not be prominent. May be confused with seminoma but AFP elevation is distinguishing. Marked diffusion restriction on DWI.
Criteria
Rare. Composed of hepatocyte-like cell clusters. Very high AFP production characteristic. May be histologically confused with hepatocellular carcinoma metastasis.
Distinct Features
Appears as solid mass on ultrasonography, reticular pattern usually absent. AFP may be at very high levels (>10,000 ng/mL). May show homogeneous enhancement on MRI.
Distinguishing Feature
Seminoma shows homogeneous hypoechoic appearance, while yolk sac tumor shows solid-cystic mixed structure with reticular pattern. AFP is always normal in seminoma; AFP is markedly elevated in yolk sac tumor. Age difference is also important — yolk sac tumor is more common in children, seminoma at age 30-40.
Distinguishing Feature
Embryonal carcinoma appears as a more solid, aggressively marginated heterogeneous mass with prominent hemorrhage. Yolk sac tumor has reticular-cavernous pattern with more prominent cystic component. AFP is at much higher levels in yolk sac tumor. CD30 is positive in embryonal carcinoma, negative in yolk sac tumor.
Distinguishing Feature
Teratoma has predominantly cystic structure with prominent calcifications and fat components. Calcification is rare in yolk sac tumor, reticular myxoid pattern is dominant. AFP is normal in pure teratoma; markedly elevated in yolk sac tumor.
Distinguishing Feature
Simple testicular cyst is an anechoic, thin-walled, well-defined lesion with posterior acoustic enhancement and is avascular. Yolk sac tumor has mixed structure with solid components showing vascularity. AFP is normal in simple cyst.
Urgency
highManagement
Radical inguinal orchiectomy. Pediatric cases: surgery often curative for stage I. Adult cases: BEP chemotherapy for advanced stages. AFP monitoring critical for treatment response and recurrence detection.Biopsy
Not NeededFollow-up
Serum AFP monitoring every 1-2 months for first 2 years. CT surveillance for retroperitoneal and pulmonary metastases. AFP normalization half-life (5-7 days) used to assess treatment response — slower decline suggests residual disease.Yolk sac tumor is a tumor with high sensitivity to chemotherapy. In pediatric cases, surgery alone may be sufficient for stage I with excellent prognosis. In adult cases, it is more commonly seen as a component of mixed germ cell tumors and treated with BEP chemotherapy. AFP monitoring is critically important in treatment response and recurrence detection — AFP half-life (5-7 days) determines the expected decline rate, and slower than expected decline may indicate residual disease.
Yolk sac tumor is the most common testicular malignancy in children with excellent prognosis when diagnosed early. In children with stage I disease, cure rates exceed 90% after radical inguinal orchiectomy. AFP levels are the most important marker for monitoring treatment response and recurrence. In adults, it is usually found as a component of mixed germ cell tumor, and treatment follows NSGCT protocols. Retroperitoneal lymph node dissection is avoided if possible in pediatric cases.