Description
Yolk Sac Tumours (YSTs), also known as endodermal sinus tumours, represent the most common type of testicular germ cell tumours in children but are rather uncommon in adults. They are characterised by the presence of Schiller-Duval bodies and often secrete alpha-fetoprotein (AFP), which can be a useful marker for diagnosis and monitoring.
Pathogenesis
The pathogenesis of YSTs remains largely unknown. However, the tumour is thought to arise from malignant transformation of germ cells, specifically primitive yolk sac cells.
Epidemiology, Risk Factors & Associations
- YSTs are most commonly diagnosed in infants and young children (less than 3 years old) and represent around 20% of prepubertal testicular tumours.
- Represent 70-80% of testicular tumours in paediatrics.
- In adults, YSTs are usually encountered as a component of mixed germ cell tumours (comprising around 60% of such mixed tumours) rather than as a pure form.
- An association with cryptorchidism (undescended testes) has been suggested, with around 10% of patients having a history of this condition.
Clinical Features
- YSTs often present as a painless, rapidly growing testicular mass.
- Systemic symptoms such as weight loss, fatigue, and lethargy may occur due to the aggressive nature of the tumour.
- Abnormal elevation of serum AFP is frequently seen (up to 90% of cases), and this may be used as a marker for disease progression and response to therapy.
Complications
- If not treated promptly, YSTs can metastasise rapidly, commonly to the lungs, liver, bones and brain.
- Long-term survivors may have a higher risk of secondary malignancies, which may be a late complication of the aggressive chemotherapy regimens used in treatment.
Pathological Features
Histopathology
The characteristic feature of YSTs is the presence of Schiller-Duval bodies, which resemble a central blood vessel surrounded by germ cells, enclosed within a space lined by flat cells.
Serology
YSTs usually cause an increase in serum levels of AFP, which can be used as a marker for diagnosis and to monitor response to treatment.
Radiological Features
US
- Typically shows a heterogeneous mass with hypoechoic or mixed echogenicity. There may also be calcifications.
CT
- May show a heterogeneous, often necrotic mass. Metastatic lesions may also be visible.
MRI
- Generally, YSTs appear hypointense on T1-weighted images and hyperintense on T2-weighted images.
Differential Diagnosis
- Seminoma: Characterised by a homogeneous mass on imaging, normal AFP, and the presence of large cells with clear cytoplasm in histopathology.
- Embryonal carcinoma: May have increased AFP, but typically also has increased hCG, and the histopathology shows epithelial cells with glandular/alveolar patterns.
- Mature teratoma: Shows different types of tissue on histopathology and imaging, and normal AFP.
Management
- The first line of treatment for a localised YST is radical inguinal orchiectomy.
- Given the aggressive nature of YSTs, systemic chemotherapy is often used even in early stages.
- Close monitoring of serum AFP levels is crucial for assessing response to therapy and detecting recurrence.
- Regular surveillance imaging is necessary given the high risk of metastatic disease.