Mediastinal Germ Cell Tumours

The mediastinum is an uncommon but potential site of germ cell tumour development.


About 3% of germ cell tumours occur in the mediastinum and are the third most common tumour in the mediastinum after thymoma and lymphoma in adults. The differences in incidence based on race seen for testicular germ cell tumours do not exist for mediastinal tumours. Nearly all tumours occur in men; in children teratomas are split evenly whereas yolk sac tumours are more common in girls. The most common variants in adults are:

  • Seminoma
  • Mature teratoma

Aetiology and Pathogenesis

The aetiology of germ cell tumours in the mediastinum is not known. It is postulated that primordial germ cells which develop along the entire axis of the embryo may not complete involute, allowing malignancy to develop. Kleinfelter's syndrome (47 XXY) is associated with mediastinal non-seminomatous germ cell tumours, increasing the risk by at least 50 times. There is not increased incidence in testicular germ cell tumours in these patients.

Natural History

Most mature teratomas are asymptomatic (60%); other tumour types usually produce symptoms due to local effects (eg. pain, dyspnoea). Occasionally excessive production of b-hCG can cause hormonal effects such as hyperthyroidism and gynaecomastia.

Clinical Features

Tumour Features