Teratoma of the mediastinum

Definition

A germ cell tumour showing differentiation into at least two germinal layers (ectoderm, mesoderm or endoderm).

Mature teratoma: composed solely of mature adult-type tissues.
- Dermoid: a cystic mature teratoma lined by keratinising squamous epithelium with skin appendages.
Immature teratoma: contains immature/embryonal/fetal tissues, with or without mature tissues.
Teratoma with somatic-type malignancy: incudes a non-germ cell malignant component, which may be carcinoma or sarcoma.
Teratomatous component in a mixed germ cell tumour.

Epidemiology

Immature teratoma occurs almost only in males. Mature teratoma may be associated with Klinefelter's syndrome.

Clinical features

An endocrine component may cause hyperinsulinaemia and hypoglycaemia.

Radiology and macroscopic appearances

Mature teratomas are usually multicystic and may calcify.

Histopathology

Mature teratoma: contain skin and skin appendages, plus pancreatic, bronchial, neural, gastrointestinal, smooth muscle and adipose tissues. Less often, there is skeletal muscle, bone, cartilage, salivary gland, prostate or liver.
Immature teratoma: the immature components consist of neuroepithelium, immature glands, fetal lung, immature cartilage, immature bone, rhabdomyoblasts and blastema-like stroma.

Immunohistochemistry

	Desmin	positive in rhabdomyoblasts
	Myogenin	positive in rhabdomyoblasts
	S-100	positive in neural tissue
	NSE	positive in neural tissue
	AFP	positive in liver and immature neuroepithelium
	S-100	positive in immature cartilage
	GFAP	positive in immature cartilage
	PLAP	negative in pure teratoma
	hCG	negative in pure teratoma
	CD30	negative in pure teratoma

Positivity for S-100, HMB45, Melan-A and CD99 has been reported in a teratocarcinoma metastatic to bone marrow and interpreted as evidence of neuroectodermal/melanomatous differentiation1.

Differential diagnosis

Mixed germ cell tumour with a teratomatous component.

Prognosis

Mature teratoma is benign at any age.
Immature teratoma shows a prognosis which is age-dependent. It has a very good prognosis in children if there is no malignant component and an 80% three-year survival if there is a malignant component. In adults, the prognosis is less certain: a malignant component may only manifest in metastases.

References

0 Tumours of the Lung, Pleura, Thymus and Heart. WHO Classification of Tumours. IARC Press 2004.

1 Orduz R, Sabattini E, Bacci F, et al. Pitfalls in diagnosis: primary mediastinal non-seminomatous germ cell tumour with bone marrow metastasis showing melanoma-like phenotype. Histopathology 2005; 47:645-6

This page last revised 1.3.2006.