Mediastinal Teratoma

General Considerations

• Mediastinum is a rare site for occurrence of teratomas, most being ovarian in origin

• Arise from primitive germ cell rests

• Supposed to migrate along urogenital ridge to primitive gonad

• Journey is interrupted in the mediastinum

• May be solid or cystic

• Most are cystic

• Three major categories

• Mature teratomas

• Well-delineated from surrounding tissues

• Contain ectodermal elements along with cartilage, fat and smooth muscle

• Immature teratomas

• Same elements as above with primitive tissues found in fetus

• Teratomas with malignant transformation

• Overall about 30% are malignant

• Usually adenocarcinoma in mature teratomas

• Angiosarcoma or rhabdomyosarcoma in immature teratoma

• Most of the cystic lesions are benign and most of the solid lesions are malignant

• Both occur early in life—young adults most commonly

• DDX from thymomas which usually occur in 5th or 6th decade

Clinical Findings

• Usually asymptomatic

• Large lesions can cause shortness of breath, cough or retrosternal pain or fullness

• Rare rupture of dermoid into trachea which leads to trichoptysis—expectoration of hair

Differential Diagnosis

Associations

• Non-lymphocytic leukemia and malignant histiocytosis with immature teratomas

Imaging findings

• Most occur in the anterior mediastinum, near junction of great vessels and heart

• Benign lesions are usually smooth in contour whereas malignant masses tend to be lobulated

• Usually larger than thymomas

• Calcification may rarely occur but is of no help since thymomas also calcify

• Exception would be the very rare occurrence of a tooth or bone in a dermoid

• CT shows fatty mass with globular calcifications and rarely a tooth or bone

• Fat-fluid level may be seen on CT

• Rapid increase in size may mean hemorrhage into a cyst rather than enlarging malignancy

Treatment and prognosis

• Mature teratomas

• For benign cystic teratomas, surgical resection

• Excellent prognosis

• Immature teratomas

• In childhood, surgical excision is often successful

• In adults, tend to have a more malignant course

• Teratomas with malignancy

• Usually highly aggressive

• Poor prognosis

• Teratoma versus dermoid

• Dermoid contain only epidermis

• Teratomas contain all 3 germ layers, but are mostly endodermal when malignant

Other germ cell neoplasms

• Benign dermoid cysts

• Benign and malignant teratomas

• Seminomas

• Choriocarcinomas

• Embryonal cell carcinomas

Mediastinal seminomas

• Rare

• Almost always in young men

• Identical to testicular seminoma and ovarian dysgerminoma

• May be well-encapsulated or invasive

• Tends to be lobulated

• Cannot be differentiated from teratoma

Primary choriocarcinoma

• Even rarer than seminoma in the mediastinum

• Only 23 reported in the literature, almost all in men

• Occur between 20-30 years

• May be lobulated

• May have elevated beta sub unit of HCG

• Growth is very rapid leading to dyspnea, hemoptysis, stridor

• Gynecomastia and a + Aschheim-Zondek test can occur

• Rapidly fatal

Mediastinal Teratoma. Contrast-enhanced axial CT scan of the chest demonstrates an anterior mediastinal mass containing calcification (black arrow), fat (white arrow) and soft tissue components (dotted white arrow).
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Fraser and Pare