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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

Anterior Mediastinal Masses

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