Mediastinal Teratoma
Dermoid

• 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 teratomas
• 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
• Symptoms
  • 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
• 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

Enhanced CT scan of the chest shows large, septated anterior
mediastinal mass containing fat and bony elements

• 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