MATURE CYSTIC TERATOMA ARISING IN THE ANTERIOR MEDIASTINUM
Approximately 20% of primary mediastinal neoplasms are of germ-cell origin. Of these, roughly 80% are of teratomatous origin. Mediastinal teratomas are five times more common in adults than in children. How exactly these lesions originate remains an area of speculation and debate. Cytogenetic studies, however, have confirmed an association with Klinefelter's Disease. The most commonly associated chromosomal abnormality associated with mediastinal teratomas is an isochromosome on the short arm of chromosome 12[i(12p)].
Mature cystic teratomas account for 95% of all primary mediastinal teratomas, whereas immature teratomas only account for roughly 1%. Mature cystic teratomas are large, benign lesions composed of one or more of the embryonic germ layers (ectoderm, mesoderm, and endoderm). When they are composed primarily of mature ectoderm, they are often referred to as "dermoids." In order to be classified as benign, the lesion can show no trace of immature mesenchymal elements.
As far as gross and histologic features are concerned, mature cystic teratomas are identical to their gonadal counterparts. Typically these lesions present as large, polypoid masses with focal intimal calcification. Residual thymus is also often adhered to the capsular surface or wall of these lesions. Sectioning usually demonstrates fleshy, cystic areas with abundant sebaceous material and hair. Mature ectoderm is the most common of the three germ layers present, although bone, cartilage, respiratory epithelium and neural tissues may also be seen.
Patients usually present with symptoms produced by compression and/or invasion of important structures found within the mediastinum. The most common complaints are cough, dyspnea, and chest pain. Occasionally, the tumor may invade the adjacent pulmonary parenchyma and result in the expectoration of hair (trichoptysis). Additional complications, although infrequent, include pneumothorax, lipoid pneumonia, and destruction of nervous system structures.
Although x-ray and computer aided tomography studies can help to aid in a diagnosis, they can only confirm a diagnosis when they demonstrate the presence of teeth or other organized skeletal parts. Mediastinal cystic hygromas, cysts of foregut origin, alimentary canal duplication and a variety of benign and malignant lesions all must be considered in the differential diagnosis until proven otherwise (usually by biopsy or surgical removal).
The prognosis of patients undergoing surgery in which the entire lesion is removed is excellent. Barring complications, surgery is a completely curative measure for patients with mature cystic teratomas.
Contributed by Jason C. Fowler, BS and Uma NM Rao, MD