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Primary mediastinal teratomas account for approximately 8% to 20% of anterior mediastinal neoplasms and up to 80% of mediastinal germ cell tumors. Although mediastinal germ cell tumors account for only 3% to 5% of all germ cell tumors, they are the most common extragonadal site for a primary germ cell tumor.
Mediastinal germ cell tumors are caused by malignant change in a primordial germ cell. Like their gonadal counterparts, mediastinal teratomas are composed of tissues representing one or more of the embryonic germ cell layers foreign to the organ or anatomic site in which they occur. The tumor may attempt organ formation and can contain teeth, skin, and hair (ectodermal derivatives); cartilage and bone (mesodermal derivatives); or bronchial, intestinal, and pancreatic tissue (endodermal derivatives).
Mature teratomas represent approximately 60% to 70% of mediastinal germ cell tumors and are well differentiated and benign.
Those composed exclusively of mature ectoderm are often termed “dermoids.” The presence of any fetal or immature neuroectodermal or mesenchymal elements characterizes a teratoma as immature, which has a good prognosis but a greater likelihood of recurrence or metastasis. Rarely, a mature teratoma can contain a focus of carcinoma, sarcoma, or malignant germ cell tumor; one that does is termed a “malignant teratoma” or “teratocarcinoma.”
Most mature mediastinal teratomas occur in children and young adults, with the average age at presentation approximately 20 years.
Unlike malignant germ cell tumors, which occur nearly exclusively in men, teratomas occur with equal frequency in men and women. Although the asymptomatic lesion is more likely benign, the lack of symptoms does not ensure a benign process. Similarly, a symptomatic lesion is more likely malignant, but benign lesions also may be symptomatic. In infants and children, the relatively smaller mediastinal dimensions and the predominance of malignant lesions make most mediastinal masses symptomatic. Mature teratomas can be asymptomatic in up to 50% of patients, particularly in children and young adults.
Older individuals more typically present with signs and symptoms related to intrathoracic compression from the local growth of the mass, with chest pain, cough, and dyspnea as the most common complaints. Constitutional symptoms such as fever, weight loss, and endocrine dysfunction have also been described. Digestive enzymes secreted by intestinal mucosa or pancreatic tissue in the tumor can precipitate rupture into the bronchi, pleura, pericardium, or lung. Expectoration of hair (trychoptysis) or sebum is a rare but pathognomonic event, indicating that the tumor has ruptured into a bronchus.
Radiographic and Laboratory Features
Most teratomas arise in the anterior-superior mediastinum. Radiologically, teratomas are rounded to lobulated, well-defined anterior mediastinal masses located in front of the roots of the aorta and main pulmonary artery. The bulk of the mass may protrude to one side of the midline and can reach a large size. On computed tomography (CT) scan, teratomas usually appear as multilocular cystic tumors with walls of variable thickness (Fig I). A combination of fluid, soft tissue, calcium, or fat attenuation in an anterior mediastinal mass is a highly specific finding that allows for a reliable diagnosis of mature teratoma.
Fat-fluid levels produced by the high lipid content in the cystic spaces are also specific for teratoma. The presence of calcification in 20% to 40% of these tumors suggests the diagnosis of benign teratoma. Organized bone or teeth may occasionally be identified. Rarely, the tumor ruptures into the pericardium or the pleura, in which case a fat-fluid level may also be present. Magnetic resonance imaging (MRI) has not been shown to provide any significant advantage over CT scans.
Benign teratomas by definition lack alpha-feto-protein (AFP) and beta-human choriogonadotrophins (b-HCG). Elevated serum AFP or b-HCG level indicates a malignant component to the teratoma, such as embryonal carcinoma, endodermal sinus tumor, or choriocarcinoma.
Therapy and Clinical Outcome
Although mature teratoma is a benign tumor, excessive enlargement may lead to compression and displacement of neighboring thoracic organs. Complete excision, usually performed through a median sternotomy, results in cure.
However, resection may be difficult because of the tumor's large size and adherence to adjacent and vital intrathoracic structures. Occasionally a mature teratoma induces life-threatening complications by virtue of a mass effect on these vital structures. Radiation and chemotherapy have no role in the treatment of benign teratomas.
In immature teratomas, patient age, not histology, appears to be the most significant prognostic factor. This contrasts with ovarian and, to a lesser degree, saccrococcygeal teratomas, in which immature histology denotes malignancy. In the mediastinum, immature teratomas arising in patients younger than age 15 years behave as mass lesions or mature teratomas. Total resection allows long-term survival. In individuals over age 15 years, immature teratomas act as highly malignant neoplasms that can metastasize widely. When an immature teratoma is combined with a malignant germ cell tumor, growth is usually very aggressive, and surgery plays a secondary role in treatment.
Although most patients undergo surgical procedures safely, a subset of patients—particularly children with large anterosuperior or middle mediastinal masses—have an increased risk of severe cardiorespiratory complications during general anesthesia. Exacerbation of superior vena caval obstruction or extrinsic airway compression can occur during general anesthesia because of the loss of negative intrathoracic pressure during respiration, bronchial smooth muscle relaxation that increases bronchial compressibility, and reduced tidal volumes in ventilation. A reduction in tracheal cross-sectional area of more than 35% by CT scan indicates an increased risk with general anesthesia; similarly, reduced pulmonary flow mechanics are a sensitive indicator of functional airway compression and susceptibility to intraoperative airway compromise.
In patients with large mediastinal masses who have an increased anesthetic risk, recommendations for anesthetic management include (1) fiberoptic evaluation of the tracheobronchial tree for evidence of severe extrinsic compression; (2) induction of anesthesia in a semierect position, with the option of changing to the lateral or prone position; (3) use of long endotracheal tubes to advance beyond the site of obstruction; (4) standby rigid bronchoscopy to reestablish an adequate airway; (5) avoidance of muscle relaxants and use of spontaneous ventilation whenever possible; (6) lower extremity intravenous cannulation to provide access to the systemic venous circulation if a sudden superior vena caval obstruction should occur; and (7) standby cardiopulmonary bypass with bilateral groin preparation.