John D. Hainsworth, MD; F. Anthony Greco, MD
The biology and clinical characteristics of mediastinal germ cell tumors have been defined during the last 30 years. These neoplasms, although rare, are of particular interest because they predominantly affect young males and because curative therapy is now available for many patients. The clinical and pathologic characteristics of benign and malignant germ cell tumors and of "poorly differentiated carcinoma" of the mediastinum are presented, with special attention focused on the treatment of these neoplasms.
Benign Teratomas of the Mediastinum
Benign teratomas of the mediastinum (mature cystic teratomas or "dermoid" tumors) are rare and account for only 3 to 12% of mediastinal tumors. Although these tumors have been described in patients with ages ranging from 7 months to 65 years, most occur in young adults, with an approximately equal incidence in males and females. No predisposing conditions or associated abnormalities have been recognized in patients developing these tumors.
Benign mediastinal teratomas have a histologic appearance identical to that of benign teratomas arising in the more common ovarian location. These tumors are usually well encapsulated and are composed either of a single large cystic cavity or of several smaller intercommunicating cystic spaces. On histologic examination, mature tissue from ectodermal, mesodermal, and endodermal germ cell layers is typically present. Mature tissue that recapitulates the histology of any human organ can be found in these tumors. However, the ectodermal component (ie, skin, sebaceous tissue, neural tissue) is usually predominant.
Approximately 95% of benign teratomas arise in the anterior mediastinum; the remainder arise in the posterior mediastinum. These tumors are slow growing and in recent years, 50 to 60% of patients have been asymptomatic at the time of diagnosis by routine chest radiography. When symptoms are present, dyspnea and substernal chest pain are the most common. Cough productive of hair or sebum is pathognomonic of a benign mediastinal tumor. However, this distinctive symptom is extremely rare and occurs late in the natural history of this condition following tumor rupture into the tracheobronchial tree. Superior vena caval syndrome is also rare and is a late manifestation. Most patients with benign mediastinal teratomas appear healthy, and physical examination contributes little to the diagnosis. Likewise, laboratory evaluation is usually normal. Serum levels of human chorionic gonadotropin (HCG) and α-fetoprotein are always normal in patients with benign teratoma.
The chest radiograph typically reveals a well-circumscribed anterior mediastinal mass that often protrudes into one of the lung fields. These tumors are usually large at the time of diagnosis; in a recent series, the median size was 10 X 8.5 X 5.4 cm. Occasionally, chest radiography identifies teeth within the tumor, a pathognomonic finding. Calcification is present in up to 25% of tumors, occurring in fragments of bone, in the tumor wall, or in other areas throughout the tumor, in addition to its occasional occurrence in teeth.
Surgical excision is the treatment of choice for benign teratoma of the mediastinum. Median sternotomy is usually the best surgical approach, although successful resection can also be accomplished by thoracotomy. Surgical removal is sometimes difficult because of the large size of the tumor and the involvement of other structures: pericardium, lung, great vessels, thymus, chest wall, hilar structures, and diaphragm, in decreasing order of frequency. Some 10 to 15% of patients require additional procedures (eg, lobectomy, pericardiectomy) for complete tumor resection. Benign teratomas are resistant to radiation and cytotoxic drugs, and these modalities have no role in their treatment.
Tumor recurrence is rare following complete surgical resection. Prolonged survival has also been reported in patients who underwent only subtotal resection owing to the involvement of vital mediastinal structures. The operative mortality rate in recent years has been very low.