Mixed germ cell tumors of the mediastinum or mediastinal mixed germ cell tumors are malignant non-seminomatous germ cell tumors of the mediastinum consisting of more than one type of germ cell tumor.
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Terminology
The term ‘malignant teratoma’ is not recommended.
Epidemiology
Mixed germ cell tumors of the mediastinum are rare and are almost always seen in men 1. In adults, the two most common tumor elements are teratoma and embryonal carcinoma, whereas in children yolk sac and teratomatous components are more commonly seen 1.
Risk factors
Diagnosis
The final diagnosis is based on histology and requires the presence of more than one type of germ cell tumor 1.
Clinical presentation
Clinical signs and symptoms include chest-related symptoms such as dyspnea, chest pain, cough, and superior vena cava syndrome like in other mediastinal germ cell tumors. Similarly, there will be an elevation of serum tumor markers 1,2.
Complications
Mediastinal choriocarcinomas might cause the following complications ref:
- superior vena cava obstruction
- infiltration of adjacent structures
- nodal and distant metastases to lung, pleura, liver bones and brain
Pathology
Mixed germ cell tumors are characterized by different types of germ cell tumors e.g. seminomatous and teratomatous components 1.
Pathogenesis
Mixed germ cell tumors in adults frequently feature chromosomal amplifications or isochromosome 12p.
Children lack the 12p gains but often have additions in the 1q, 3 and 20q locations as well as losses at 1p, 4q and 6q. Patients with Klinefelter syndrome have additional copies of the X-chromosome 1.
Location
Primary mediastinal mixed germ cell tumors are usually found in the anterior mediastinum 1.
Macroscopic appearance
Mixed germ cell tumors are heterogeneous with a solid fleshy gross appearance with intermingled areas of hemorrhage and necrosis and variably cystic or fatty components 1.
Microscopic appearance
Microscopically mediastinal mixed germ cell tumors are characterized by the different morphologies of pure germ cells in any combination 1.
Radiographic features
On imaging studies mixed germ cell tumors are heterogeneous masses with areas of hemorrhage and necrosis.
Cystic spaces and adipose tissue indicate teratomatous components.
Plain radiograph
Chest x-rays might show widening of the anterior mediastinum 2,3.
CT
Mixed germ cell tumors have a heterogeneous appearance with signs of hemorrhage and necrosis as well as variably cystic and/or fatty components 2-4. CT might reveal infiltration of adjacent structures, including superior vena cava compression, pleural or pericardial effusions, and distant metastases 3.
MRI
MRI reports of mixed germ cell tumors are scarce. They have been described as large heterogeneous masses 4.
MRI can assess fatty and cystic components 4.
Radiology report
The radiological report should include a description of the following:
- location and extent of the tumor
- relation to the heart and great vessels
- infiltration and/or compression of adjacent structures
- superior vena cava obstruction
- pleural effusion
- pericardial effusion
- nodal disease
- distant metastases
Treatment and prognosis
Management includes chemotherapy with subsequent surgical resection. Prognosis is not good with a 5-year overall survival of about 45% 1. Patients younger than 30 years and children have a better prognosis. Localized disease and normal hCG levels are also favorable 1.
Differential diagnosis
Condition or tumors that might mimic the appearance of tumors include 1:
- lymphoma
- thymoma
- thymic carcinoma
- pure mediastinal germ cell tumors
- metastatic carcinoma
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