Mediastinal choriocarcinomas or choriocarcinomas of the mediastinum are malignant non-seminomatous germ cell tumors of the mediastinum consisting of trophoblastic cells.
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Epidemiology
Pure choriocarcinomas are rare and account for up to 3% of primary mediastinal germ cell tumors 1. They usually occur in adult men up to the seventh decade 1.
Risk factors
As in for other mediastinal germ cell tumors Klinefelter syndrome is considered as a risk factor 1,2.
Diagnosis
The final diagnosis is based on histology as well as immunohistochemistry 1.
Diagnostic criteria
The main diagnostic criterion according to the WHO classification is histological evidence of atypical proliferating syncytiotrophoblasts and cytotrophoblasts with dilated vascular sinusoids and frequently areas of hemorrhage and necrosis 1.
A further desirable criterion is the expression of cytokeratins, SALL4, GATA3 and hCG in syncytiotrophoblasts on immunohistochemistry 1.
Diagnostic clues
A large rapidly growing heterogeneous mediastinal mass with pleural and pulmonary invasion in the clinical setting of thyrotoxicosis might be a hint towards the diagnosis.
Clinical presentation
Clinical signs and symptoms include dyspnea, chest pain, cough and hemoptysis as well as superior vena cava syndrome, syncope, headache and cardiac tamponade 1,2. Some patients might present with gynecomastia or thyrotoxicosis 1,3.
Complications
Mediastinal choriocarcinomas might cause the following complications 1-3:
- superior vena cava obstruction
- infiltration of adjacent structures
- pericardial effusion and/or cardiac tamponade
- pleural effusion
- lymph node and distant metastases
- thyrotoxicosis
Pathology
Mediastinal choriocarcinomas are malignant non-seminomatous germ cell tumors primarily composed of syncytiotrophoblasts and cytotrophoblasts. They usually occur in combination with other histologic tumor types 1,2.
Pathogenesis
Mediastinal choriocarcinomas apparently host an isochromosome 12p. A hypothesis is an aberrant midline migration of primordial germ cells 1.
Location
Primary mediastinal choriocarcinomas can be found in the anterior mediastinum and posterior mediastinum 1.
Macroscopic appearance
Mediastinal choriocarcinomas are often large at the time of diagnosis with a soft and fragile consistency, extensive areas of hemorrhage and focal necrotic areas 1,2.
Microscopic appearance
Microscopically mediastinal choriocarcinomas are characterized by the following features 1-4:
- intermingled syncytiotrophoblasts and cytotrophoblasts
- syncytiotrophoblasts: large pleomorphic multinucleated cells with hyperchromatic nuclei
- cytotrophoblasts: medium-sized mononucleated cells with basophilic cytoplasm and eccentric nuclei
- common atypical mitosis and cellular atypia
- dilated vascular sinusoids
- extensive hemorrhage and necrosis
Immunophenotype
Immunohistochemistry stains are usually positive for SALL4, GATA3 and cytokeratins. Syncytiotrophoblasts express glypican-3 hCG and ɑ-inhibin. OCT4, AFP, CEA, PLAP, CD30 and vimentin are usually negative 1.
Radiographic features
Descriptions of imaging features of mediastinal choriocarcinomas are scarce. They are described as heterogeneous and characterized by hemorrhagic and necrotic areas 2,3.
Plain radiograph
Chest x-rays might show widening of the anterior mediastinum.
CT
On chest CT, mediastinal choriocarcinomas have been described as well-defined and heterogeneous with areas of hemorrhage and/or necrosis 3. Pleural or pericardial effusions might be present.
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
- associated complications (e.g. superior vena cava obstruction, pleural or pericardial effusion)
- nodal disease
- distant metastases
Treatment and prognosis
Management includes cisplatin-based chemotherapy and possibly surgery. Prognosis is poor with a short overall survival time of months 1, 3-5.
Differential diagnosis
Condition or tumors that might mimic the appearance of tumors include 1:
- lymphoma
- thymoma
- thymic carcinoma
- other mediastinal germ cell tumors
- metastatic carcinoma
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