Thymomas account for the vast majority of thymic neoplasms and are often associated with autoimmune or neurologic syndromes, most commonly myasthenia gravis.
About one third of thymomas are asymptomatic and identified as an incidental radiographic finding. A chest computed tomography (CT) with intravenous contrast can be diagnostic.
Small, encapsulated tumors are resected for both pathologic diagnosis and treatment. For anterior mediastinal tumors with a substantial chance of representing lymphoma, core needle biopsy is recommended. Positron emission tomography (PET)/CT scan can be very useful in differentiating thymoma from lymphoma without a biopsy (lymphoma has a far higher maximum standardized uptake value [SUVmax] than noninvasive thymoma).
Thymic malignancies that are locally advanced at presentation are usually treated with induction therapy (chemotherapy ± radiation therapy) followed by reassessment for surgery. Patients with myasthenia gravis should have myasthenic symptoms optimized before surgery.
Thymomas are relatively indolent tumors with high cure rates; however, all thymomas are considered malignant. Prognosis depends largely on completeness of resection, stage (Masaoka-Koga staging system and the 8th edition of the American Joint Committee on Cancer TNM staging system), and WHO histology. Thymic carcinomas and neuroendocrine tumors of the thymus (NETT) are generally more aggressive.
Treatment for locally advanced and metastatic tumors should involve a multidisciplinary team of medical oncologists, thoracic surgeons, radiation oncologists, pathologists, and radiologists who have experience and expertise in thymic malignancies.
Thymic tumors are rare, although they are the most common anterior mediastinal tumors in adults. Thymomas account for the majority of thymic neoplasms. Although smaller tumors are typically asymptomatic and identified incidentally on imaging (unless associated with myasthenia gravis), large tumors can present with chest discomfort, cough, and/or dyspnea, with or without myasthenia gravis symptoms. About one third of thymomas are diagnosed as an incidental finding.
In-depth management of myasthenia gravis is beyond the scope of this topic. See Myasthenia gravis.
History and exam
Key diagnostic factors
- myasthenia gravis
- muscle weakness
- facial and upper extremity edema
- facial plethora
- distended veins in the neck, chest and/or abdominal wall
- left-arm swelling
Other diagnostic factors
- fever and/or weight loss
- history of myasthenia gravis
- age >45 years
1st investigations to order
- chest x-ray
- chest CT with intravenous contrast medium
Investigations to consider
- chest MRI
- tissue biopsy
- acetylcholine receptor antibodies
- PET/CT scan
- serum alpha-fetoprotein (AFP)
- serum beta-human chorionic gonadotrophin (beta-hCG)
locally advanced tumor
- Malignant mediastinal germ cell tumour: seminoma
- Malignant mediastinal germ cell tumour: nonseminoma
- NCCN clinical practice guidelines in oncology: thymomas and thymic carcinomas
- Surgical, radiation, and systemic treatments of patients with thymic epithelial tumours
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