Thymoma

In medicine (oncology), thymoma is a neoplasm of the thymus. It is a rare disease, best known for its enigmatic association with the neuromuscular disorder myasthenia gravis. There are benign and malignant forms, which present similarly. more...

Signs and symptoms

• 33%-50% is detected accidentally on routine X-rays of the chest.
• 33% presents with complaints due to compression of surrounding structures by the expanding tumor:
  • Vena cava superior syndrome (compression of the upper caval vein)
  • Dysphagia (trouble swallowing)
  • Cough, chest pain
• A final 33% has autoimmune symptoms; thymomas in these are usually benign. The best known is myasthenia gravis, of which 25-50% is associated with a thymoma. Some others are: pure red cell aplasia and Good's syndrome (thymoma with combined immunodeficiency and hypoimmunoglobulinemia G).
  • Rare associations that have been reported are: acute pericarditis, Addison's disease, agranulocytosis, alopecia areata, ulcerative colitis, Cushing's disease, hemolytic anemia, limbic encephalopathy, myocarditis, nephrotic syndrome, panhypopituitarism, pernicious anemia, polymyositis, rheumatoid arthritis, sarcoidosis, scleroderma, sensorimotor radiculopathy, stiff person syndrome, systemic lupus erythematosus and thyroiditis.

Malignant thymomas can metastasize, generally to pleura, kidney, bone, liver or brain.

Diagnosis

When a thymic pass is identified, the diagnosis is achieved with histology (obtaining a tissue sample of the mass). When a thymoma is suspected, a CT/CAT scan is generally performed to estimate the size of the tumor, and can be biopsied with a CT-guided needle. Although there is a risk of pneumomediastinum, mediastinitis and the risk of damaging the heart or large blood vessels.

The tumor is generally located inside the thymus, and can be calcified. Increased vascular enhancement can be indicative of malignancy, as can be pleural deposits.

If the suspicion is real, some blood tests are often performed to gain an appreciation of associated problems or possible spread. These include: full blood count, protein electrophoresis, antibodies to the acetylcholine receptor (indicative of myasthenia), electrolytes, liver enzymes and renal function.

The final diagnosis is made by removing the thymus. Pathological investigation of the specimen will reveal if the tumor was benign or malignant.

Pathophysiology

Thymomas originate from the epithelial cell population in the thymus. Many subtypes are recognised, some of which have a better- or worse-than-general prognosis.

Epidemiology

Men and women are equally affected. The main age for thymomas is 30-40, although cases have been described in every age group.

Treatment

Surgery is the mainstay of treatment. If the tumor was benign and was removed in its entirety, no further therapy is necessary. Malignant tumors may need additional treatment with radiotherapy, or sometimes with chemotherapy (cyclophosphamide, doxorubicin and cisplatin).

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