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1. What is the role of the thymus gland?
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The thymus gland controls the development of T lymphocytes in the embryo and neonate.
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2. What is the function of the thymus gland in the adult?
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In adult life the thymus is a fat-infiltrated remnant.
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3. Why is the thymus gland of importance to the surgeon?
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It has an ill-understood connection with myasthenia gravis and it is a rather rare site of mediastinal tumour.
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4. Which gland is implicated in the development of myasthenia gravis?
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The thymus gland.
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5. From which tissues do tumours of the thymus gland develop?
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Either from the epithelium (Hassall's corpuscles) or lymphatic tissue, or a mixture of both.
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6. Are tumours of the thymus gland benign or malignant?
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They may be benign or malignant. The thymus may also be involved in cases of lymphoma, particularly Hodgkin’s disease.
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7. What are the three modes of presentation of a tumour of the thymus gland?
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(1) A mediastinal mass. (2) Associated with myasthenia gravis. (3) Associated with immune deficiency states.
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8. In which structure would you find Hassall’s corpuscles?
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This is the epithelium inside the thymus gland.
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9. How would you treat a tumour of the thymus gland?
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Treatment is by thymectomy via median sternotomy, combined with radiotherapy if malignant, to prevent mediastinal recurrence. Early invasion, with no more than pleural and mediastinal fat involvement, carries a good prognosis (90% at 5 years); involvement of the pericardium, great vessels or lung has a poor prognosis.
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10. Which incision would be used to perform a thymectomy?
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Median sternotomy.
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11. What is the prognosis for tumours of the thymus with early invasion to pleural or mediastinal fat?
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Ninety per cent 5 year survival.
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12. Which features are associated with a poor prognosis of thymus tumours?
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Involvement of the pericardium, great vessels or lung.
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13. What is myasthenia gravis?
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This is a condition of muscle weakness apparently due to a defect at the neuromuscular junction in which the motor endplate becomes refractory to the action of acetylcholine owing to the presence of circulating antibodies to the acetylcholine receptor.
