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Thymic Lesion

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Overview Thymic tumors occupy the anterior mediastinum, which is immediately posterior to the sternum and the anterior surface of the pericardium and great vessels. Tumors of thymic, lymphatic, or germ cell origin most commonly occur in this compartment, although aberrant parathyroid or thyroid tissue masses are sometimes found, along with vascular and mesenchymal tissue masses. (See the images below.) Fairly large thymus in an infant.  View Media Gallery Gross appearance of a thymoma showing distinct multinodularity and scattered, focal cystic changes.  View Media Gallery Thymolymphoma. Chest radiograph shows a large, lobulated mediastinal mass.  View Media Gallery About one half of all thymic tumors are malignant in individuals aged 20-40 years, and one third are malignant in persons younger than 20 years and those older than 40 years. (A malignant thymic tumor is seen in the image below.) Malignant thymoma. Chest CT scan in a 61-year-old man with myasthenia gr
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Types Of Hyperplasia

There are two forms of thymic hyperplasia:  1- True thymic hyperplasia (or rebound hyperplasia), in which there are normal proportions of glandular/ lymphoid elements in an enlarged gland secondary to rebound following stress-related atrophy, illness, or immune suppression (following chemotherapy or discontinuation of corticosteroid administration) [15,19]. When the body is exposed to stress the thymus may shrink to as little as 40% of its original volume (depending on the severity and duration of the stress) [20]. Once the body recovers, the thymus can usually grows back to its original size within 9 months, but it can grow to be as much as 50% larger [20]. Approximately 10-25% of patient who undergo chemotherapy may develop rebound hyperplasia [20].  Most cases of thymic hyperplasia secondary to chemotherapy occur within a year or two and the gland typically returns to normal size [8,20]. Because of bolstered cell-mediated immunity, thymic hyperplasia has been associated with a g
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