Multilocular thymic cyst with epithelioid granulomata of unknown etiology: a radiologic and histopathologic correlation.

Thymic cysts (congenital or acquired) are believed to account for 3% to 5% of all mediastinal masses. Multilocular thymic cysts are an acquired reactive inflammatory process arising within the thymus gland and are less common than the congenital unilocular type. Multilocular cysts have been reported in association with a variety of neoplastic, autoimmune, and infectious conditions. We report a case of a 23-year-old white man who presented with a 2-week history of progressive right-sided shoulder and chest pain. He was found to have an anterior mediastinal mass involving the thymus. This case of multilocular thymic cyst is particularly unique due to the presence of abundant epithelioid granulomata within the cyst, a finding that has not previously been emphasized as a histologic feature of these lesions, and one that expands the histopathologic differential diagnosis, warranting exclusion of infectious and autoimmune etiologies.