Multilocular tuberculous cyst of thymus gland

Clinical Summary A 25-year-old man underwent a preemployment checkup and on chest skiagram was found to have a well-defined opacity in the region of the left hilum. A contrast-enhanced computed tomography (CT) scan of the chest revealed an anterior mediastinal mass of variegated consistency with solid and cystic areas measuring approximately 10.5 6 2.5 cm (Figure 1). There was a loss of plane with the pericardium and the arch of aorta with extension laterally to the upper lobe of the left lung. There was no associated pericardial effusion. The lung parenchyma appeared normal. -human chorionic gonadotropin and alpha-fetoprotein markers as well as thyroid function tests were within normal limits. A CT-guided fine needle aspiration cytology/biopsy was not done because solid areas of the tumor were inaccessible. Based on the preoperative investigations a differential diagnosis of thymic tumor, lymphoma, and tuberculous lymphadenitis was considered. Sternotomy and excision biopsy were planned. At surgery we found a large cystic mass occupying the left lobe of the thymus extending from the innominate vein to the apex of the heart. Laterally the mass was adherent to the upper lobe of the left lung. The pericardial cavity was opened and there were a few solid nodes occupying the area between the arch and the pulmonary artery adherent to the undersurface of the aorta. A frozen section of this mass was reported as TB. The entire cystic mass with the left lobe of thymus was then excised. The left pleura was opened and debulking of the adherent nodes was done to the extent possible. Grossly the specimen measured 11 6 3 cm. On section, it revealed a multiloculated cyst with cyst wall measuring 0.1 cm in diameter. It contained turbid and blood-stained fluid with small warty projections scattered over the inner lining of the cyst. Cut section of the lymph nodes revealed small foci of caseation. Histologically lymph nodes and thymic tissue showed chronic inflammation and multiple granulomas composed of epithelioid histiocytes and Langhans-type giant cells (Figure 2). Central caseous necrosis was present in the lymph nodes. There were no acid-fast bacilli on Ziehl-Neelsen stain. Subsequently the thymic tissue culture was positive for mycobacterium TB. His sputum smear neither showed acid-fast bacilli nor grew Mycobacterium tuberculosis organism on culture. Postoperatively the patient was started on oral antituberculous treatment and recovered well.