MULTILOCULAR THYMIC CYSTS IN CHILDREN WITH HUMAN-IMMUNODEFICIENCY-VIRUS INFECTION - CLINICAL AND PATHOLOGICAL ASPECTS

Background: Children with human immunodeficiency virus (HIV) infection have an increased susceptibility to severe and unusual infections, ma lignancies, and disorders characterized by abnormal lymphoproliferatio n (e.g., lymphoid interstitial pneumonitis). We report a novel disease entity associated with pediatric HN infection that is characterized b y massive enlargement of the thymus as a result of lymphoid hyperplasi a and multicystic changes. Methods: Eight patients with HIV infection and cystic enlargement of the thymus are subject of this report. The s tatus of their HIV disease and its clinical and radiologic manifestati ons at the time of diagnosis of the mediastinal mass are described. Ti ssue specimens mere obtained from six patients and examined by microsc opy and immunohistochemistry, The specimens were also evaluated for th e evidence of HIV and Epstein-Barr virus by in situ hybridization. Res ults: Patients were between 2.1 and 12.1 years of age, with CD4(+) cel l counts between 102 and 733 cells/mm(3). In all eight cases an anteri or mediastinal mass was discovered incidentally on radiography of the chest, and computed tomography of the chest revealed a multicystic app earance. Histologic examination demonstrated distortion of the thymic architecture by focal cystic changes, lymphoid follicular hyperplasia, diffuse plasmacytosis, and multinucleated giant cells. In situ hybrid ization revealed HIV particles on the surface of follicular dendritic cells. Further, results of in situ hybridization for EBV were positive in lymphoid cells from biopsy samples of four patients. The patients were followed between 8 months and 4.8 years. In five patients the mas s either decreased in size or resolved completely. Conclusions: We des cribe a series of children with HN infection and multilocular thymic c ysts. We hypothesize that aberrant immunoregulation in these HIV-infec ted children leads to follicular hyperplasia and multicystic changes i n the thymus, causing massive enlargement. EBV infection might also co ntribute to the pathogenesis of this process. Because none of our pati ents had symptoms from the mass, and there was no evidence of malignan cy in the examined biopsy samples, it seems prudent to manage such chi ldren with careful follow-up examinations.