A one year old boy presented with hepatosplenomegaly and delayed milestones. The liver biopsy and bone marrow biopsy revealed presence of histocytes with PAS positive. Electron microscopic examination of these histiocytes is most likely to reveal the presence of -

Ans. is 'a' i.e., Birbeck granules in the cytoplasm o Hepatosplenomegaly, presence of histiocytes with PAS postive suggest the diagnosis of langerhans cell histiocytosis. o Diagnosis of LCH The hallmark of LCH is clonal proliferation of cells of monocyte lineage. The presence of Birbeck granules in the cytoplasm of tumor cells is characteristic of LCH. Birbeck granules are tennis racket shaped bilamellar granules. As Birbeck granules are not seen in all tumor cells by election microscopy, the detection of S-100 and CD1a expression by immunohistochemical techniques makes the definitive diagnosis.