This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': '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 –: \nSelect and explain. \nA. Birbeck granules in the cytoplasm, B. Myelin figures in the cytoplasm, C. Parallel rays of tubular structures in lysosomes, D. Electron dense deposit in the mitochondria.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Hepatosplenomegaly, presence of histiocytes with PAS positive suggest the diagnosis of langerhans cell histiocytosis.\n\nDiagnosis of LCH :\n\nThe hallmark of LCII is clonal proliferation of cells of rnonocyte lineage.\nThe presence of Birbeck granules in the cytoplasm of tumor cells is characteristic of LCH.\nBirbeck granules are tennis racket shaped bilamellar granules.\nAs 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.', 'role': 'assistant'}]