<prompt> Histiocytosis X is seen in except :Hand schuller Christian diseaseEosinophilic granulomaLetter-siwe syndromeTorres syndrome  <response>: Langerhans cell histiocytosis Histiocytosis X :Histocytosis X is characterized by proliferation of Langerhans histiocytes tissue macrophages.It is subdivided into three categories : -Letterer - Siwe syndrome.Hand -Schuller-Christian disease.Eosinophilic granuloma..Tumor cells in each are derived from dendritic cells and express S - 100, CD1a and HLA - DR.The presence of Birbeck granules in the cytoplasm is characteristic.Under the electron microscope, Birbeck granules have a pentalaminar, rodlike, tubular appearance and sometimes a dilated terminal end tennis - racket appearance. 