Birbeck granules in the cytoplasm is characteristic of-

Birbeck granules are seen in the langerhans cells. Langerhans cell histiocytosis,earlier called as histiocytosis -x is the monoclonal proliferation of langerhans cells. Langerhans cell histiocytosis includes 3 clinicopathologically related conditions occurring in children :eosinophilic granuloma, Hand-schuller-christian disease, and letterer-siwe syndrome. Electron microscopic examination of these conditions demonstrate histiocytosis-x bodies or birbeck granules in the cytoplasm. These are rod shaped structures having dilated tennis racket like terminal end. Their function is not known but they arisefrom receptor mediated endocytosis of langerin found in human epidermal cells, a protein involved in Birbeck granule biosynthesis. Ref:Harsh Mohan textbook of pathology 7th edition.Pg no365,366.