In medicine,<unk>  is an excessive number of histiocytes (tissue macrophages), and the term is also often used to refer to a group of rare diseases which share this sign as a characteristic. Occasionally and confusingly, the term<unk> " is sometimes used to refer to individual diseases. According to the<unk>  Association of America, 1 in 200,000 children in the United States are born with<unk>  each year. HAA also states that most of the people diagnosed with<unk>  are children under the age of 10, although the disease can afflict adults. The disease usually occurs from birth to age 15.<unk>  (and malignant<unk>  are both important in veterinary as well as human pathology.
Histiocytosis
Non-Hodgkin lymphoma
Angiolymphoid hyperplasia with eosinophilia
Reticulohistiocytoma
Progressive nodular histiocytosis
Intravascular lymphomas
B-cell lymphoma
Tuberculous lymphadenitis