[Tissue hypereosinophilia]

Eosinophils are produced in the bone marrow and circulate in the peripheral blood in a quiescent state. After margination and emigration into tissues through postcapillary venules, eosinophils primarily reside in mucosal sites including the gastrointestinal and respiratory tracts. Eosinophilic gastroenteritis and the idiopathic chronic eosinophilic pneumonia, first described by Carrington, are the most characterized idiopathic diseases defined by an eosinophil infiltration restricted respectively to the gastrointestinal and the respiratory tracts. Differential diagnosis can be difficult since several disorders and particularly the idiopathic hypereosinophilic syndrome have many clinical, morphological and histological similarities.