Eosinophilic, Mastocytic, and Histiocytic Diseases of the Gastrointestinal Tract

Primary eosinophilic, mastocytic, and histiocytic disorders of the gastrointestinal (GI) tract comprise a spectrum of poorly understood and rare entities. Despite their extremely low prevalence in the general population, these diagnoses are commonly considered in the differential diagnosis when evaluating GI biopsies in daily practice. Surgical pathologists will often encounter biopsies with a prominence of one or more of these cell types. The question that then arises is whether the patient actually has one of these rare disorders or the findings are a secondary manifestation of mucosal injury due to an unrelated etiology. The aim of this chapter is to provide a pragmatic approach to interpretation of GI biopsies when faced with an inflammatory process with prominence of these cell types and to highlight our evolving understanding of these disorders that affects clinical practice.