Quantification of Mucosal Mast Cells in the Gastrointestinal Tract A Primer for Practicing Pathologists

• Context.—Mast cells are essential components of the immune system and play crucial pathogenetic roles in several digestive diseases, including mastocytic enterocolitis and eosinophilic gastrointestinal disorders. Pathologists have rarely been asked to evaluate the distribution and density of mast cells in gastrointestinal (GI) biopsy specimens. However, such requests are becoming more common because of an increasing awareness of the role of mast cells in functional GI disease and in both esophageal and nonesophageal eosinophilic gastrointestinal disorders. Objective.—To provide pathologists with tools to incorporate the assessment of mast cells in the evaluation of esophageal, gastric, and intestinal specimens by developing a systematic approach to their evaluation, counting, and reporting. Design.—This study consisted of a review of the literature followed by multiple consensus sessions to decide where to count mast cells and what a countable mast cell is. Results.—We reviewed 135 papers addressing the content of mast cells in the digestive tract, selected 21 that detailed how cells were counted (microscope lens, area of high-power fields, locations evaluated, type of cells considered as countable), and summarized their data in a table. Then, drawing from both the acceptable literature and our own extensive experience, we reached a tentative consensus on: (1) the normal numbers in the different segments of the GI tract; (2) the morphology of countable mast cells; and (3) the locations and strategies for counting them. Conclusions.—The result is a set of suggestions for reporting mast cell counts, their distribution, and their location in a way clinicians can understand and use for management decisions.