The role of mast cells in histologically "normal" appendices following emergency appendectomy in pediatric patients.

Fifteen percent to 25% of appendices resected for a preoperative diagnosis of acute appendicitis have no neutrophilic infiltration, thus histologically "normal." The discrepancy between clinical presentation and the lack of definite morphologic changes is confounding. It has been indicated that mast cells may play a role in the pathogenesis of the appendicitis-like pain in patients with histologically negative appendices (HNAs). To investigate whether mast cell density (MCD) is increased in pediatric HNAs, we retrieved 50 appendectomy cases (30 HNA and 20 control, ages 2 days-18 years) in our institute in the last 10 years. All cases were stained with mast cell tryptase by immunohistochemistry, and MCD (count/high-power field) was measured in mucosa, submucosa, muscularis, and serosa. Mast cells had the greatest density in the mucosa, followed by the submucosa, in all appendices. MCDs in all 4 layers were significantly higher in HNAs than in the normal controls (mucosa: 46±9 vs 26±11, P<.01; submucosa: 18±5 vs 11±5, P<.01; muscularis: 6±3 vs 4±2, P<.01; serosa: 6±2 vs 4±2, P<.01). This result suggests that mast cells play an important role in pathogenesis of HNA cases. In clinical practice, pathologists may order immunohistochemical stains for mast cells in cases with no classic histologic findings of acute appendicitis following emergency appendectomy. If increased MCD is noted, the case may be reported as "appendicitis with increased mast cells." This assures surgeons that the appendectomy is the correct treatment and it is not necessary to look for other causes of acute abdomen. This is especially important in children.