Acute eosinophilic appendicitis and the significance of eosinophil - Edema lesion.

Eight cases of a histological entity that we name 'acute eosinophilic appendicitis' (AEA) are described and compared with classical acute appendicitis and appendices, which turned out to be normal after emergency appendicectomy. These 8 cases formed part of a dataset of 128 emergency appendicectomies, which also included 78 cases of classical acute appendicitis and 42 cases of normal appendix. The clinical and pathological variables were compared between these three. Acute eosinophilic appendicitis is characterized by acute presentation and a grossly inflamed appendix, but with absence of neutrophils in the muscle layer. The histological hallmark of the entity is eosinophil infiltration of the muscularis propria with accompanying edema separating muscle fibers (the Eosinophil - Edema lesion). The duration and prevalence of symptoms, the male female ratio and the gross maximum circumference of the appendix in these 8 cases resembled classical acute appendicitis rather than those cases in which the morphology of the appendix was normal. The Eosinophil-Edema lesion was also seen in many cases of classical appendicitis in non-suppurative areas where neutrophils were sparse or absent. We hypothesize that this lesion is an allergic response and is probably an early event in the evolution of acute phlegmonous appendicitis. Acute eosinophilic appendicitis may merely be those cases that do not proceed on to suppuration.