Appendiceal actinomycosis mimicking appendiceal tumor, appendicitis or inflammatory bowel disease.

Appendiceal actinomycosis is very rare and its diagnosis is often difficult even in surgically resected specimens. Here we report two cases of appendiceal actinomycosis confirmed by pathologic examination of surgically resected specimens. Characteristic histologic features included transmural chronic inflammation with Crohn-like lymphoid aggregates and polypoid mucosal protrusion into cecal lumen through fibrous expansion of the submucosa. Chronic active inflammation involved the mucosa of the appendix and cecum around the appendiceal orifice. Crohn's disease with predominant cecal involvement and inflammatory pseudotumor were considered as differential diagnoses. Careful examination revealed a few actinomycotic colonies in the mucosa, confirming the diagnosis. A high index of suspicion with awareness of the characteristic histologic features might prompt careful inspection for the actinomycotic colonies, leading to the appropriate diagnosis of this rare disease.