J Pathol Transl Med.  2021 Sep;55(5):349-354. 10.4132/jptm.2020.05.17.

Appendiceal actinomycosis mimicking appendiceal tumor, appendicitis or inflammatory bowel disease

• Sung YN
• Kim J

• KMID: 2520174
• DOI: http://doi.org/10.4132/jptm.2020.05.17

Abstract

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.

Keyword

Appendix; Actinomycosis; Mycetoma; Pathology

Figure

• 

  Fig. 1. Radiologic, colonoscopic, and gross features. (A) Contrast-enhanced computed tomography of case No. 1 shows appendicolith, fat infiltration with prominent wall thickening with contrast enhancement in the appendiceal base (arrow). (B) The resected appendix shows marked mural thickening, dilated appendiceal lumen and central fecalith. (C) Colonoscopic image of case No. 2 shows an approximately 10 mm-sized hyperemic mucosal bulging around the appendiceal orifice. (D) Cut surface of the resected specimen shows mucosal bulging (about 1.0cm in great dimension) on the orifice of appendix (arrow).

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  Fig. 2. Representative microscopic pictures. (A) Chronic transmural inflammation with scattered lymphoid follicles or aggregates are observed. (B) The bulging mucosa in colonoscopy is hypertrophic fibroadipose tissue that is covered by inflamed mucosa. (C) One of the fibroinflammatory foci shows marked lymphoplasmacytic infiltration with fibrosis that is reminiscent of inflammatory pseudotumor. (D) The inflamed mucosa of the appendix shows marked lymphoplasmacytosis, crypt abscess, and crypt distortion. (E) An actinomycotic colony is surrounded by mixed inflammatory cell infiltrates. (F) The filamentous nature is better demonstrated by Periodic acid–Schiff staining.

Reference

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