Invasive Moderately-Differentiated Mucinous Adenocarcinoma Incidentally Identified in Perforated Acute Diverticulitis With Abscess Formation

Abstract

Colonic adenocarcinoma rarely arises within a diverticulum. As illustrated in this case report, 
such an occurrence presents difficulties in diagnosis, posed by the overlap of radiological findings in diverticulitis and adenocarcinoma and the potential absence of luminal lesion. Here we 
present a 77-year-old male with acute left lower abdominal pain, fever and leukocytosis. Computarized tomography (CT) imaging revealed extensive colonic diverticulosis, with sigmoid 
colon wall thickening, extraluminal air and a pericolic abscess. No enlarged lymph nodes were 
detected. The clinical diagnosis was acute sigmoid diverticulitis with micro-perforation and abscess formation. Partial sigmoidectomy was performed and diverticulitis confirmed; no tumor 
was identified in the resected colon. However, fragments of mucinous adenocarcinoma were 
incidentally recognized in the pericolic abscess contents. Immunohistochemical (IHC) studies 
supported a primary colonic adenocarcinoma, warranting further clinical workup. A subsequent 
distal sigmoidectomy revealed moderately-differentiated mucinous adenocarcinoma invading 
through the visceral peritoneum, and arising in a low-grade mucinous neoplasm within a diverticulum. The case illustrates that in a patient with diverticulitis and no evidence of a luminal 
neoplasm, the unexpected finding of adenocarcinoma in the resected bowel may be attributable 
to adenocarcinoma arising within a diverticulum