Question: A 77-year-old man presented with progressive dyspnea, lower extremity edema, and worsening abdominal distention. He denied chest pain, abdominal pain, nausea, vomiting, weight loss, fever, or chills. He reported daily bowel movements. He has a history of aortic valve replacement for severe aortic stenosis, paroxysmal atrial fibrillation, right hepatic lobectomy for right hepatic lobe hepatocellular carcinoma, sigmoid diverticulosis, and chronic colonic dilation of unclear etiology. His physical examination was remarkable for diminished breath sounds bilaterally, a severely distended abdomen without peritoneal signs, and bilateral lower extremity edema. Laboratory investigations were remarkable for mild normocytic anemia with hemoglobin (12.6 g/dL) and mean corpuscular volume (84.6 fL), elevated alkaline phosphatase (168 IU/L), international normalized ratio (1.7), and brain natriuretic peptide (298 pg/mL), and otherwise normal troponin (0.01 ng/mL), lactic acid (1 mmol/L), white blood cell count (10.7 K/μL), potassium (3.8 mEq/L), phosphorus (4 mg/dL), and magnesium (2.1 mg/dL). An echocardiogram showed normal right and left ventricular function with no evidence of valvular dysfunction. Chest computed tomography (CT) angiography of the chest showed low lung volumes with elevation of the right hemidiaphragm and no evidence of pulmonary embolism. An abdominal CT scan with intravenous contrast revealed a severely distended colon from the proximal ascending to mid sigmoid colon (maximum transverse colonic diameter of 22.4 cm) with mass effect on the abdominal structures and right heart (Figure A, B), abrupt narrowing of the mid sigmoid colon with decompressed distal sigmoid colon and rectum, and sigmoid colon diverticulosis without radiographic evidence of diverticulitis. A flexible sigmoidoscopy performed for colonic decompression and to rule out anatomic lesions revealed sigmoid colon diverticulosis with severe narrowing of the mid sigmoid colon at 25 cm from the anal verge (Figure C) and markedly dilated colon proximal to the narrowing (Figure D). What is the most likely diagnosis and what are the next steps in management? See the Gastroenterology web site (www.gastrojournal.org) for more information on submitting your favorite image to Clinical Challenges and Images in GI. After careful endoscopic inspection, there was no evidence of mucosal inflammation or an obvious mass in the sigmoid colon and the findings were most consistent with sigmoid stenosis related to chronic diverticulitis causing megacolon. Because the patient was symptomatic owing to the extrinsic compression effect of the massively dilated colon on the surrounding organs and owing to concern for impending colonic rupture, the decision was made to proceed with surgery. He underwent an urgent exploratory laparotomy with total abdominal colectomy with end-ileostomy. Intraoperatively, the ascending, transverse, descending, and sigmoid colon seemed to be massively dilated to approximately 4 cm below the peritoneal reflection with abrupt tapering to the normal rectum (Figure E, F). Histologic findings of the resected colon and ileum demonstrated ischemic changes, submucosa hemorrhage, mural fibrosis, and diverticula in the colon with ganglion cells present throughout the colon and ischemic changes in the terminal ileum. Colonic diverticulosis is a common disease of the elderly and can be classified as either uncomplicated or complicated.1Peery A.F. Shaukat A. Strate L.L. AGA clinical practice update on medical management of colonic diverticulitis: expert review.Gastroenterology. 2021; 160: 906-911.e1Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar,2Hanna M.H. Kaiser A.M. Update on the management of sigmoid diverticulitis.World J Gastroenterol. 2021; 27: 760-781Crossref PubMed Scopus (16) Google Scholar Complicated diverticulitis is characterized by colonic inflammation and associated perforation, abscess formation, fistulation, or stricture formation.1Peery A.F. Shaukat A. Strate L.L. AGA clinical practice update on medical management of colonic diverticulitis: expert review.Gastroenterology. 2021; 160: 906-911.e1Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar,2Hanna M.H. Kaiser A.M. Update on the management of sigmoid diverticulitis.World J Gastroenterol. 2021; 27: 760-781Crossref PubMed Scopus (16) Google Scholar Stricture formation leading to large bowel obstruction is a rare complication of diverticulitis and patients may present with either acute or chronic large bowel obstruction.1Peery A.F. Shaukat A. Strate L.L. AGA clinical practice update on medical management of colonic diverticulitis: expert review.Gastroenterology. 2021; 160: 906-911.e1Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar, 2Hanna M.H. Kaiser A.M. Update on the management of sigmoid diverticulitis.World J Gastroenterol. 2021; 27: 760-781Crossref PubMed Scopus (16) Google Scholar, 3Antonopoulos P. Almyroudi M. Kolonia V. et al.Toxic megacolon and acute ischemia of the colon due to sigmoid stenosis related to diverticulitis.Case Rep Gastroenterol. 2013; 7: 409-413Crossref PubMed Scopus (6) Google Scholar Distension of the colon owing to chronic stenosis can lead to continuous ischemia of the colon segment proximal to the obstruction and subsequent necrosis.3Antonopoulos P. Almyroudi M. Kolonia V. et al.Toxic megacolon and acute ischemia of the colon due to sigmoid stenosis related to diverticulitis.Case Rep Gastroenterol. 2013; 7: 409-413Crossref PubMed Scopus (6) Google Scholar There are very few reports in the literature reporting toxic megacolon and ischemia–necrosis of the colon owing to diverticulitis-related sigmoid stricture.3Antonopoulos P. Almyroudi M. Kolonia V. et al.Toxic megacolon and acute ischemia of the colon due to sigmoid stenosis related to diverticulitis.Case Rep Gastroenterol. 2013; 7: 409-413Crossref PubMed Scopus (6) Google Scholar In general, in the absence of acute surgical abdomen, there is consensus for elective surgery as the definitive treatment of complicated diverticulitis with symptomatic colonic stricture given it is unlikely to resolve without surgical intervention.2Hanna M.H. Kaiser A.M. Update on the management of sigmoid diverticulitis.World J Gastroenterol. 2021; 27: 760-781Crossref PubMed Scopus (16) Google Scholar