Ischemic colitis (IC) is an ischemic injury to the colon caused by an occlusive arterial blood supply or blocked venous return. Colonoscopic manifestations most frequently include colonic mucosal edema and erosion, while tubular channels are rare. It is also known as colon cast, and doctors often misdiagnose it when they encounter it. The present study presents a rare form of IC. An 80-year-old man visited The Affiliated People's Hospital of Ningbo University (Ningbo, China) due to abdominal pain and bloody stools. He had no significant comorbidities and had not taken medication. Physical examination suggested tenderness in the left lower abdomen. Abdominal computed tomography (CT) showed thickening of the sigmoid colon wall. Laboratory tests showed positive fecal occult blood, whereas routine blood tests, including blood coagulation, were normal. Diagnostic colonoscopy revealed sigmoid colon narrowing. There was a long strip of tissue in the sigmoid with a cystic and smooth head, the base of the pedicle was edematous and anabrotic. Abdominal CT angiography revealed no abnormality of the mesenteric artery. The day after colonoscopy, the patient expelled a 17-cm strip of tissue from his anus. Pathological examination revealed inflammatory necrotic colonic mucosa. After 1 week, repeat colonoscopy revealed the strip had been shed, the sigmoid mucosa was edematous and anabrotic, but other intestinal segments were normal.