An otherwise healthy 37-year-old woman was initially seen in the emergency department complaining of lower abdominal pain, nausea, and vomiting of 3 days' duration. She described previous episodes of right upper quadrant abdominal pain. On physical examination, she was febrile and tachycardic with lower abdominal tenderness, and her rectal examination results were Hemoccult negative. The laboratory evaluation was significant only for an elevated white blood cell count, and an abdominal radiograph revealed distended large-bowel loops. A computed tomographic scan revealed a large mass in the sigmoid colon (Figure 1).