A 23-year-old woman with a history of an eating disorder complains of vomiting, nausea, and severe abdominal pain. Physical examination shows abdominal distension and constipation. An X-ray film of the abdomen reveals air-fluid levels and a hyperlucent shadow at the epigastric area. The material obstructing the gastrointestinal tract is removed surgically and shown. Which of the following is the most likely diagnosis?