A 46-year-old woman who underwent restorative proctocolectomy 5 years ago for a history of familial adenomatous polyposis is admitted for persistent abdominal pain of 3 months’ duration, nausea, vomiting, and progressive distention of her abdomen. She typically has 4 to 6 bowel movements per day but has recently been having only 1 to 2 watery bowel movements. Computed tomography of the abdomen demonstrates dilated loops of proximal bowel with air fluid levels. There is also a 10×10–cm mass at the root of the small-bowel mesentery near a clear transition point with decompressed distal small bowel. Nasogastric tube decompression has started. Which of the following is the most appropriate management strategy?