Review Question - QID 103017

The patient with colicky abdominal pain has an abdominal radiograph suggestive of small bowel obstruction. The most common underlying cause of small bowel obstruction is abdominal adhesions that develop after abdominal surgeries.

Small bowel obstructions results from the external or internal compression of the bowel wall. Bowel contents accumulate proximal to the obstruction while the distal bowel becomes decompressed. As bowel contents accumulate, the proximal bowel becomes increasingly distended, resulting in bowel wall edema, and eventual ischemia and necrosis. As the bowel wall becomes ischemic, perforation may occur which results in peritonitis and sepsis. Patients typically present with colicky abdominal pain, and report a lack of bowel movements and passage of gas. Abdominal distention is a common exam finding, along with high pitched bowel sounds. The most common cause of small bowel obstruction is from the formation of adhesions as a result of prior abdominal surgeries. Historically, abdominal wall hernias were the most common cause, but are now a less common cause due to early detection and the ease of hernia repair. Colon cancer or other abdominal masses, inflammatory bowel disease, and prior abdominal wall radiation may also result in small bowel obstruction. The most appropriate initial diagnostic test for patients with suspected small bowel obstruction is an upright abdominal radiograph that will demonstrate small bowel distention with or without air-fluid levels. CT imaging of the abdomen and pelvis may subsequently be obtained to better characterize the obstruction. Treatment includes fluid resuscitation, NPO status, and nasogastric tube placement for most patients. Some patients may be managed non-operatively with bowel rest and fluid resuscitation. Other patients will require surgical intervention, especially if perforation has occurred or bowel ischemia is suspected.

Jackson and Raiji discuss the evaluation and treatment of small bowel obstruction. They present an algorithm for management (Illustration A) and suggest that the most common causes of SBO are adhesions, neoplasms, and herniations, with adhesions causing approximately 60% of cases.

Ten Broek et al. performed a systematic review and meta-analysis of complications of post-operative adhesions. They report that the incidence of small bowel obstruction by any cause after abdominal surgery is 9%, while adhesion-related small bowel obstruction occurred 2% of the time.

Illustration A demonstrates an algorithmic approach to management of small bowel obstruction.

Incorrect answers:
Answer 1: Abdominal wall hernias were historically a common cause of small bowel obstruction. However, this is no longer the case due to early recognition and repair of abdominal wall hernias.

Answer 2: Colon cancer may cause small bowel obstruction due to extrinsic compression of the small bowel. However, adhesion formation from prior abdominal surgery is still a more common cause of small bowel obstruction.

Answer 3: Patients with a history of abdominal radiation may also develop small bowel obstruction due to the formation of abdominal adhesions. However, prior abdominal surgery is still a more common cause of abdominal wall adhesion formation, and therefore a more common cause of small bowel obstruction.

Answer 4: Inflammatory bowel disease such as Crohn disease may result in small bowel obstruction due to the formation of luminal small bowel strictures. However, it is a less common cause of small bowel obstruction and is unlikely in this elderly patient.

Bullet Summary:
The most common underlying cause of small bowel obstruction is abdominal adhesions that develop after abdominal surgeries.