Bowel Obstruction

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Key points

  • Mechanical bowel obstruction is responsible for 15% of hospital admissions for the acute abdomen in the United States.

  • Clinical features and plain abdominal radiographic findings are insufficiently accurate for the diagnosis of intestinal obstruction and its complications, such as ischemia and strangulation.

  • Multidetector computed tomography has emerged as the best single imaging examination for the diagnosis of mechanical bowel obstruction and its complications and can help triage patients to

Pathophysiology

Bowel obstruction causes distention of the gut through the accumulation of both gas and fluid. The gas that accumulates proximal to the obstruction is primarily swallowed air, reflected by its high nitrogen content (70%–80%) and the contribution of bacterial gas is thought to be small. The fluid and gas cause increased intraluminal pressure and distention of the bowel that also affect the motility of the intestine: initially causing increased peristalsis and then leading to decreased

Clinical features

The cardinal symptoms of bowel obstruction are pain, nausea and vomiting, abdominal distention, and decreased stool and flatus. The pain is classically colicky in nature, reflecting increased peristaltic activity as the bowel distends in response to the obstruction. The initial increase in motility is later replaced by reduced activity as the bowel relaxes and dilates, so the colicky pain may be replaced by a more constant pain. If the obstruction is more proximal, the pain may be relieved by

Plain Abdominal Radiographs

The plain radiograph of the abdomen has traditionally been used as the first radiologic study in the workup of acute abdominal pain and suspected bowel obstruction (Box 2). These radiographs may confirm the diagnosis, locate the site of obstruction, and, in some cases, identify the nature of the obstructing lesion. The bowel is usually dilated proximal to the obstruction; however, depending on the competency of the ileocecal valve, proximal LBO can mimic SBO (Fig. 2).8

Air-fluid levels may

Adhesions

Adhesions are the most common cause of SBO, accounting for approximately two-thirds of cases. The incidence of SBO from adhesions has increased during the past 30 years because of the increasing number of laparotomies. Although adhesions form in more than 90% of patients who have undergone laparotomy, only approximately 5% of abdominopelvic surgeries are complicated by SBO. They develop in 0.05% of patients with cesarean delivery, in 1% of patients after appendectomy, and up to 10% of patients

Large bowel obstruction

Mechanical LBO is 4 to 5 times less common than SBO and differs significantly in terms of etiology, pathophysiology, therapy, and prognosis. Colon obstruction is most often the result of a neoplasm, whereas most SBOs are due to adhesions (see Fig. 1, Table 1).6

Summary

The diagnosis and management of patients with bowel obstruction has been revolutionized over the past 2 decades by cross-sectional imaging. Although ultrasound, MR, plain abdominal radiographs and contrast enemas, and small bowel examinations can be useful in certain circumstances, MDCT has evolved as the premier imaging test for patients with known or suspected bowel obstruction. CT findings can be very helpful in determining which patients may benefit from a trial of conservative therapy and

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