Acute Large Bowel Obstruction

1

What are the mechanical causes of large bowel obstruction (LBO)?

The most common mechanical causes are carcinoma (50%), volvulus (15%), adhesions (15%), and diverticular disease (10%). Extrinsic compression from metastatic carcinoma or noncolonic neoplasms is another cause of obstruction. Less frequent causes include hernia with colonic incarceration, intussusception, benign tumor, fecal impaction, inflammatory bowel disease, ischemic colitis, adhesions, bezoars, and retroperitoneal fibrosis.

2

How is the diagnosis made?

• a.

  The patient complains of crampy abdominal pain, bloating, and obstipation. Nausea and vomiting occur later in LBO and may be feculent. An acute onset of symptoms is more consistent with volvulus compared with the gradual development of obstructive complaints from patients with colon carcinoma. Longer duration of symptoms suggest a malignant etiology for LBO.

• b.

  Physical examination reveals abdominal distention and high-pitched bowel sounds. Rectal examination may reveal an obstructing rectal cancer or evidence of fecal impaction. Absence of bowel sounds and localized tenderness may be signs of peritonitis. Progression of symptoms accompanied by a high fever or tachycardia requires immediate operative attention.

• c.

  Flat and upright abdominal radiographs reveal dilated colon proximal to the obstruction. An upright chest radiograph may show free air under the diaphragm if a perforation has occurred.

3

How is the diagnosis confirmed?

Modern fast acquisition helical multidetector CT (MDCT) imaging has replaced contrast enema for confirming the diagnosis of LBO in many patients. MDCT has a reported sensitivity and specificity of 96% and 94%, respectively, in the diagnosis of LBO. Computed tomography (CT) scans may distinguish between mechanical obstruction or pseudo-obstruction and can help with the diagnosis of diverticulitis or colon carcinoma. CT scans can help distinguish between sigmoid and cecal volvulus. MDCT can show a transition point with proximal dilated colon and collapsed distal colon. An intraluminal or rectal mass can also been seen. In addition, multifocal or metastatic disease can been demonstrated. CT avoids the risk of perforation with instrumentation during enema or endoscopy, and may be of benefit in elderly or frail patients who cannot cooperate with or tolerate other diagnostic procedures.

4

What is the role of contrast enemas in the diagnosis of LBO?

A contrast enema (barium or water-soluble contrast) is necessary to delineate the level and nature of an obstruction. A volvulus can be identified by a “bird’s beak” narrowing at the neck of the volvulus. Sigmoidoscopy or colonoscopy is an essential part of the evaluation; it allows visualization of the colon and may be therapeutic in the case of a sigmoid volvulus.