Intestinal Pseudo-Obstruction Workup

Updated: Jul 23, 2018
  • Author: Burt Cagir, MD, FACS; Chief Editor: John Geibel, MD, MSc, DSc, AGAF  more...
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Workup

Approach Considerations

Laboratory investigations generally are of little diagnostic value for intestinal pseudo-obstruction (also referred to as acute colonic pseudo-obstruction [ACPO] or Ogilvie syndrome]). The diagnosis is based largely on the clinical signs and symptoms, the natural history of the condition, and the findings from radiographic studies. [42]

Plain radiography is the most useful diagnostic tool in this setting. If plain radiography fails to confirm the diagnosis, a contrast enema may be used. Contrast enema should also be used in cases to rule out mechanical colonic obstruction. Although computed tomography (CT) is not required to establish a diagnosis, it may be helpful for excluding the presence of frank perforation, obstruction, and toxic megacolon. [43]

Colonoscopy may be helpful not only diagnostically but also therapeutically. This procedure can help exclude an obstructive process and decompress the colon.

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Laboratory Studies

A complete blood count (CBC) is indicated. A finding of leukocytosis should raise concerns for possible impending or frank perforation. However, it should be kept in mind that leukocytosis is found in the presence of viable as well as ischemic bowel and is therefore nondiagnostic of intestinal pseudo-obstruction. [2, 14]

Mild electrolyte imbalances are often present and typically signify dehydration. [27] Hyponatremia and hypokalemia can be present and reflect a consequence of the pathologic condition, rather than its etiologic factor. [2, 8, 14, 25] Patients frequently exhibit prerenal azotemia or renal insufficiency.

A liver function profile may be helpful.

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Plain Abdominal Radiography

Aside from physical examination, the most useful screening test for intestinal pseudo-obstruction is plain abdominal radiography. [41] Films show a dilated colon, with dilatation often extending from the cecum to the splenic flexure and occasionally to the rectum (see the images below). Serial films may be used to follow the clinical course and the response to treatment.

Abdominal radiographs confirm acute colonic pseudo Abdominal radiographs confirm acute colonic pseudo-obstruction after hip surgery. Note extensive, diffuse colonic dilation with no evidence of transition point.
Ogilvie syndrome. Ogilvie syndrome.

The most common finding is massive colonic dilatation involving the cecum and the ascending and transverse colon. Progressive colonic dilatation can lead to marked increases in cecal distention. By the Laplace law, the tensile strength of the colonic wall will be exceeded first in that portion of the colon that has the greatest diameter—namely, the cecum. [13] Thus, the cecum is the most common site of perforation in colonic pseudo-obstruction. [16, 27]

Although no agreement has been reached regarding the absolute cecal diameter that results in perforation, most investigators agree that the risk of perforation is markedly increased with cecal diameters in the range of 12-14 cm. [13, 14, 16, 33, 37] Therefore, frequent abdominal radiographs to assess the diameter of the cecum are useful in the management of these patients.

The transition between dilated and collapsed bowel is usually near the splenic flexure but can occasionally occur in the distal or sigmoid colon. [27, 37, 44]

Air-fluid levels are only occasionally observed; small bowel dilatation can occur, but this relies on the incompetency of the ileocecal valve. [2, 8, 14, 29, 45]

Other radiologic features include well-defined colonic septa, a smooth contour of the inner lumen, and preservation of haustral markings. [16, 37, 45, 46]

Differentiating colonic pseudo-obstruction from true obstruction is sometimes difficult. A 1995 study suggested using a prone lateral view of the rectum to help confirm the diagnosis. [47] Placing patients in the right lateral decubitus position for several minutes to allow gas to pass into the distal colon facilitated gaseous filling of the rectum when patients were positioned for a prone lateral view of the pelvis. This approach had a 75% success rate in excluding mechanical obstruction, and gaseous filling did not occur in any patients with mechanical obstruction. [47]

An abdominal CT scan is very helpful to confirm the diagnosis by excluding mechanical obstruction and toxic megacolon.

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Contrast Enema

If the diagnosis cannot be confirmed by means of plain radiography or physical examination, a contrast enema may be used. Common enemas include barium and diatrizoate meglumine. Both of these contrast materials are contraindicated in the presence of perforation. Because of the risk of perforation, the contrast material should be introduced under low pressure. No air is required, and the examination may be terminated when the dilated colon is reached.

Diatrizoate meglumine has advantages over barium in that it is clear and water-soluble. In addition, it can be more easily washed away at the time of colonoscopy and can often be therapeutic because of its hyperosmolarity, which results in fluid shifts into the lumen and may subsequently increase colonic motility. Furthermore, it removes the risk of peritoneal contamination with barium if a perforation occurs or a laparotomy becomes necessary. [16, 30, 48, 49, 50]

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Colonoscopy

Flexible colonoscopy can differentiate colonic pseudo-obstruction from mechanical colonic obstruction and can also serve a therapeutic function when colonic decompression is performed during diagnostic colonoscopy. If a mechanical condition is identified as the cause of colonic obstruction during the diagnostic procedure, biopsy of the colonic mass can also be accomplished via flexible colonoscopy. The procedure may be challenging to perform in many patients because of the difficulty of accomplishing adequate bowel preparation.

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