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Abdominal radiology: making the call on the acute abdomen (Proceedings)

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Nov 01, 2009

An enormous amount of information can be obtained from an abdominal radiograph, especially in emergency/critical care situations. The increased availability of abdominal ultrasound has perhaps led to an under-appreciation of the abdominal radiograph. This lecture will review the interpretative steps used to diagnose various abdominal disorders in an emergency setting.

1) Gastrointestinal Mechanical Obstructions: Much of the lecture will review the rules used to diagnose a mechanical obstruction. The importance of this diagnosis is realized when delays to surgery or endoscopy result in increased patient morbidity and mortality. The following important signs of an obstruction should be considered:
     • Size of the Small Intestine: The serosa-to-serosa thickness of a loop of small intestine should not exceed the height of one lumbar vertebral body in dogs and should not exceed TWICE the height of a lumbar vertebral body in cats.
     • Two Populations of Small Intestine: Small intestines become distended orad to (in front of) the site of obstruction while the intestines aboral to the obstruction remain normal. The call can be made regarding an overly distended loop of small intestine when normal loops are nearby. This is an important radiographic sign of "two populations" where one population of bowel is normal and almost completely empty and the other segment is distended (using the rules of the lumbar vertebrae).
     • Stacking and Hairpin Turns: Obstructed intestines will distend (increased size) first. With time, the distended loops will begin to make abrupt, hairpin turns onto themselves and then appear stacked on each other. This generally requires some time after the onset of the obstruction.
     • Persistent gas/fluid pattern with time: Normal bowel is motile and changes in gas/fluid pattern by the second or minute. A persistently gas-filled, oddly shaped loop of bowel is an abnormal finding. Additionally, complete obstructions will prevent the formation of feces in the colon. A persistently empty colon should raise suspicion for mechanical obstruction.

2) Partial Obstructions: Partial obstructions can be a diagnostic challenge. A history of previous intestinal resection and anastomosis surgery in the face of intermittent vomiting is a common presentation for stricture (partial obstruction) of a loop of small intestine. A "gravel sign" is the presence of small mineral opacities aggregating in one segment of mildly distended small intestine. This should raise suspicion for partial obstruction. Mineral fragments (whether due to particles from the floor or maybe cat litter) will evenly disperse throughout the stomach and intestines. These heavier particles tend to settle in front of a partial obstruction, as fluid and less dense particles move beyond the obstruction.

3) Linear Foreign Body Obstructions: The unique aspect of a linear foreign body obstruction is that the size of the small intestines is NOT as important of a sign as the SHAPE. Plicated intestines may not become distended. Instead, the serosal margin becomes undulating and bunched. These plicated intestines can be gas-filled, fluid-filled, or a mixture of both. This applies primarily to cats. Dogs do not ingest thin linear foreign bodies so the appearance of the obstruction differs slightly. Look for the "too many cecums" sign in dogs to diagnose the pantyhose, carpeting, or clothing linear foreign body in a dog. Examples of this will be illustrated.

4) Loss of Serosal Detail: Differentials (both normal and abnormal) for loss of serosal detail will be discussed. Ultrasound is extremely helpful for distinguishing peritoneal effusion from the other causes of serosal detail loss. Concurrent pneumoperitoneum (unless there is a history of recent abdominal surgery) should raise suspicion for septic peritonitis. Hints for finding the peritoneal gas will be presented. Focal peritonitis is a diagnostic challenge. Unless pancreatitis is severe, the radiographic diagnosis of pancreatitis can be extremely challenging. Most cases of pancreatitis present with normal abdominal radiographs.

5) GI Contrast Studies: The upper GI series is certainly not a common a diagnostic modality since the advent of abdominal ultrasound. I tend to support the use of ultrasound over the tedious process of giving barium. There are however some important indications for using barium or other positive contrast medium in cases of GI disease. Examples of this include: (1.) identification of small mucosal irregularities and ulcers (2.) confirming partial (and less ideally, complete) obstructions. The GI series should never be used to confirm the suspicion of a bowel rupture. If concerns for rupture exist, the patient needs surgery, NOT contrast, regardless of the contrast medium used! Most acute abdomens do not require GI contrast medium. The GI series pulls manpower away from the emergency room. Diagnoses requiring immediate attention can be made from survey radiographs or a focused ultrasound examination.