Pt is 54 yo M with PMH of DM, HTN, Crohn Disease presents with 2 days of worsening vomiting, had diarrhea initially that has now stopped and is no longer passing gas, also reports some slight abdominal distention. Patient has had several abdominal surgeries in the past, denies any fevers, any blood in the vomit or diarrhea, no travel. An abdominal exam reveals a soft, slightly tympanic, diffuse moderate tenderness. Pt is afebrile and normotensive. You have a strong suspicion for a small bowel obstruction and place the order to put the patient for CT, however, there’s been difficulty getting people to CT in a timely fashion all day so your attending suggests getting an abdominal xray to expedite diagnosis. How good is the abdominal xray at diagnosing small bowel obstruction and what other imaging modalities do we have at our disposal?
The abdominal xray for detection of small bowel obstruction has been shown to have sensitivity of 66-77% and specificity of 50-57% [1-3]. Another study also showed that addition of abdominal plain films to acute abdominal pain patients did not significantly change management . The other main idea is that you will be sparing the patient radiation but with such poor sensitivity/specificity, it’s been shown not to significantly spare the patient further imaging . The other criticism of plain radiography is that it relies heavily on the presence of air-fluid levels to be present in order to diagnosis SBO, however, air is not always present in every small bowel obstruction.
There has been emerging evidence that abdominal ultrasound is shown to be superior to abdominal xray in detecting small bowel obstruction . Ultrasound being reported when seeing dilated bowel to have a sensitivity of 91% and a specificity of 84% . The common accepted cutoff for dilated small bowel is >2.5 mm, also looking for a “piano sign” or “keyboard sign” representing the plicae circularis of the small bowel.
Ultrasound offers the advantage of no radiation, bedside evaluation and does not rely on presence of air (air-fluid levels) of plain radiography.
There is a great podcast on the subject by Sono Gurus Mike and Matt that I encourage those interested to check out.
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2. van Randen A, Laméris W, Luitse JS, Gorzeman M, OPTIMA study group. The role of plain radiographs in patients with acute abdominal pain at the ED. Am J Emerg Med. 2011 Jul;29(6):582-589.e2. doi: 10.1016/j.ajem.2009.12.020. Epub 2010 Apr 24. PubMed PMID: 20825832.
3. Maglinte DD, Reyes BL, Harmon BH, Kelvin FM. Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR Am J Roentgenol. 1996 Dec;167(6):1451-5. PubMed PMID: 8956576
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