Small bowel obstruction (SBO) has been reported to be present in 2% of all patients presenting to the E.D. with abdominal pain.1 A delay in diagnosis is associated with worsening morbidity and mortality,2 and the vast majority of patients with SBO are first seen in the E.D.3 Bedside imaging methods for the diagnosis of an SBO include abdominal X-ray (AXR) and ultrasound (US). A recent meta-analysis by Taylor et al4 compared those diagnostic modalities and found surprising results. AXR has a paultry +LR of 1.6 and a –LR of 0.43. Ultrasound, however, was found to have a +LR of 14.1 and a –LR of 0.13 when performed in the radiology department, and a +LR of 9.5 and a –LR of 0.04 when performed by emergency physicians.4
When scanning the abdomen, you should use a systematic approach so critical findings are not missed. One such method is called moving the lawn:
The main finding diagnostic of SBO on US is the visualization of dilated loops of bowel >2.5 cm.4
Other findings that increase the likelihood of SBO include thickened bowel walls >3mm5 and hyperechoic material moving back and forth within thickened bowel loops.
Concomitant abdominal free fluid has been demonstrated to be associated with higher grade obstruction.6 The tanga sign7 represents abdominal free fluid between loops of bowel.
Post and Scan by: Jacob Avila, MD, RDMS
Hastings RS, Powers RD. Abdominal pain in the ED: a 35 year retrospective. Am J Emerg Med. 2011; 29:711–6. [pubmed]
Bickell N, Federman A, Aufses AH. Influence of time on risk of bowel resection in complete small bowel obstruction. J Am Coll Surg. 2005; 201:847–54. [pubmed]
Foster NM, McGory ML, Zingmond DS, Ko CY. Small bowel obstruction: a population-based appraisal. J Am Coll Surg. 2006; 203:170–6. [pubmed]
Taylor MR, Lalani N. Adult small bowel obstruction. Acad Emerg Med. 2013;20(6):528-44. [pubmed]
Hefny AF, Corr P, Abu-zidan FM. The role of ultrasound in the management of intestinal obstruction. J Emerg Trauma Shock. 2012;5(1):84-6. [pubmed]
Grassi R, Romano S, D’amario F, et al. The relevance of free fluid between intestinal loops detected by sonography in the clinical assessment of small bowel obstruction in adults. Eur J Radiol. 2004;50(1):5-14. [pubmed]
Mizio, Roberto. Small Bowel Obstruction CT Features with Plain Film and US Correlations. Milan: Springer, 2007. Print. [Amazon]