Ultrasound Case of the Month: SBO
To and fro? think SBO!
This is an 83-year old woman with a history of prior abdominal surgeries presenting to the ED as a transfer from her SNF with increasing abdominal distention. Patient has not had a bowel movement in four days although endorses passing occasional flatus. She denies emesis though endorses nausea, hiccupping, and burping. She denies any abdominal pain, fevers, chills, dysuria or urinary frequency.
Diagnosis:
Image was acquired with the curvilinear probe, but any high penetration probe (eg curvilinear of phased array probe) can also be used. Multiple regions of the abdomen should be interrogated when evaluating for SBO.
What are we looking for with abdominal US for SBO?
When evaluating for an SBO, we are looking for fluid filled small bowel loops >2.5-3cm in width. You maybe more likely to see an increase in intestinal contents (fluid and echogenic materials) and you may see to-and-fro or whirling of the intestinal contents. In more severe cases, you may see bowel wall thickening (greater than 3mm) and free fluid which is extraluminal. pSBO may be more difficult to evaluate with the US machine.
What do we see in this video?
Dilated loops of bowel > 2.5cm measured outer wall to outer wall (most sensitive and specific finding).
Bidirectional flow of bowel contents (to and fro or whirling)
Visualization of plicae circularis (“keyboard sign”)
How good is U/S for Detecting SBO?
Ultrasound is superior to abdominal plain films and approaches the sensitivity and specificity of CT scan in many cases.
| Sensitvity | Specificity | |
|---|---|---|
| Abdominal Films | 66-77% | 50-57% |
| CT | 92% | 93% |
| Ultrasound | 88% | 96% |
Author: Dr. Samuel Goldman
Faculty Reviewer: Dr. Kristin Dwyer
References
(Mallo RD, et al. Computed tomography diagnosis of ischemia and complete obstruction in small bowel obstruction: a systematic review. Journal Gastrointestinal Surgery. 2005. May-Jun;9(5):690-4.)
(Ogtata M, et al. Prospective Evaluation of Abdominal Sonography for the Diagnosis of Small Bowel Obstruction. Annals of Surgery. 1996. 23(3):237-241.)
Additional resources:
Podcast on US of SBO from www.ultrasoundpodcast.com: Episode 36 - Small Bowel Obstruction - Ultrasound Podcast
Great view of Plicae Circularis (“Keyboard Sign”) from Emory University