Ultrasound Case of the Month

Video by Victoria Fox; Text by Nichole Michaeli

The Case

51 year old male who presents post-op day 4 after an abdominal surgery with vomiting and abdominal pain and distention. Patient does not endorse fevers or chills, and denies bowel movements or flatus in past day.

Vital signs: BP 144/81 HR 83 Temp 98.2 RR 16 O2 95%

Pertinent physical exam findings:

Alert and oriented x3. Comfortable, no pallor.

Abdomen is distended, tympanic, tender to palpation. Surgical wounds in the LLQ and superior to the umbilicus are intact. Wound to the R abdomen is open with clear drainage.

Catheter in place with clear urine.

A bedside abdominal ultrasound is performed.

What is the diagnosis?

Small bowel obstruction

In the United States, post-operative adhesions from prior abdominal surgery are the most common risk factor for mechanical bowel obstruction. One systematic review found a 9% incidence of small bowel obstruction by any cause after abdominal surgery. Other risk factors include pelvic surgery, abdominal wall or groin hernia, intestinal inflammation, history of neoplasm, prior irradiation and history of foreign body ingestion.

Small bowel obstruction leads to bowel dilation proximal to the obstruction. As dilation increases, there is a decrease in perfusion with can cause bowel edema, necrosis or even perforation.

Small bowel obstruction will often present with nausea, vomiting, intermittent cramping abdominal pain, and an inability to pass flatus or stool. Initial diagnosis can be made by abdominal ultrasound, but it is less useful for determine the location or cause of the obstruction. Abdominal CT can aid with identifying the specific site and severity of the obstruction, the cause, and potential complications.

Ultrasound Findings

Using a curvilinear transducer, scan the patient’s abdomen with the marker towards the patient’s right. Move your probe up and down interrogating all 4 quadrants of the abdomen. SBO can be identified by looking for the following signs:

  • “Keyboard Sign”: Identify the pilcae circulares, which span the entire width of the bowel wall. These will appear like black and white piano keys- the keyboard sign  

  • Dilated Fluid Filled Loops: Measure the width of the bowel. Dilation >2.5cm is suggestive of obstruction  

  • To-and-Fro: In the fluid filled bowel, you may be able to see the liquid moving backwards and forwards again and again as the bowel peristalsis, but there is a distal obstruction. 

  • Tanga Sign: Look for free fluid outside the bowel wall

Case Conclusion

The patient had a CT abdomen/pelvis which showed high-grade small bowel obstruction with transition in the distal ileum. A nasogastric tube was placed and the patient was admitted to surgery for management of the small bowel obstruction.   

Image 1: Keyboard Sign

Image 1: Keyboard Sign

Dilated Bowel Loops >2.5cm

Dilated Bowel Loops >2.5cm

Tanga Sign

Tanga Sign

Another example of small bowel obstruction

Faculty Reviewer: Dr. Kristin Dwyer


  1. Bordeianou L, Dante D. UpToDate: Epidemiology, clinical features, and diagnosis of mechanical small bowel obstruction in adults.

  2. ten Broek RP, Issa Y, van Santbrink EJ, et al. Burden of adhesions in abdominal and pelvic surgery: systematic review and met-analysis. BMJ. 2013 Oct; 347:f5588.

  3. Frasure SE, Hildreth AF, Seethala R, Kimberly HH. Accuracy of abdominal ultrasound for the diagnosis of small bowel obstruction in the emergency department. World J Emerg Med. 2018;9(4):267-271.

  4. Unlüer EE, Yavaşi O, Eroğlu O, et al. Ultrasonography by emergency medicine and radiology residents for the diagnosis of small bowel obstruction. Eur J Emerg Med. 2010 Oct;17(5):260-4.

Ultrasound Case of the Month

Case: Submitted by Dr. Sam Goldman

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. 


Small Bowel Obstruction

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%

Faculty Reviewer: Dr. Kristin Dwyer


(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 Episode 36 - Small Bowel Obstruction - Ultrasound Podcast

Great view of Plicae Circularis (“Keyboard Sign”) from Emory University