Madtown Sono

Elderly female with abdominal pain and nausea

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By Arika Wieneke, MD
Edited by Hani I. Kuttab, MD and Leah Anderson, MD

Clinical Case

An elderly female with past medical history of a prior appendectomy and bowel resection presented to the emergency department with abdominal pain for three days. Patient denied vomiting. Initial vital signs notable for blood pressure 128/73, heart rate of 79 beats/minute, respiratory rate of 16 breaths/minute, temperature of 36.8°C (98.2°F), and oxygen saturation of 97% on room air. Abdominal examination revealed diffuse tenderness with intermittent guarding in the lower abdomen. Remainder of the exam was otherwise unremarkable. Point-of-care ultrasound (POCUS) was performed (Figures 1 & 2).

Ultrasound clip
Figure 1: Ultrasound image of bowel demonstrating small bowel obstruction.
Figure 2: Ultrasound clip demonstrating small bowel dilation and abnormal peristalsis.

Diagnosis

Small bowel obstruction (SBO). Ultrasound images of the bowel demonstrated small bowel dilation, measuring at 3.84cm (>2.5 cm is abnormal). Figure 2 also demonstrates a notable transition point, with the proximal end showing abnormal peristalsis and the distal end with dilation and no obvious peristalsis. CT scan of the abdomen and pelvis was performed and showed a high-grade SBO (Figure 3). General surgery was consulted who recommended nasogastric tube placement and admission to their service for a trial of conservative management.

Figure 3: CT scan of the abdomen and pelvis (coronal view) demonstrating small bowel dilation, consistent with obstruction.

Discussion

Point-of-care ultrasound is an excellent tool for the evaluation of patients with abdominal pain. Ultrasound of the bowel can be performed quickly and accurately. One systematic review and meta-analysis demonstrated ultrasound to be 92.4% sensitive and 96.6% specific for diagnosing small bowel obstruction.1

While many studies indicate that CT scan is the best imaging modality for the diagnosis of SBO, ultrasound has been proven to be more sensitive and specific at making this diagnosis as compared to abdominal x-ray.1-3 Ultrasound can easily be incorporated into the general evaluation of patients presenting to the emergency department with abdominal pain and can assist with early identification of SBO. It may also assist in risk-stratifying potential cases to determine who needs intervention faster (e.g., nasogastric tube, surgical consult, or expedited CT imaging).

Ultrasound evaluation of the small bowel is easy to learn. We recommend using the curvilinear probe and assessing the small bowel in a systematic approach. Some recommend evaluation of each quadrant of the abdomen in both the transverse and coronal place (8 total clips). Others utilize the “lawnmower approach,” beginning in the right lower quadrant and scanning across the entire abdomen, upwards and downwards, until you reach the left lower quadrant. You may also hand the probe to the patient and ask them to place the probe on the area in which they feel their pain!

Possible Limitations

  1. Poor visualization in patients with more subcutaneous/adipose tissue or in patients with more bowel gas.
  2. Less accurate with partial SBO compared to complete SBO.
  3. More difficult to locate the transition point on ultrasound compared to CT.
  4. Ultrasound may not show you the etiology or cause of the SBO.

Ultrasound Findings Seen in SBO

  1. Small bowel dilation >2.5 cm
    • Be sure you are measuring small bowel and not large bowel (small bowel has plicae circulares, which stretch all the way across the bowel wall versus the haustra of the colon which do not).
  2. “To-and-fro” motion of bowel contents (i.e., abnormal peristalsis)
    • Also known as the ‘washing machine sign’, the contents within the small bowel will be visualized moving forwards, then being expelled backwards.
  3. Non-Compressible Small Bowel
    • Dilated small bowel will not compress when pressure is applied from the ultrasound probe
  4. “Keyboard sign”
    • As the small bowel fills and dilates, the plicae circulares of the small bowel becomes more prominent and is easily visualized as finger-like projections, resembling piano keys.
  5. Bowel wall edema >4mm and free fluid around the bowel
    • These findings are concerning for ischemia or infarction. If you see either of these, you may consider expediting CT imaging and a surgical consult!

Teaching Points

  1. Ultrasound is a quick and effective way to evaluate for small bowel obstruction.
  2. Most common ultrasound finding in SBO is small bowel dilation >2.5 cm.
  3. Be aware of possible limitations, and still obtain CT scan if deemed appropriate.

References

  1. Gottlieb M, Peksa GD, Pandurangadu AV, Nakitende D, Takhar S, Seethala RR. Utilization of ultrasound for the evaluation of small bowel obstruction: A systematic review and meta-analysis. Am J Emerg Med. 2018 Feb;36(2):234-242. doi: 10.1016/j.ajem.2017.07.085. Epub 2017 Jul 29. PMID: 28797559.
  2. Barzegari H., Delirooyfard A., Moatamedfar A., Sohani S., Sohani M. A new point of care ultrasound in disposition of patients with small bowel obstruction in emergency department. International Journal of Pharmaceutical Research & Allied Sciences. 2016;5(2):200–207.
  3. Jang TB, Schindler D, Kaji AH. Bedside ultrasonography for the detection of small bowel obstruction in the emergency department. Emerg Med J. 2011 Aug;28(8):676-8. doi: 10.1136/emj.2010.095729. Epub 2010 Aug 22. PMID: 20732861.
  4. Pourmand A, Dimbil U, Drake A, Shokoohi H. The Accuracy of Point-of-Care Ultrasound in Detecting Small Bowel Obstruction in Emergency Department. Emerg Med Int. 2018;2018:3684081. Published 2018 Apr 4. doi:10.1155/2018/3684081.