Ultrasound for Small Bowel Obstruction

By Jordan Valentin, DO, MSEmergency Medicine PGY-3

Clinical scenario

A 68-year-old man with hypertension, hyperlipidemia, prior appendectomy, small bowel resection, and recurrent small bowel obstructions presents with 2 days of worsening abdominal pain, nausea, vomiting, and distension. His last bowel movement was yesterday, and he has not passed flatus since. He says it feels like his previous obstructions.

• Vitals: BP 128/74, HR 104, RR 18, T 37.1 °C

• Exam: distended, tympanitic abdomen with diffuse tenderness, worst around the umbilicus. No guarding, rebound, or rigidity.

You grab the ultrasound. What are you looking for? Small bowel obstruction (SBO).

How to scan for SBO

• Probe: curvilinear.

• Technique: start in the right lower quadrant and sweep systematically across the abdomen in a "lawnmower" pattern.

• Image abnormal bowel in both transverse and longitudinal views.

• Evaluate multiple loops for:

  • diameter

  • peristalsis

  • bowel-wall appearance

  • free fluid

What does normal small bowel look like?

• Relatively small caliber

• Active, coordinated peristalsis

• Normal bowel-wall layers

• Plicae circulares traversing the lumen

This patient's ultrasound

The images (Figures 1–4 and the linked PDF) show multiple dilated, fluid-filled small bowel loops with prominent plicae circulares, producing the characteristic "keyboard" or "piano key" appearance. There is also anechoic free fluid between the dilated loops, forming the triangular "tanga" sign.

Figure 1. SBO on POCUS: dilated bowel, to-and-fro peristalsis, and valvulae conniventes (plicae circulares).

Figure 2. Dilated, fluid-filled small bowel.

Figure 3. Small bowel obstruction on ultrasound.

Figure 4. Small bowel obstruction on ultrasound.

Classic POCUS findings in SBO

Finding	What you see
Dilated bowel	Small bowel > 2.5 cm in diameter is abnormal
Keyboard/piano-key sign	Prominent plicae circulares visible in dilated, fluid-filled bowel
To-and-fro sign	Contents shuttle back and forth instead of moving forward, because they cannot pass the obstruction
Tanga sign	Triangular (thong-shaped) free fluid between dilated loops

Figure 5. Dilated bowel loop > 2.5 cm with plicae circulares (“keyboard sign”).

Management

• NPO

• IV fluids

• Analgesia

• Antiemetics

• Nasogastric decompression

• General surgery consultation

Clinical pearls

• Dilated (> 2.5 cm) fluid-filled loops plus to-and-fro peristalsis at the bedside: think SBO and call surgery early.

• POCUS can speed the diagnosis while you arrange definitive imaging and decompression.

Resource

• Ultrasound Education of the Week: SBO (Word document, with ultrasound images)

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