From the Guidelines
Signs of small bowel obstruction on abdominal X-ray include dilated small bowel loops greater than 3 cm in diameter with visible valvulae conniventes, multiple air-fluid levels in an upright film, and a paucity of gas in the large bowel and rectum. These radiographic findings reflect the pathophysiology of obstruction where intestinal contents accumulate proximal to the blockage, causing distension and increased intraluminal pressure, while the bowel distal to the obstruction collapses as it empties 1. The classic "stepladder" pattern may be visible, showing progressively dilated loops of small bowel at different levels. A transition point between dilated and collapsed bowel segments might be identified, indicating the location of obstruction. Other supportive findings include the "string of pearls" sign (small bubbles of gas trapped between fluid and valvulae conniventes) and thickened bowel walls.
Some key points to consider when interpreting abdominal X-rays for small bowel obstruction include:
- Dilated small bowel loops greater than 3 cm in diameter with visible valvulae conniventes
- Multiple air-fluid levels in an upright film
- Paucity of gas in the large bowel and rectum
- The "stepladder" pattern, showing progressively dilated loops of small bowel at different levels
- A transition point between dilated and collapsed bowel segments, indicating the location of obstruction
- The "string of pearls" sign and thickened bowel walls as supportive findings
However, abdominal X-rays have limited sensitivity (around 60-70%) for small bowel obstruction, so a normal X-ray does not exclude the diagnosis if clinical suspicion remains high 1. In such cases, further imaging with CT or other modalities may be necessary to confirm the diagnosis and guide management.
In terms of management, CT abdomen and pelvis with IV contrast is usually appropriate for the initial imaging of a suspected small bowel obstruction with an acute presentation 1. The use of abdominal radiographs is controversial, but may be appropriate as an initial imaging examination to direct further workup, which would usually include a CT of the abdomen and pelvis with IV contrast.
It's also important to note that computed tomography has a higher sensitivity and specificity than conventional abdominal radiography and ultrasound, and can provide information about the underlying cause of obstruction or alternative diagnoses 1.
Overall, while abdominal X-rays can provide some useful information in the diagnosis of small bowel obstruction, they should be used in conjunction with other imaging modalities and clinical findings to guide management.
From the Research
Radiographic Signs of Small Bowel Obstruction
The radiographic signs of small bowel obstruction on abdominal X-ray include:
- Air-fluid levels of differential height in the same small-bowel loop 2
- A mean air-fluid level width greater than or equal to 25 mm on upright abdominal radiographs 2 These findings are strongly associated with the severity of obstruction and can be used to distinguish complete or high-grade partial small-bowel obstruction from low-grade partial or no small-bowel obstruction 2.
Importance of Upright Abdominal Radiographs
Upright abdominal radiographs are important in the examination of patients with suspected small-bowel obstruction and may contribute to the imaging triage of these patients 2.
Limitations of Current Evidence
While the current evidence provides some insight into the radiographic signs of small bowel obstruction, it is largely focused on the role of imaging in diagnosis and management, rather than providing a comprehensive list of radiographic signs 3, 4, 5, 6.