Small Bowel Feces Sign
The small bowel feces sign is a CT finding characterized by particulate, mottled, feces-like material mixed with gas bubbles within dilated small bowel loops, most commonly seen in the ileum, and serves as a specific indicator of small bowel obstruction that helps localize the transition point. 1, 2, 3
Radiologic Appearance
The sign consists of the following CT characteristics:
- Gas bubbles mixed with particulate matter resembling colonic feces within dilated segments of small bowel 3
- Mottled, feces-like content within the lumen of dilated loops proximal to the obstruction 1
- The particulate material can be traced to the point of transition and is most conspicuous at the transition zone 2
- Length of fecal-like material ranges from 2 to 25 cm, with longer segments seen in moderate and high-grade obstruction 2
Clinical Significance and Prevalence
The sign has important diagnostic implications but variable frequency:
- Present in 55.9% of patients with confirmed small bowel obstruction in prospective studies 2
- More commonly identified in moderate (72.7%) and high-grade (58.8%) obstruction compared to mild obstruction (16.6%) 2
- Predominantly localizes to ileal loops in the vast majority of cases 1, 4
- Indicates subacute or progressive obstruction rather than acute strangulation in most cases 1, 4
Diagnostic Utility
When present on CT, the small bowel feces sign reliably helps locate the transition zone in patients with small bowel obstruction 5, 2. The ACR Appropriateness Criteria notes that the absence of small-bowel feces suggests early surgical intervention should be considered 5.
Important Caveat - Specificity Concerns
A critical pitfall exists that must be recognized:
- The sign can appear in 6% of patients presenting with acute abdominal/flank pain WITHOUT bowel obstruction 6
- When associated with normal or mildly dilated small bowel (<3 cm), the majority of patients (100% in one study) have no obstruction 6
- The sign becomes highly specific for obstruction only when combined with moderate-to-severe small bowel dilatation (≥3 cm) and distal collapse 6
- This combination (feces sign + moderate/severe dilatation + distal collapse) was present in 71.9% of obstructed patients but 0% of non-obstructed patients 6
Mechanism
The sign results from intraluminal stagnation of enteric material proximal to the point of obstruction, allowing bacterial fermentation and gas production to create the characteristic feces-like appearance 1, 4.
Clinical Context
While relatively uncommon (7-8% prevalence in obstruction series), the sign is rather specific when properly interpreted and serves as a valuable accessory diagnostic feature 1, 4. However, do not rely on this sign alone—always correlate with the degree of small bowel dilatation and presence of distal collapse to avoid false-positive interpretations in non-obstructed patients 6.