Can intussusception (a medical condition where a part of the intestine slides into an adjacent part) be missed on ultrasound if it's not actively occurring during the scan?

Can Intussusception Be Missed on Ultrasound if Not Actively Occurring During the Scan?

Yes, intussusception can be missed on ultrasound if it is not actively occurring during the scan, particularly in cases of transient small bowel intussusception that may spontaneously reduce.

Diagnostic Accuracy of Ultrasound for Intussusception

Ultrasound is the diagnostic modality of choice for detecting intussusception with excellent sensitivity and specificity:

• Sensitivity of 97.9% (95% CI, 95%-100%)
• Specificity of 97.8% (95% CI, 97%-99%) 1

However, these high accuracy rates apply primarily to cases where the intussusception is present during the examination.

Transient Intussusception

Transient small bowel intussusception (TSBI) presents a particular diagnostic challenge:

• These intussusceptions can spontaneously reduce and may not be present during imaging 2
• Typically less than 3.5 cm in length with normal wall thickness and vascularity 2
• Often resolve without treatment and may be clinically insignificant 2

Factors Affecting Detection

Several factors can influence whether an intussusception is detected on ultrasound:

1. Timing of the examination:

   • If the intussusception has spontaneously reduced before imaging, it will not be visible
   • Intermittent or transient intussusception may only be present during certain periods

2. Operator experience:

   • Ultrasound is highly operator-dependent
   • The ACR Appropriateness Criteria notes that detection of free fluid on ultrasound varies by operator skill 3

3. Type of intussusception:

   • Ileoileocolic intussusceptions may be more difficult to detect and reduce 4
   • Colocolic types may have different detection rates 4

4. Patient characteristics:

   • Age of patient (older patients may have different success rates in detection) 4
   • Body habitus affecting ultrasound visualization

Clinical Implications and Management

When intussusception is clinically suspected but not visualized on ultrasound:

1. Serial examinations:

   • Consider repeat ultrasound if clinical suspicion remains high
   • Serial clinical examinations are important as signs may develop over time 3

2. Alternative imaging:

   • CT scan may be considered if ultrasound is negative but clinical suspicion remains high
   • CT has higher sensitivity for detecting other causes of abdominal pain 3

3. Risk stratification:

   • Patients can be divided into high-risk and low-risk groups based on clinical symptoms
   • High-risk patients might benefit from immediate barium enema while low-risk patients should have ultrasound first 5

Pitfalls to Avoid

1. False reassurance from a negative scan:

   • A single negative ultrasound does not completely exclude intussusception if it was transient
   • Clinical correlation is essential

2. Misinterpretation of normal findings:

   • Some normal bowel appearances can mimic intussusception
   • False positive diagnoses can occur (specificity of 89-93%) 6, 5

3. Delayed diagnosis:

   • Delayed diagnosis can lead to complications including ischemia and perforation
   • Mortality rates increase significantly when complications occur 7

In summary, while ultrasound is highly accurate for diagnosing intussusception, transient cases that spontaneously reduce between symptom onset and imaging may be missed. Clinical vigilance and potentially repeat imaging are important when symptoms persist despite negative initial ultrasound findings.