What type of CT should I order if I am concerned about a gastrointestinal perforation?

CT Imaging for Suspected Gastrointestinal Perforation

Order a CT abdomen and pelvis WITH intravenous (IV) contrast, without oral contrast. 1, 2

Imaging Protocol Specifications

The optimal CT protocol includes:

• IV contrast is essential to assess for bowel wall enhancement, focal wall defects, mucosal interruption, and inflammatory changes that significantly improve diagnostic accuracy 1
• Oral contrast should NOT be used (or use neutral oral contrast like water) because positive oral contrast impedes assessment of mucosal enhancement and can obscure intraluminal bleeding 1
• Include both abdomen and pelvis to capture the entire gastrointestinal tract 1

Diagnostic Performance

CT with IV contrast achieves:

• 93-96% sensitivity and 93-100% specificity for detecting perforation 1, 2
• 95% sensitivity and 90-94% specificity for identifying the exact perforation site 1, 2
• 66-87% sensitivity for determining the underlying cause 1

Key CT Findings to Identify

The radiologist will look for:

• Extraluminal gas (present in 97% of perforations) 1
• Focal wall defect or ulcer (84% of cases, positive likelihood ratio of 36.83) 1
• Bowel wall thickening (72% of cases, positive likelihood ratio of 10.52) 1
• Fluid or fat stranding along the gastroduodenal region (89%) 1
• Ascites (89%) 1

The combination of wall defect/ulcer plus wall thickening shows 95% sensitivity and 93% specificity for localizing the perforation site 1

Alternative Imaging When CT Unavailable

If CT is not immediately available in a stable patient:

• Plain X-ray (upright chest/abdomen) can detect free air with 92% positive predictive value but has only 74-84% sensitivity 1, 2
• Ultrasound has 88% sensitivity for detecting fluid but very limited ability to identify the perforation site or cause 1, 2
• Water-soluble contrast enema is a valid alternative for identifying obstruction site but less useful for acute perforation 1

Critical Clinical Caveats

Do NOT delay surgery for imaging if:

• The patient has clear signs of diffuse peritonitis with hemodynamic instability 1
• Physical examination shows obvious peritoneal signs requiring immediate surgical exploration 1

In unstable patients, proceed directly to the operating room - imaging should never expose patients to unsafe treatment delays 1

Special Populations

For pregnant women and children where radiation is a concern:

• Ultrasound may be used as initial screening 2, 3
• However, CT should still be performed if ultrasound is non-diagnostic or the patient is clinically unstable 2