What is the difference between CT (Computed Tomography) enterography and CT enterography with angiography in diagnosing small bowel bleeding or inflammation?

Difference Between CT Enterography and CT Enterography with Angiography

CT enterography with angiography provides multiphasic imaging that better detects active bleeding and vascular lesions compared to standard CT enterography, which primarily evaluates bowel wall inflammation and structural abnormalities.

CT Enterography: Basic Features

• CT enterography (CTE) is designed specifically to optimize evaluation of the small bowel wall and requires ingestion of approximately 1.5L of neutral oral contrast material over one hour to achieve adequate bowel distention 1
• Standard CTE typically involves a single imaging phase acquired during the enteric or portal venous phase (50-70 seconds after contrast injection), which is adequate for detecting inflammation and most masses 1
• Neutral oral contrast agents (with attenuation values near water) are preferred as they allow hyperenhancing pathologies to appear more conspicuous against the hypointense background 1
• CTE is particularly useful for evaluating inflammatory conditions such as Crohn's disease, radiation enteritis, NSAID enteropathy, and most small bowel malignancies 1

CT Enterography with Angiography: Enhanced Capabilities

• CT enterography with angiography (multiphase CTE) adds arterial phase imaging and sometimes delayed phase imaging to the standard protocol 1
• The arterial phase is acquired earlier in the contrast bolus (typically 25-35 seconds after injection) to visualize active extravasation and vascular lesions 1
• Some protocols also include a delayed phase (90 seconds after injection) to detect slowly bleeding lesions 1
• Multiphase CTE should include at least arterial and enteric/portal venous phases, with unenhanced images (conventional or virtual noncontrast) acquired in all cases 1
• No oral contrast should be administered for pure CT angiography (CTA), as this could dilute or obscure active extravasation 1

Clinical Applications and Indications

• Standard CTE is indicated for:

  • Evaluation of inflammatory bowel disease (especially Crohn's disease) 1
  • Assessment of small bowel tumors 1
  • Evaluation of NSAID-induced enteropathy 1

• CT enterography with angiography (multiphase CTE) is indicated for:

  • Patients over 40 years of age with suspected small bowel bleeding, as vascular lesions are more common in this population 1
  • Evaluation of suspected small bowel bleeding sources after negative endoscopy 1, 2
  • Detection and characterization of vascular lesions such as angioectasias and Dieulafoy lesions 1, 3

Diagnostic Yield and Performance

• Multiphase CTE has higher diagnostic yield for detecting vascular lesions, with certain pathologies being more visible in specific phases:

  • Dieulafoy lesions are most conspicuous on arterial phase 1, 3
  • Small neuroendocrine tumors are best seen on enteric phase 1
  • Slowly bleeding angioectasias may only be visible on delayed phase 1

• The overall diagnostic yield of multiphase CTE for suspected small bowel bleeding is approximately 31.6%, with higher yield for overt bleeding (35.0%) compared to occult bleeding with only iron-deficiency anemia (26.1%) 2

• Multiphase CTE has excellent sensitivity (90.2%) and positive predictive value (98.2%) for small bowel masses 2

Technical Considerations and Pitfalls

• The most common technical pitfall of CTE is inadequate small bowel distention, which can result from inadequate ingestion, gastric retention, or rapid transit of enteric contrast 4
• For pure CTA in acute bleeding, no oral contrast should be administered as it can dilute or mask active extravasation 1
• Jejunal segments are frequently collapsed in CTE, which can lead to false interpretations 4
• Interpretive pitfalls commonly result from peristaltic contractions, transient intussusception, and opaque intraluminal debris 4

When to Choose Which Technique

• Standard CTE should be used for:

  • Evaluation of inflammatory conditions like Crohn's disease 1
  • Assessment of non-bleeding related small bowel pathology 1
  • Patients under 40 years where inflammatory conditions are more likely than vascular lesions 1

• CT enterography with angiography (multiphase CTE) should be used for:

  • Suspected small bowel bleeding in hemodynamically stable patients 1
  • Patients over 40 years with suspected small bowel bleeding 1
  • Cases where vascular lesions are suspected 1

• Pure CTA (without enterography protocol) should be used for:

  • Hemodynamically unstable patients with active bleeding 1
  • First-line study when suspicion of active bleeding is high 1

Radiation Considerations

• Both techniques involve radiation exposure, but multiphase CTE involves additional radiation due to the multiple acquisitions 1, 4
• The benefit of improved diagnostic yield must be weighed against the increased radiation exposure, particularly in younger patients 1, 4