What is the importance of CT (Computed Tomography) enterography?

CT Enterography: Clinical Importance

CT enterography is a critical first-line imaging modality for diagnosing and managing small bowel disorders, particularly Crohn's disease, with excellent diagnostic performance (75-90% sensitivity, >90% specificity) and the unique ability to visualize both mucosal inflammation and transmural/extraenteric complications that endoscopy cannot detect. 1

Primary Diagnostic Capabilities

Superior Small Bowel Visualization

• CT enterography visualizes intramural or proximal small bowel inflammation in approximately 50% of Crohn's disease patients who have endoscopically normal examinations, making it complementary and essential to colonoscopy 1
• The technique allows evaluation of disease proximal to the terminal ileum, beyond the reach of colonoscopes, while detecting transmural disease with overlying normal mucosa that appears normal on direct optical inspection 1
• It provides comprehensive assessment of the entire small bowel wall thickness and depicts extraenteric involvement, offering more detailed information about disease extent and severity than endoscopy alone 2

Detection of Active Inflammation

• Acute inflammation is diagnosed through visualization of thickened small bowel with mural stratification, engorged vasa recti/vasculature, and surrounding inflammatory stranding 1
• The use of neutral oral contrast agents in large volumes (1300-1800 cc) allows evaluation of mucosal enhancement by detecting subtle inflammation that is obscured with positive contrast agents 1
• Mural hyperenhancement combined with IV contrast administration maximizes detection of inflammatory changes related to Crohn's disease 1, 3

Critical Role in Crohn's Disease Management

Initial Diagnosis

• The combination of CT enterography and ileocolonoscopy is advocated as the diagnostic algorithm of choice at initial presentation in United States medical centers 1
• CT enterography establishes Crohn's disease diagnosis when the terminal ileum and colon are not involved or when intramural disease is predominant, which may not be apparent at endoscopy 1
• The cross-sectional nature allows potential diagnosis of entities mimicking Crohn's disease presentation, adding diagnostic utility 1

Complication Detection

• CT enterography excels at detecting complications including obstruction, abscess, and fistula—critical findings that impact morbidity and mortality 1
• The modality's intrinsic high spatial resolution and reproducible quality make it one of the main imaging methods for initial diagnosis of small-bowel Crohn's disease 1
• It can assess for alternative diagnoses and possible complications simultaneously during a single examination 1

Therapeutic Monitoring

• Recent data suggest CT enterography is useful in determining response to therapy, assessing bowel healing, and monitoring disease progression 1
• The technique can detect wall changes that influence treatment decisions in Crohn's disease patients 1
• Detecting transmural healing and complications early improves long-term outcomes compared to relying on clinical symptoms alone 1

Broader Clinical Applications

Small Bowel Bleeding

• CT enterography with angiography is indicated for suspected small bowel bleeding sources after negative endoscopy, with a diagnostic yield of approximately 31.6% 4
• The American College of Radiology recommends this approach for patients over 40 years with suspected small bowel bleeding, as vascular lesions are more common in this population 4
• Multiphase CT enterography has higher diagnostic yield for detecting vascular lesions like angioectasias and Dieulafoy lesions 4

Neoplastic Disease

• CT enterography is recommended for assessment of small bowel tumors with high sensitivity and positive predictive value 4
• The technique has become an important alternative to traditional fluoroscopy in evaluating small bowel neoplasms 3

Other Indications

• CT enterography is recommended for evaluation of NSAID-induced enteropathy and celiac sprue 4, 3
• It is increasingly used in assessment of small bowel infections, adhesions, and polyps 5

Technical Advantages Over Standard CT

Optimized Protocol

• CT enterography represents a specialized protocol with neutral oral contrast, thin collimation, multiplanar reconstruction, and IV contrast that maximizes small bowel visualization 1
• Standard CT with positive oral contrast obscures subtle mucosal enhancement and performs poorly compared to CT enterography for detecting mild inflammation 1
• Optimal bowel distention is critical—without it, peristalsis or collapse can obscure or mimic disease 1

Performance Superiority

• When patients can tolerate oral contrast requirements, CT enterography detects more subtle findings of Crohn's disease compared to standard CT 1
• The technique has become the first-line modality for imaging suspected inflammatory bowel disease, surpassing traditional fluoroscopy 5
• CT enterography provides excellent visualization that traditional small bowel follow-through and plain radiographs cannot achieve 6

Clinical Decision-Making Algorithm

When to Choose CT Enterography

• For indolent presentations where patients can tolerate large volumes of oral contrast (1300-1800 cc over 30-60 minutes), CT enterography is preferred 1
• Use CT enterography for initial diagnosis of suspected Crohn's disease in combination with ileocolonoscopy 1
• Select CT enterography for therapeutic monitoring and assessment of disease distribution 1

When Standard CT May Be Preferred

• In acute presentations where patients are severely ill and unable to tolerate large volume requirements, standard CT (with IV contrast) may be the preferred choice 1
• Presumably, any Crohn's disease findings would not be subtle in severely acute situations 1
• Standard CT remains useful when immediate assessment for complications like perforation or abscess is needed 1

Important Limitations and Pitfalls

Technical Limitations

• The most common technical pitfall is inadequate small bowel distention resulting from inadequate ingestion, gastric retention, or rapid transit of enteral contrast 7
• CT enterography cannot demonstrate isolated mucosal abnormalities such as aphthous ulcers 7
• Segments of jejunum are frequently collapsed even with adequate technique 7

Interpretive Challenges

• Peristaltic contractions, transient intussusception, and opaque intraluminal debris commonly cause interpretive pitfalls 7
• Distinguishing between active disease and fibrosis in strictures remains difficult based on enhancement characteristics alone, though CT enterography performs better than standard CT for this distinction 1, 2

Radiation Considerations

• CT enterography uses ionizing radiation, which is a limitation for repeated examinations over time 1, 7
• MR enterography is preferred for younger patients and long-term monitoring to reduce cumulative radiation exposure 6

Complementary Role with Other Modalities

• CT enterography complements ileocolonoscopy by visualizing areas beyond endoscopic reach and detecting transmural disease 1
• When CT enterography findings are equivocal or suggest significant pathology, further imaging or endoscopy may be needed 6
• Capsule endoscopy and balloon-assisted endoscopy serve as complementary examinations when CT enterography is non-diagnostic 7