How to interpret a Contrast-Enhanced Computed Tomography (CECT) of the abdomen?

How to Interpret a Contrast-Enhanced CT (CECT) of the Abdomen

A systematic approach to reading CECT abdomen includes evaluating the scout view, using both 2D and 3D visualization techniques, and methodically assessing all abdominal organs with particular attention to specific CT signs of pathology.

Initial Assessment

• Always begin by reviewing the CT scout view, which can provide complementary information and reveal findings outside the scanned field of view, such as unsuspected lung cancer at the lung bases 1, 2
• Confirm adequate bowel preparation and insufflation if applicable, as inadequate preparation can lead to misinterpretation 3
• Check technical parameters including slice thickness (ideally 3mm for optimal spatial resolution) and contrast administration protocol 3

Systematic Approach to Reading

Step 1: Review 2D and 3D Images

• Use both primary 2D and 3D visualization techniques for optimal detection of pathology 3
• For 2D review, examine enlarged images sequentially from rectum to cecum 3
• For 3D review, evaluate the endoluminal surface of organs for better visualization of lesions 3
• Compare supine and prone datasets when available to differentiate fixed lesions from mobile contents 3

Step 2: Evaluate Specific Organs

Liver

• Assess for focal lesions, noting enhancement patterns during arterial, portal venous, and delayed phases 3
• For indeterminate lesions >1cm, multiphase contrast-enhanced CT has 91-95% accuracy for hemangiomas and 85-93% accuracy for focal nodular hyperplasia 3
• Look for signs of cirrhosis, portal hypertension, or biliary dilation 3

Appendix

• Normal appendix: diameter <6mm, no wall thickening, no surrounding inflammation 3
• Signs of appendicitis: maximal outer diameter >6-8mm, fat stranding, absence of intraluminal gas 3
• Optimal cutoff for maximum outer diameter is 8.2mm (sensitivity 88.8%, specificity 93.4%) 3
• Signs of perforation: extraluminal gas (OR 28.9), intraluminal fecalith (OR 5.7), and wall thickness >3mm (OR 3.2) 3

Pancreas, Spleen, Kidneys, and Adrenals

• Evaluate for size, contour abnormalities, and enhancement patterns 3
• For pancreas, look for parenchymal abnormalities, ductal dilation, or peripancreatic fluid 3
• For kidneys, assess for hydronephrosis, stones, masses, or inflammatory changes 3

Bowel

• Evaluate wall thickness, enhancement pattern, and surrounding fat 3
• Signs of bowel injury: wall thickening, abnormal enhancement, free fluid, pneumoperitoneum 3
• Flat lesions appear as cigar-shaped, plaque-like focal regions of soft tissue attenuation on 2D images 3

Step 3: Assess Vascular Structures

• Evaluate the aorta, major branches, and portal venous system 3
• Look for aneurysms, dissection, thrombosis, or stenosis 3

Step 4: Review Extracolonic Tissues

• Examine the extracolonic tissues for incidental findings 3
• Evaluate for lymphadenopathy, ascites, or free air 3

Interpretation Pitfalls to Avoid

• Volume averaging can cause misdiagnosis when section thicknesses are larger than lesions; repeat CT with thinner sections may be needed 4
• Inadequate oral contrast administration can cause normal structures to simulate tumors 4
• Position changes of organs due to prior surgery can raise suspicion of masses unless clinical history is known 4
• Avoid overreliance on single CT signs; combine multiple findings for more accurate diagnosis 3
• For appendicitis, presence of two or more signs (diameter >6mm, fat stranding, absence of intraluminal gas) increases odds ratio to 6.8 3

Special Considerations

• For suspected appendicitis, CECT without enteral contrast has sensitivity 90-100% and specificity 94.8-100%, comparable to CECT with enteral contrast 3
• For indeterminate liver lesions, MRI may be necessary for definitive characterization 3
• In trauma patients, CT has a sensitivity of 97% and specificity of 95% for detecting significant intra-abdominal injuries 3
• Small bowel and diaphragmatic injuries are more difficult to diagnose on CT and require careful evaluation 3

By following this systematic approach to interpreting CECT of the abdomen, clinicians can maximize diagnostic accuracy and minimize interpretation errors.