Characteristic Findings of Hepatic Malignancy on Triphasic CT
The hallmark finding of hepatic malignancy on triphasic CT is arterial phase hyperenhancement followed by washout (hypoattenuation) in the portal venous or delayed phases—this pattern has 72% sensitivity and 81% specificity for malignancy. 1
Primary Enhancement Pattern for Malignancy
The most diagnostically valuable enhancement pattern consists of:
- Arterial phase hyperenhancement with subsequent portal venous phase washout (becoming hypoattenuating relative to surrounding liver) 2, 3
- This pattern is considered the "typical characteristic" for hepatocellular carcinoma (HCC) and is incorporated into major diagnostic guidelines 2
- For HCC specifically, this arterial hypervascularity with washout allows diagnosis without biopsy in cirrhotic patients with lesions ≥2 cm 2
Additional Malignant Enhancement Patterns
Beyond the classic hypervascular-washout pattern, several other triphasic CT findings suggest malignancy:
- Persistent hypoattenuation across all three phases (iso/hypo/hypo or hypo/hypo/hypo patterns) indicates malignancy, particularly hypovascular metastases 4, 5
- Rim enhancement during arterial and portal venous phases is characteristic of cholangiocarcinoma and some metastases 2
- Combining hypervascularity with any hypoattenuation on any phase increases sensitivity for malignancy to 89% 1
Distinguishing Malignant from Benign Lesions
The critical differentiator is the presence of washout—benign hypervascular lesions maintain enhancement or show different patterns:
- Hemangiomas show peripheral nodular enhancement with progressive centripetal fill-in, remaining hyperenhancing through venous and delayed phases (hypo/hyper/hyper or hyper/hyper/hyper patterns) 2, 3, 5
- Focal nodular hyperplasia (FNH) demonstrates intense arterial enhancement becoming isoattenuating in portal venous phase (hyper/iso/iso pattern), without washout 2, 3, 5
- Adenomas may mimic HCC but typically show transient arterial enhancement with rapid washout—difficult to distinguish from malignancy 2
Metastatic Disease Patterns
Metastases display variable enhancement depending on the primary tumor:
- Hypovascular metastases (majority, 85-90%) are best detected on portal venous phase as hypoattenuating lesions 2, 6
- Hypervascular metastases (10-15%, from neuroendocrine, renal cell, thyroid, melanoma) show arterial enhancement with washout, mimicking HCC 2, 6
- Peripheral rim enhancement with central hypoattenuation is common for metastases 2
Optimizing Triphasic CT Technique
The arterial phase is essential for detecting hypervascular malignancies and should not be omitted:
- Arterial phase (20-27 seconds post-injection) detects small hypervascular HCC and metastases that may be invisible on other phases—revealing additional lesions in 21% of patients with hypervascular malignancies 6, 4
- Portal venous phase (45-80 seconds) provides optimal detection of hypovascular metastases 6, 4
- Delayed/equilibrium phase (5-10 minutes) helps characterize washout patterns 4, 5
Quantitative Analysis
Advanced analysis using hepatic artery and portal vein blood supply coefficients can improve specificity:
- Calculating the relative contribution of arterial versus portal venous blood supply to lesion enhancement increases specificity for malignancy from 81% to 97% while maintaining 76% sensitivity 1
- Malignant lesions show increased hepatic artery coefficients compared to background liver 1
Common Pitfalls to Avoid
- Single-phase CT is inadequate—multiphasic imaging is mandatory when malignancy is suspected 7, 3
- Not all arterially enhancing lesions are malignant—FNH and adenomas can mimic HCC, requiring additional imaging (MRI, sulfur colloid scan) or biopsy when atypical features are present 8, 6
- The unenhanced phase adds minimal diagnostic value for detecting malignancy and can be omitted to reduce radiation 6
- In patients with known malignancy, 30% of liver lesions are benign, so correlation with clinical context is essential 7