Why Perform Triphasic CT for Cirrhosis
Triphasic CT is performed in cirrhotic patients primarily to detect and diagnose hepatocellular carcinoma (HCC) without biopsy, leveraging the characteristic arterial enhancement and delayed washout pattern that defines HCC on imaging. 1
Primary Indication: HCC Detection and Diagnosis
The fundamental reason for triphasic CT in cirrhosis is that it can establish a definitive HCC diagnosis without requiring biopsy when characteristic enhancement patterns are present. 1 This is critical because:
- Cirrhotic patients have a 1.5% annual risk of developing HCC, making surveillance cost-effective 2
- For nodules >2 cm showing arterial phase hyperenhancement (APHE) with washout on portal/delayed phases, a single triphasic CT showing typical hallmarks establishes "definite" HCC diagnosis without biopsy 1
- Biopsy carries 1-3% risk of needle tract seeding and should be avoided when imaging is diagnostic 2
The Three Phases Explained
The triphasic protocol captures distinct vascular phases that reveal HCC's unique blood supply:
Arterial Phase (22-30 seconds post-contrast):
- HCC demonstrates arterial-dominant vascularity with brisk enhancement 3
- Detects 58% of small HCCs that show hyperenhancement 4
- Critical for identifying lesions that may be isoattenuating in other phases 4
Portal Venous Phase (49-73 seconds post-contrast):
- Most HCCs become hypoattenuating relative to liver parenchyma 4
- Provides anatomic detail for surgical planning 3
Delayed Phase (5-10 minutes post-contrast):
- 90% of HCCs show hypoattenuation (washout) 4
- Adding delayed phase increases sensitivity from 86.8% (dual-phase) to 93.8% (triphasic) for detecting small (≤2 cm) HCCs 4
- The delayed phase is particularly valuable because it captures washout that may not be evident on portal venous imaging alone 4
Diagnostic Performance
For HCC of any size in cirrhosis, triphasic CT achieves 77.5% sensitivity and 91.3% specificity 5, though this means:
For resectable HCC specifically, sensitivity drops to 71.4% with 92% specificity 5, meaning 28.6% of resectable tumors would be improperly excluded from surgery 5.
When Triphasic CT is Recommended Over Ultrasound
The ACR Appropriateness Criteria specify triphasic CT (rated 7-8/9) should replace ultrasound surveillance when: 2
- Obesity limits ultrasound visualization 2, 6
- Nodular cirrhotic liver obscures lesions on ultrasound 2
- Nonalcoholic fatty liver disease (NAFLD) impairs ultrasound sensitivity 2, 6
- Patient is at very high risk for HCC (e.g., on transplant waiting list) 2
- Indeterminate lesions are detected on screening ultrasound 2
Size-Based Diagnostic Algorithm
For nodules <1 cm: Follow with ultrasound every 3-6 months; triphasic CT not yet indicated 1, 6
For nodules 1-2 cm: Requires at least two dynamic imaging studies (triphasic CT, MRI, or contrast ultrasound) showing characteristic features for non-invasive diagnosis 1, 6
For nodules >2 cm: Single triphasic CT showing APHE with washout is sufficient for definitive HCC diagnosis without biopsy 1, 6
Critical Limitations and Pitfalls
Triphasic CT has significant limitations for diagnosing cirrhosis itself:
- Low sensitivity for detecting cirrhosis and noncirrhotic fibrosis even when assessing multiple morphologic features 7
- Noncontrast CT only shows structural changes in very advanced disease 7
- For fibrosis staging, MR elastography is superior to CT 7
For HCC detection specifically:
- CT underestimates tumor burden by 25-30% even with optimal technique, particularly for lesions <2 cm 1
- Sensitivity is size-dependent: 61-73% for lesions >2 cm, 44-65% for 1-2 cm lesions, and only 10-43% for lesions <1 cm 1
- Fibrous septa and regenerative nodules in cirrhotic livers can mask small tumors 7
Comparison to Alternative Modalities
MRI advantages over triphasic CT:
- Better sensitivity and specificity in nodular cirrhotic livers 1
- No ionizing radiation exposure 2
- Gadoxetate-enhanced MRI provides superior parenchymal enhancement in cirrhosis 2
However, triphasic CT remains appropriate when: