CT Scan Protocol for Liver Cyst Evaluation
For a patient with a liver cyst, order a multiphase contrast-enhanced CT of the abdomen with intravenous contrast, including arterial and portal venous phases at minimum (triple-phase with delayed phase is preferred). 1
Rationale for Multiphase Contrast CT
The primary goal is to differentiate a simple benign cyst from cystic neoplasms, infected cysts, or other pathology that would require intervention. Multiphase contrast-enhanced CT correctly differentiates malignant from benign lesions in 74-95% of cases, which is critical for determining whether the cyst requires treatment or surveillance. 2
Technical Specifications
- Triple-phase protocol should include arterial phase (8 seconds after trigger threshold of 100 HU in lower thoracic aorta), portal venous phase (23 seconds), and delayed phase (48 seconds) for optimal lesion characterization 1, 3
- Use 2.5-5 mm slice thickness for optimal lesion characterization 4
- Administer 1.5 mL/kg of contrast at 3.0 mL/s using a pressure injector 3
When to Consider Alternative Imaging
If the cyst appears atypical on initial imaging (irregular walls, septations, calcifications, or daughter cysts), MRI with and without IV contrast is superior to CT, establishing a definitive diagnosis in 95% of liver lesions versus only 90% with CT. 2, 5
MRI Advantages Over CT
- Gadoxetate-enhanced MRI achieves 95-99% accuracy for characterizing liver lesions and requires further imaging in only 1.5% of cases versus 10% with CT 2
- MRI is particularly valuable when malignancy cannot be excluded or when the patient has chronic liver disease 1
Clinical Context Matters
Normal Liver, No Known Malignancy
- Simple hepatic cysts occur in up to 15% of the general population and are typically benign 2
- Multiphase contrast-enhanced CT, MRI with contrast, or contrast-enhanced ultrasound (CEUS) are equivalent first-line options for lesions >1 cm 2, 4
Known Extrahepatic Malignancy
- Metastatic disease must be excluded, though benign lesions still occur in nearly 30% of cancer patients 2
- Consider adding FDG-PET/CT when the lesion was initially found on noncontrast imaging 4
Chronic Liver Disease/Cirrhosis
- Use Liver Imaging Reporting and Data System (LI-RADS) protocol with triple-phase contrast CT (arterial, portal venous, delayed) as the preferred option 4
- For lesions ≥10 mm in cirrhotic patients, hepatocellular carcinoma becomes the primary concern 2, 4
Common Pitfalls to Avoid
- Single-phase CT is inadequate for proper characterization of liver lesions; multiphasic imaging is essential 6
- Do not order CT without contrast for cyst evaluation—it has a rating of only 3 (usually not appropriate) by ACR guidelines 1
- Cysts with irregular walls, septations, calcifications, or daughter cysts require enhanced CT or MRI to differentiate simple cysts from cystic neoplasms or hydatid cysts 5
- Tc-99m sulfur colloid scans have no role in modern evaluation of liver lesions 4
When Biopsy Is Needed
- Refer to interventional radiology for percutaneous image-guided biopsy only when imaging features indicate possible malignancy or when histopathologic diagnosis is required 2, 6
- Avoid biopsy of solid benign liver lesions such as hemangiomas by obtaining diagnostic CT or MRI first 2
- Be aware that postbiopsy bleeding risk is 9-12%, particularly with hypervascular lesions 2