Can liver cancer or metastases (mets) be mistaken for fatty infiltrates on computed tomography (CT) scans in patients with risk factors for liver disease or a history of cancer?

Can Liver Cancer or Metastases Be Mistaken for Fatty Infiltrates on CT?

Yes, focal fatty infiltration can mimic metastatic disease or primary liver malignancy on CT imaging, and conversely, metastases can occasionally be confused with fatty infiltration—this is a well-recognized diagnostic pitfall that requires careful attention to specific imaging features and often additional imaging modalities for definitive characterization. 1, 2

Key Distinguishing Features on CT

Characteristics Favoring Focal Fatty Infiltration:

• Non-spherical, geographic shape rather than round/oval masses 2, 3
• Absence of mass effect on vessels or liver contour—this is critical 2, 3
• CT attenuation values close to water (very low density) 2
• No distortion of intrahepatic vessels passing through the area 3

Characteristics Favoring Metastases:

• Round or oval shape with well-defined borders 2
• CT attenuation closer to normal liver parenchyma than water (unless cystic/necrotic) 2
• Mass effect on surrounding structures 1
• Typically hypoattenuating on contrast-enhanced CT 1

Clinical Context That Increases Confusion

Post-chemotherapy patients are particularly problematic because focal fatty infiltration commonly develops after fluorouracil- and irinotecan-based chemotherapy, sometimes distributed throughout the liver in a pattern that can mimic metastases 1. This is especially challenging when evaluating treatment response.

Fatty liver itself reduces CT sensitivity for detecting metastases, making the distinction even more difficult 1.

Recommended Diagnostic Algorithm

Step 1: Optimize CT Technique

If CT is your initial or only modality available:

• Use multiphase contrast-enhanced CT (arterial and portal venous phases) rather than single-phase imaging 4
• Ensure proper contrast bolus timing 4
• Use slice thickness of 2.5-5 mm for adequate lesion detection 4

Step 2: Apply Imaging Criteria

Evaluate for:

• Shape (geographic vs. spherical)
• Mass effect (absent in fatty infiltration)
• Density measurements (water density favors fat)
• Vessel displacement or encasement

Step 3: Problem-Solving with Additional Imaging

If diagnosis remains uncertain after optimized CT, MRI is the definitive next step:

• MRI with IV contrast has 83-98% specificity for differentiating benign from malignant lesions 1
• MRI demonstrates focal high signal intensity on both T1- and T2-weighted images in fatty infiltration, which is diagnostic 5
• MRI establishes definitive diagnosis in 95% of liver lesions 4
• Contrast-enhanced MRI with hepatobiliary agents achieves 94% accuracy for lesion characterization 1

Contrast-enhanced ultrasound (CEUS) is an excellent alternative:

• CEUS correctly characterizes 89% of focal fat areas 1
• CEUS correctly identifies 86-98% of metastases 1
• In noncirrhotic patients, specific washout patterns on CEUS have 97% sensitivity and 100% specificity for malignancy 1

Step 4: When Biopsy Is Needed

Image-guided biopsy should be considered when:

• Imaging remains indeterminate despite MRI or CEUS 1
• The diagnosis would alter management significantly 1
• Patient has known malignancy and treatment decisions depend on confirmation 1

Critical Pitfalls to Avoid

Do not rely on single-phase or non-contrast CT alone—these have severely limited diagnostic accuracy (61-88% sensitivity for various metastases) compared to multiphase CT (85-91% detection rate) 1, 4.

Do not order CT with and without contrast—the unenhanced phase adds no diagnostic value for liver lesion characterization and doubles radiation exposure 4.

Do not assume all new liver lesions post-chemotherapy are metastases—focal nodular hyperplasia, regenerative nodules, and focal fatty infiltration are common benign findings after chemotherapy 1.

Radionuclide liver-spleen scan can resolve diagnostic confusion—a well-defined photon deficiency indicates neoplasm rather than focal fatty infiltration, which shows normal uptake 2, 6. However, this is now largely superseded by MRI and CEUS.

Special Consideration: Bevacizumab Effect

Be aware that liver metastases may undergo cystic change with antiangiogenic agents like bevacizumab, potentially mimicking benign hepatic cysts 1. This represents the opposite diagnostic dilemma where malignancy masquerades as benign disease.