What type of computed tomography (CT) scan is recommended for a patient with transaminitis and fatty liver disease to further characterize the liver?

CT Imaging for Transaminitis and Fatty Liver

For a patient with transaminitis and fatty liver disease, you should NOT routinely order CT imaging for further liver characterization, as CT has limited diagnostic value in this clinical context. 1, 2

Why CT is Not the Optimal Choice

The American College of Radiology guidelines specifically address chronic liver disease and fatty liver evaluation, and CT imaging receives relatively low appropriateness ratings in this scenario 1:

• CT abdomen with IV contrast receives a rating of only 5 out of 9 (may be appropriate) for chronic liver disease assessment 1
• CT abdomen without IV contrast receives a rating of 4 out of 9 (may be appropriate) 1
• CT abdomen without and with IV contrast receives a rating of 4 out of 9 (may be appropriate) and delivers higher radiation exposure 1

The American College of Radiology explicitly states that CT with and without IV contrast is not recommended because unenhanced images add no diagnostic value for liver characterization. 1, 3

Superior Alternative Imaging Modalities

First-Line Recommendation: MRI

MRI abdomen without and with IV contrast is the preferred imaging modality, receiving a rating of 6 out of 9 from the American College of Radiology for chronic liver disease assessment. 1

Key advantages of MRI include:

• Chemical shift-encoded MRI is the most accurate and precise method for liver fat quantification 4
• MRI with gadolinium differentiates between common benign lesions in 70% of cases 2
• MRI establishes a definitive diagnosis in 95% of liver lesions, significantly higher than CT 5
• MRI with hepatobiliary contrast also receives a rating of 6 out of 9 and can be performed with MR elastography to simultaneously assess fibrosis 1

Second-Line Option: Ultrasound

Ultrasound abdomen receives a rating of 6 out of 9 from the American College of Radiology for chronic liver disease assessment. 1

Important caveats about ultrasound:

• Sonographic appearance of hepatic steatosis and cirrhosis often overlap, with significant interobserver variability 1
• Ultrasound can be performed with acoustic radiation force impulse (ARFI) elastography to assess fibrosis 1
• Sensitivity is limited in patients with obesity or nodular cirrhotic livers 1

When CT Might Be Considered

Specific Clinical Scenarios

If you must use CT imaging (e.g., MRI contraindicated, urgent assessment needed), order multiphase contrast-enhanced CT (triphasic CT) with arterial and portal venous phases, NOT single-phase or unenhanced CT. 2, 3

Triphasic CT provides superior diagnostic accuracy of 95.5% compared to standard single-phase IV contrast CT, which has accuracy of only 74-95%. 3

The three phases should include:

• Arterial phase
• Portal venous phase
• Delayed phase 1, 2

Technical Requirements

• Slice thickness of 2.5-5 mm for adequate lesion detection 2, 3
• Proper contrast bolus timing is critical 3

Important Diagnostic Limitations of CT

CT has significant limitations for fatty liver assessment on contrast-enhanced studies:

• Comparing hepatic and splenic attenuation on postcontrast CT results in only 30% specificity and 20% positive predictive value for fatty liver 6
• Fatty liver can only be reliably diagnosed on contrast-enhanced CT if liver appears less attenuating than muscle, which occurs only with pronounced fatty infiltration 6
• Limited unenhanced hepatic CT remains the optimal CT technique for detection of fatty infiltration, but this is still inferior to MRI 7
• Differential liver-spleen attenuation criteria are protocol-specific and time-dependent, with overlap between healthy subjects and patients with fatty liver 7

Clinical Context Matters

The appropriateness of imaging depends on your specific clinical concern:

If Screening for Hepatocellular Carcinoma (HCC)

• MRI abdomen without and with IV contrast receives a rating of 8 out of 9 1
• CT abdomen with IV contrast receives a rating of 7 out of 9 1
• Consider surveillance by CT or MRI when ultrasound is limited by obesity, NAFLD, or nodular cirrhotic liver 1

If Evaluating for Cirrhosis

• MRI with MR elastography is superior to CT 1
• MRI can assess for cirrhosis and perform elastography simultaneously 1

Common Pitfalls to Avoid

• Do not order CT without contrast alone - it has minimal diagnostic value for liver lesion characterization 1, 2
• Do not order CT with and without contrast - the unenhanced phase adds no value and doubles radiation exposure 1, 3
• Do not rely on visual assessment of liver attenuation relative to spleen on contrast-enhanced CT - this has poor specificity for fatty liver 6
• Avoid single-phase contrast CT - if using CT, always obtain multiphase imaging 3