MR Elastography for Suspected Early Cirrhosis After Normal CT
In a stroke patient with normal CT but suspected early cirrhosis, proceed directly to MR elastography, which is the single most accurate imaging modality for detecting and staging hepatic fibrosis before structural changes become visible on conventional imaging. 1, 2
Why CT Cannot Exclude Early Cirrhosis
CT has intrinsically low sensitivity for detecting both cirrhosis and non-cirrhotic fibrosis, even when evaluating multiple morphologic features together (surface nodularity, caudate hypertrophy, right-lobe atrophy), because these structural alterations do not manifest until fibrosis has progressed to an advanced stage. 2
Non-contrast CT only demonstrates gross structural changes in very advanced disease, making it ineffective for early diagnosis. 2
Contrast-enhanced CT can show parenchymal heterogeneity and lattice-like fibrosis bands but still fails to identify earlier stages of cirrhosis. 2
A normal CT should never be used to exclude early cirrhosis when clinical suspicion is high based on risk factors, laboratory findings, or symptoms. 2
MR Elastography as the Definitive Next Step
MR elastography directly measures liver stiffness, allowing detection of fibrosis before morphologic changes become visible on conventional imaging, making it superior to all other modalities when CT appears normal but clinical suspicion remains. 1, 2
MR elastography achieves 73-91% sensitivity and 79-85% specificity across all stages of fibrosis, with the unique ability to distinguish intermediate stages (F2-F3) that other modalities miss. 3
MR elastography evaluates almost the entire liver volume and maintains excellent accuracy in obese patients and those with ascites, where ultrasound-based methods frequently fail. 3
MR elastography can simultaneously screen for hepatocellular carcinoma during the same examination, providing additional diagnostic value. 3
Important Limitations and Confounders
Hepatic iron deposition reduces MR elastography accuracy due to susceptibility artifacts and can result in undersampling or nondiagnostic evaluations. 1, 2
Performance may be compromised at 3-Tesla field strength. 1, 2
Liver stiffness measurements can be confounded by parenchymal edema, inflammation, cholestasis, cardiogenic hepatic congestion, and recent food intake—ensure patients are fasting and consider these factors when interpreting results. 1, 2
Alternative if MR Elastography is Unavailable
If MRI is contraindicated or unavailable, ARFI ultrasound elastography is the preferred alternative, with significantly lower failure rates (2.1%) compared to transient elastography (6.6%, P < 0.001). 3
ARFI functions effectively in obese patients, those with ascites, and NAFLD patients where transient elastography frequently fails. 3
Stiffness measurement thresholds for ultrasound elastography: <8.0 kPa rules out advanced fibrosis; 8-12 kPa suggests advanced fibrosis requiring hepatology evaluation; >12.5 kPa indicates cirrhosis requiring urgent hepatology referral and HCC screening. 3
Combining Methods for Indeterminate Results
When elastography results are indeterminate (8-12 kPa on ultrasound), combine with serum biomarkers (FIB-4 or NAFLD Fibrosis Score) to improve diagnostic accuracy and potentially avoid liver biopsy. 3
In this stroke patient with NVAF, note that FIB-4 >3.25 is associated with severe stroke, major disability, and all-cause mortality, making early fibrosis detection particularly important for prognostication. 4
What NOT to Do
Do not repeat CT imaging (with or without contrast) as it does not improve diagnostic accuracy for early fibrosis. 2
Do not rely solely on serum fibrosis markers (AST/platelet ratio, FIB-4) as definitive tests, given their inaccuracy for intermediate fibrosis stages. 2
Do not proceed directly to liver biopsy without first attempting non-invasive elastography, due to biopsy cost, sampling error, morbidity risk (including bleeding risk in stroke patients on anticoagulation), and limited suitability for longitudinal monitoring. 1, 2