CT-derived extracellular volume (ECV) fraction for hepatocellular adenoma and FNH

Hepatocellular adenoma (HCA) and focal nodular hyperplasia (FNH) are two types of benign liver lesions that can sometimes be difficult to differentiate based on imaging studies due to overlapping features. CT-derived extracellular volume (ECV) fraction has emerged as a valuable quantitative imaging biomarker to distinguish between these two entities more accurately and noninvasively.

### **What is Hepatocellular Adenoma (HCA)?**

Hepatocellular adenoma is a rare benign liver tumor that predominantly occurs in women, often associated with hormonal factors such as oral contraceptive use or anabolic steroid use. HCA carries a risk of complications, including hemorrhage and malignant transformation, making accurate diagnosis critical for appropriate management.

### **What is Focal Nodular Hyperplasia (FNH)?**

Focal nodular hyperplasia is another benign liver lesion that is more common than HCA and typically occurs in women of reproductive age. It is considered a hyperplastic response to abnormal vascular flow rather than a true neoplasm. FNH is generally asymptomatic and has no risk of malignant transformation, making it less concerning from a clinical perspective compared to HCA.

### **Differentiating Features of HCA and FNH**

Differentiating HCA from FNH can be challenging due to overlapping imaging characteristics on conventional modalities such as ultrasound, CT, or MRI. However, there are some distinguishing features:

• **HCA**: Typically appears as a well-circumscribed, homogenous lesion on imaging. It lacks a central scar and may show hemorrhage or fat deposition.
• **FNH**: Often presents with a central stellate scar and radiating fibrous septa. It may display a "spoke-wheel" pattern of enhancement due to its vascular nature.

### **Role of CT-Derived Extracellular Volume (ECV) Fraction**

The extracellular volume fraction is a quantitative imaging parameter derived from unenhanced and equilibrium phase CT images. It reflects the proportion of extracellular space within a tissue and has shown promise in distinguishing between HCA and FNH.

#### **Study Findings on ECV Fraction**

1. **ECV Fraction in FNH vs. HCA**:

• The mean ECV fraction was significantly higher in FNH (37.7% ± 8.8%) compared to HCA (26.7%, interquartile range 22.5%–31%).
• This difference was statistically significant (P = .001).

2. **Optimal Cutoff Value**:

• A cutoff value of 32.25% was determined to differentiate FNH from HCA.
• Sensitivity: 76.5%
• Specificity: 78.9%
• Area under the ROC curve (AUC): 0.824 (95% CI: 0.675–0.972, P = .001), indicating strong diagnostic accuracy.

3. **Reproducibility**:

• The interobserver agreement for ECV fraction measurements was excellent, with intraclass correlation coefficients of 0.884 for HCA and 0.915 for FNH.

#### **Clinical Implications**

• **High Diagnostic Accuracy**: The ECV fraction provides strong performance metrics for distinguishing between HCA and FNH, reducing diagnostic uncertainty.
• **Noninvasive Biomarker**: The technique is noninvasive, which can minimize the need for liver biopsies and invasive procedures.
• **Improved Diagnostic Confidence**: ECV fraction analysis can improve diagnostic confidence for radiologists and clinicians, aiding in appropriate patient management.

### **Conclusion**

CT-derived ECV fraction is a promising imaging biomarker for differentiating hepatocellular adenoma (HCA) from focal nodular hyperplasia (FNH). With high accuracy, reproducibility, and diagnostic reliability, it offers a noninvasive alternative to invasive procedures like biopsies. The quantitative approach of ECV fraction measurement enhances the ability to make precise diagnoses, ultimately improving patient care and reducing unnecessary interventions.