In this study, we established three models to distinguish HCC from FNH in non-cirrhotic liver using four clinical factors and a Rad score, which was combined with eight radiomics features filtrated from arterial phase and portal venous phase on MRI. In comparison to the clinical model, the combined model showed overall superiority in the evaluation of accuracy, sensitivity, specificity, and AUC in both the training and validation sets (Table 2, Fig. 5). The addition of radiomics features improved the performance of the diagnostic model, but the radiomics model did not bring significant improvement compared to the clinical model.
Many previous studies have provided several ways to differentiate HCC from FNH. Li et al. [26] enrolled 38 patients with HCC and 65 with FNH to assess the diagnostic ability of contrast-enhanced US (ceUS) and microflow (MF) imaging and found that MF imaging had an excellent diagnostic performance in terms of differentiating between atypical HCC and FNH compared to routine ceUS. Yu et al. [27] included 42 HCCs and 16 FNHs and performed spectral CT during the arterial and portal venous phases, and found that CT spectral imaging increased the detectability and accuracy of differentiation between HCC and FNH. Nie et al. [28] developed and validated a CT-based radiomics nomogram for preoperative differentiation of FNH from HCC in livers without cirrhosis, achieving an AUC of 0.917 in the validation group. Several studies [29–31] have indicated that Gd-EOBDTPA-MRI is helpful for the diagnosis of FNH, as most FNHs show high- or iso- signal intensity (SI) compared to liver parenchyma in the hepatobiliary phase (HBP). However, Lee et al. [32] found that 85% of well-differentiated HCCs were hypointense on HBP, and about 15% of well-differentiated HCCs were iso- or hyperintense on HBP, illustrating that there is still some overlap between them, even in the HBP. In this study, we established a combined model for differential diagnosis of HCC from FNH in non-cirrhotic livers. Our model is non-invasive and easy to implement, and it achieved excellent performance with an AUC of 0.972 in the validation set.
In our study, the clinical model did not achieve the best AUC (0.937 and 0.903 in the training and validation sets, respectively), but it was still relatively high. Although we included as many of the radiological features that we could to help identify the two diseases as mentioned in the EASL Clinical Practice Guide for benign liver tumors, such as liver hemangioma, steatosis in lesions, and the liver, they turned out not to be strong predictors. Presence of a central scar is a typical feature of FNH, which is identified on MRI in approximately 30–50% of FNH cases [8]. On the other hand, about 50% of non-cirrhotic HCCs have a central scar that is detectable by MRI, especially in fibrolamellar carcinoma [33]. In our study, 32 % FNHs had the central scar, which was consistent with previous studies. Nevertheless, based on our results, we suggest that in the absence of available MRI, age, sex and HbsAg are the main reference indicators in making differential diagnosis between HCC and FNH in non-cirrhotic liver .
Our results were consistent with the study reported by Nie et al. [28] They also included only one radiological feature in their model, which was enhancement pattern, as we did. The epidemiological and clinical characteristics of these two diseases are also important references for differential diagnosis. FNH mainly occurs in females (up to 90% of cases), with an average age between 35 and 50 years. HCC mainly occurs in elderly males and is usually accompanied by hepatitis B virus infection. The three clinical factors (age, sex, and HbsAg) were consistent with the epidemiological differences between the two diseases, indicating the interpretability of our models.
Radiomics includes an enormous amount of data with high-dimensional characteristics, so it is important to know how to extract the key features from such a huge amount of data. In order to ensure the reproducibility of the selected features and avoid the interference by other subjective factors, we implemented rigorous feature selection in combination with machine learning. First, inter-observer and intra-observer agreements were evaluated, and features with an ICC > 0.8 were included. Second, two machine learning algorithms, mRMR and RF, were used for feature filtering. Third, a correlation analysis of the features screened by the two algorithms listed above was performed to exclude features of high correlation. Finally, LASSO regression, which is one of the most commonly used methods for dimensionality reduction in radiomics, was carried out to obtain the optimal radiomics signature.
Our study had several limitations. First, the number of samples was still limited compared to the large number of features. A large-scale clinical study enrolling more samples would help validate and improve the applicability of our model as an effective tool for differentiating between FNH and HCC. Second, external validation is needed to further verify the accuracy and clinical practicability of the model. Finally, sample selection bias was unavoidable in this retrospective study. Therefore, a prospective study should be conducted to further prove the practicability of the model.
In conclusion, our novel MR-based radiomics model demonstrated a powerful diagnostic capability because of its excellent performance, with a certain reference value for differentiating HCC from FNH in clinical studies.