To evaluate the diagnostic value of contrast-enhanced ultrasound (CEUS) for rare focal liver diseases (FLLs), and to explore the diagnostic value of the "fast-forward and fast-out" pattern on CEUS in rare FLLs.

A retrospective analysis was performed on the contrast-enhanced ultrasound data of FLL patients at Tongji Hospital Affiliated to Tongji Medical College, Huazhong University of Science and Technology from January 2012 to August 2019 to identify lesions with a population incidence rate of＜0.05%. A total of 66 such rare lesions were identified, 33 of which were examined by MRI/CT. Using the pathological results as the gold standard, a four-fold table was used to evaluate the diagnostic performance of ultrasound angiography, MRI/CT examination, and their combination for rare benign and malignant FLLs, and χ² test was used to compare the difference in diagnostic accuracy between different examination methods.

Among the 61 rare FLLs, the sensitivity, specificity, positive predictive value, negative prediction value, and accuracy of CEUS for the diagnosis of benign and malignant lesions were 51.9% (28/54), 85.7% (6/7), 96.6% (28/29), 18.8% (6/32), and 55.7% (34/61), respectively. Among the 33 rare FLLs, the diagnostic accuracy of CEUS was slightly higher than that of MRI/CT, but the difference was not statistically significant (48.5% vs 39.4%, P＞0.05). The diagnostic accuracy of CEUS + MRI/CT for rare benign and malignant FLL (69.7%) was significantly higher than that of MRI/CT or CEUS alone (χ²=6.111, P=0.013; χ²=3.070, P=0.046). For the rare FLLs presenting with the "fast forward and fast out" pattern on CEUS, the diagnostic accuracy of CEUS was 18.8% (6/32). In the actual work, after the combination of clinical manifestations and laboratory tests, the diagnostic accuracy was 56.3% (18/32), which was higher than that of CEUS alone (χ²=9.600, P=0.002).

CEUS has appreciated diagnostic value for rare FLLs, which is comparable to that of MRI/CT. For the diagnosis of rare FLLs that exhibit the "fast-forward and fast-out" pattern on CEUS, it is helpful to improve the diagnostic accuracy by combining with clinical manifestations.