Background: Hepatocellular carcinoma (HCC) is the most common primary liver malignancy. Magnetic resonance imaging has been widely used for detection and characterization of HCC. Objective: Describe MRI findings of HCC and to define the typical and atypical appearances of HCC on magnetic resonance images. Methods: We retrospectively reviewed MRI findings of 100 HCC in 78 patients. Diagnosis was confirmed by angiography, pathology or follow up imaging. The signal intensity, size, margins, enhancement pattern, and other features were evaluated. Imaging findings between small HCC (< 2 cm) and large HCC (>2 cm) were compared. Results: The most common signal intensity of HCC on unenhanced T1- and T2-weighted images was hypointense on T1-weighted images and hyperintense on T2-weighted images (65%). Most HCC (91%) were hyperintense on T2-weighted images. Isointensity on T2-weighted images were found in 9% of HCC. The typical enhancement pattern of HCC was enhancement on the arterial phase and washout on the portovenous phase (84%). Atypical enhancement pattern of HCC were enhancement on the portovenous phase in 5%, rim enhancement on the arterial phase or portovenous phase were demonstrated in 2%. Hyperintensity of the tumor on delayed phase was found in 19%. There was no statistically significant difference in signal intensity, enhancement, and washout pattern between small and large HCC. Fatty metamorphosis, mosaic pattern, necrosis, capsule and vascular involvement were found in 18%, 42%, 5%, 62%, and 6%, respectively. Mosaic pattern, necrosis, capsule, and vascular involvement were observed more frequently in large HCC. Conclusion: The typical appearance of HCC was hypointense on T1-weighted, hyperintense on T2-weighted images, arterial enhancement and portovenous washout. Atypical appearances of HCC were rim enhancement on the arterial phase or portovenous phase and persistent enhancement on the delayed phase
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