Abstract: Objective The aim of this study was to explore imaging feature of atypical hepatic abscess (AHA) for early diagnosis. Methods 42 patients with AHA and 42 patients with intrahepatic metastatic tumor (IMT) were encountered in our hospital between January 2019 and January 2024, and all underwent MRI and diffusion-weighted imaging (DWI) scan. Plain and enhanced scan signals, DWI signals, enhancement features at arterial phase, apparent diffusion coefficient (ADC) and relative ADC (rADC) of solid part in lesion margin were compared between the two groups. Results Proportion of target-like high signals by DWI in AHA lesions was significantly lower than that in IMT lesions (64.3% vs. 90.5%(P＜0.05); proportions of margin enhancement at arterial phase and uneven enhancement at portal vein phase and at equilibrium phase in AHA lesions were 45.2%, 71.4% and 23.8%, significantly lower than 76.2%, 100.0% and 88.1% (P<0.05) in the IMT lesions; proportions of significant enhancement and continuity interruption at arterial phase were 9.5% and 0.0%, significantly lower than 88.1% and 73.8% (P<0.05) in IMT lesions; ADC and rADC of solid parts at AHA lesion margin were (1.8±0.4) ×10^-3mm²/s and (0.7±0.2) ×10^-3mm²/s, both significantly higher than [(1.0±0.2) ×10^-3mm²/s and (0.4±0.1) ×10^-3mm²/s, P<0.05] at IMT lesions. Conclusion AHA lesions at routine MRI and DWI scan has a unique feature, by which clinicians might differentiate it from IMT lesions.

Key words: Atypical hepatic abscess, Hepatic metastasis, Routine MRI, Diffusion-weighted imaging, Apparent diffusion coefficient, Diagnosis