Small (< or = 2 cm) atypical hepatic haemangiomas in the non-cirrhotic patient: pattern-based classification scheme for enhancement at triple-phase helical CT [Emangiomi epatici atipici di piccole dimensioni (≤2 cm) nel paziente non-cirrotico: classificazione in base al pattern di enhancement in TC spirale trifasica]

Abstract PURPOSE: The aim of this study was to determine by triplephase helical computed tomography (CT) the appearance of atypical small (< or = 2 cm) hepatic haemangiomas (HHs) in the non-cirrhotic patient. MATERIALS AND METHODS: We retrospectively reviewed the hepatic arterial-dominant phase (HAP), portal venous phase (PVP) and delayed-phase (DP) helical CT images of 47 patients with 52 atypical small (< or = 2 cm) HHs associated with 34 typical small HHs. Images were assessed to identify the patterns of enhancement of atypical HHs and correlate their appearance with that of typical small HHs in the delayed phase. Interobserver variability and kappa value were calculated. Statistical significance was calculated by the Fisher exact test. RESULTS: The 52 atypical small HHs were categorised as follows: type 1a (hyperattenuating in the HAP, n=17), type 1b [hyperattenuating with transient hepatic attenuation difference (THAD) around the lesion in the HAP, n=12], type 2a (homogeneously hypoattenuating in the HAP or PVP, n=9), type 2b (hypoattenuating with "bright-dot" sign in the HAP or PVP, n=13) and type 3 (hypoattenuating with central enhancing area, n=1). Interobserver agreement was perfect for HHs of types 1a, 1b, 2a and 3. On DP images, the appearance of atypical small HHs was identical to that of typical small HHs in all cases (p<0.0001), with lesions showing homogeneous isoattenuation to the aorta or liver parenchyma without peripheral capsule. CONCLUSIONS: Triple-phase helical CT scans can distinguish several types of atypical small HHs. The demonstration of patterns similar to those of typical forms on DP CT is fundamental for the diagnosis.