LAUSR

Van Aalten et al. first described the atoll sign in 2011. They found this was present in 43% of the inflammatory subtype of hepatocellular adenomas (HCA), but not in any of the other subtypes. They described the atoll sign on T2weighted MR images, as being characterized by a hyperintense signal band in the periphery of the lesion and isointensity of the center of the lesion with respect of the surrounding liver. They postulated that the atoll sign may be due to sinusoidal dilatation within inflammatory HCA. The new classification of hepatocellular adenomas, published in 2007, identifies 4 subtypes. HNF1A-mutated HCA represents 30–40% of HCAs; b-cateninmutated HCA represents 10–15%; inflammatory HCA represents 40–50%; and unclassified HCA represents 10–25%. In a review of hepatocellular adenomas, Thomeer et al. reported that HCAs have a rupture rate of 16% (usually in lesions over 5cm in size) and a malignant conversion rate of 4.2%(although they report that this is likely an overestimate).