Nodular regenerative hyperplasia of the liver: coral atoll-like lesions on ultrasound are characteristic in predisposed patients.

Nodular regenerative hyperplasia (NRH) is an uncommon liver disease characterised histologically by numerous small hyperplastic nodules that are not separated by fibrotic tissue. It is thought to be the result of obliterative vasculopathy, and it has been associated with chronic use of medications, toxic substances and a wide variety of systemic diseases. Imaging diagnosis of early-stage NRH remains problematic. The nodules are rarely discerned and their appearance and behaviour before and after contrast medium administration are heterogeneous and not specific. A review of the literature shows that ultrasound has succeeded on occasion in revealing small focal liver lesions in patients with NRH. To our knowledge, there has been no published data on the performance in this setting of last-generation ultrasound scanners and techniques such as contrast-enhanced ultrasound (CEUS). The question is an important one because abdominal ultrasound is widely used as a first-line imaging technique for the evaluation of liver disease, and this makes it particularly suitable as a potential tool for the early diagnosis of NRH. Owing to the prolonged subclinical period and the limited help provided by imaging, the diagnosis in vivo of NRH is currently frequently missed, and it is still made exclusively on the basis of liver biopsy. In conclusion, this report describes 4 cases of biopsy-proven NRH that have been diagnosed over the past 2 years by our group. All were characterised by known comorbidities that confer a predisposition to NRH and by a peculiar parenchymal ultrasound pattern that we refer to as the "atoll sign".