Should fat in the radiofrequency ablation zone of hepatocellular adenomas raise suspicion for residual tumour?

To assess the significance of fat in the radiofrequency ablation (RFA) zone of hepatocellular adenomas (HCA), and its association with tumoral fat and hepatic steatosis. The radiological archive was searched for patients with ablated HCAs and follow-up magnetic resonance imaging between January 2008 and June 2014. Age, sex, risk factors and duration of clinical and imaging follow-up were recorded. Pre-RFA imaging was assessed for tumour size, intra-tumoral fat and steatosis. Post-RFA imaging was reviewed for size, enhancement and intra-ablational fat. Intra-ablational fat was classified as peripheral, central or mixed; the association of these distributions with steatosis and tumoral fat was assessed using Fisher's exact test. Sixteen patients with 26 ablated HCAs were included. Fat was present in 23/26 (88 %) ablation zones. Only 1/26 (4 %) showed serial enlargement and enhancement suggestive of residual disease; the enhancing area did not contain fat. All remaining ablations showed involution and/or diminishing fat content without suspicious enhancement (mean follow-up, 27 months; range, 2-84 months). The peripheral and mixed/central patterns of intra-ablational fat were associated with steatosis (P = 0.0005) and tumoral fat (P = 0.0003), respectively. Fat in the ablation zone of HCAs is a common finding which, in isolation, does not indicate residual tumour. Fat in the RFA zone of HCAs is a common finding on MRI. The distribution of fat is associated with hepatic steatosis and intra-tumoral fat. In isolation, intra-ablational fat of treated HCAs does not indicate residual tumour.