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

OBJECTIVES: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSION: Fat in the ablation zone of HCAs is a common finding which, in isolation, does not indicate residual tumour.

KEY POINTS: • 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.