Alveolar echinococcosis: correlation between hepatic MRI findings and FDG-PET/CT metabolic activity

To correlate the appearance of alveolar echinococcosis (AE) hepatic lesions in magnetic resonance imaging (MRI) as defined by Kodama, to the metabolic activity visualized in 18-fluoro-deoxyglucose positron emission tomography combined with computed tomography (PET/CT). Forty-two patients diagnosed with AE and who underwent both MRI and PET/CT were included. The forty-two hepatic lesions were divided into five types according to Kodama's classification by three independent readers blinded with regard to the PET/CT information. Concerning PET/CT, two independent readers, unaware of the MRI information, considered the results as positive when an increased FDG-uptake was observed at 1 or 3 h after FDG-injection, and as negative when no increased uptake was noted. Inter-observer agreement was assessed by using kappa statistics. Forty-two lesions were counted and the mean diameter of overall evaluated lesions was 6.3 cm. One lesion (2.4%) was categorized as type 1, 11 (26.2%) as type 2, 24 (57.1%) as type 3, 3 (7.1%) as type 4, and 3 (7.1%) as type 5. The inter-observer analysis found a kappa coefficient of 0.96. All type-1, 90.9% of type-2 and 87.5% of type-3 lesions showed an increased FDG-uptake on PET/CT images. All non-microcystic AE liver lesions (types 4 and 5) showed no abnormal increased FDG-uptake on PET/CT images. The inter-observer analysis at 1 and 3 h found a kappa coefficient of 0.95 and 0.92, respectively. In patients with AE liver lesions, the absence of microcysts on MRI is strongly correlated to a metabolically inactive disease.