[Alveolar echinococcosis: how to confirm the diagnosis?]

Ultrasonography is the first-step exam for the diagnosis of alveolar echinococcosis. Liver involvement commonly appears as an ill-defined infiltration of the liver parenchyma. Lesions are heterogeneous and in most cases hyperechoic, related to fibro-parasitic tissue associated to scattered calcifications. Hypoechoic foci can also be observed, related to necrosis. In 25 % of the cases, ultrasonography discovers atypical aspects that must be known by radiologists working in endemic region for alveolar echinococcosis. Specific serological tests, particularly ELISA and western blot, usually confirm the diagnosis. Therefore, per-cutaneous punction is exceptionally needed to assess the diagnosis. Other imaging techniques are very useful to complete the diagnosis step and to specify vascular and biliary extension, a crucial information for the therapeutic choice. Computed tomography may show small additional parasitic foci, non visualized by ultrasonography. It allows an accurate examination of the lesions particularly in case of very calcified images that could have made ultrasonographic analysis more difficult. Magnetic resonance imaging may be useful for diagnosis showing on T2 weighted images, in cases of fertile lesions, numerous clustered small cysts. Moreover, it is an excellent technique to analyse vascular involvement, particularly for vena cava and hepatic veins, and to diagnose involvement of adjacent organs. Coupled to cholangio-MR, it allows a precise examination of the biliary tree invasion, particularly in the hilum area.