Abstract
Hepatic Alveolar Echinococcosis (HAE), caused by larvae of Echinococcus multilocularis, is a rare but potentially lethal parasitic disease. The first diagnostic suspicion is usually based on hepatic ultrasound exam performed because of abdominal symptoms or in the context of a general checkup; HAE diagnosis may thus also be an incidental finding on imaging. The next step should be Computed Tomography (CT) or Magnetic Resonance Imaging (MRI). They play an important role in the initial assessment of the disease; with chest and brain imaging, they are necessary to assess the PNM stage (parasite lesion, neighboring organ invasion, metastases) of a patient with AE. Performed at least yearly, they also represent key exams for long-term follow-up after therapeutic interventions. Familiarity of radiologists with HAE imaging findings, especially in the endemic regions, will enable earlier diagnosis and more effective treatment. Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) is currently considered to be the only noninvasive, albeit indirect, tool for the detection of metabolic activity in AE. Delayed acquisition of images (3 hrs after FDG injection) enhances its sensitivity for the assessment of lesion metabolism and its reliability for the continuation/withdrawal of anti-parasite treatment. However, sophisticated equipment and high cost widely limit PET/CT use for routine evaluation. Preliminary studies show that new techniques, such as contrast-enhanced ultrasound (US), Dual Energy CT or Spectral CT, and Diffusion-Weighted MRI, might also be useful in detecting the blood supply and metabolism of lesions. However, they cannot be recommended before further evaluation of their reliability in a larger number of patients with a variety of locations and stages of AE lesions.
Highlights
Hepatic Alveolar Echinococcosis (HAE) caused by the larvae of Echinococcus multilocularis is a rare disease only present in the northern hemisphere, compared with Cystic Echinococcosis (CE) caused by Echinococcus granulosus, which is present worldwide
Because HAE is a tumor-like and chronic disease, with a latent stage that may last for years before signs and symptoms develop, the diagnosis primarily depends on imaging techniques including ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) [4, 32]
More sophisticated imaging techniques, such as Contrast-Enhanced Ultrasound (CEUS), dual energy Computed Tomography (CT) and spectral CT, or MR-Diffusion-Weighted Imaging (DWI), have become available; some of them could be promising in their applications to HAE
Summary
Hepatic Alveolar Echinococcosis (HAE) caused by the larvae (metacestode) of Echinococcus multilocularis is a rare disease only present in the northern hemisphere, compared with Cystic Echinococcosis (CE) caused by Echinococcus granulosus, which is present worldwide. Because HAE is a tumor-like and chronic disease, with a latent stage that may last for years before signs and symptoms develop, the diagnosis primarily depends on imaging techniques including ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) [4, 32]. This review will focus on the images obtained from well-validated imaging techniques in HAE and when each technique should be used for diagnosis and follow-up It will describe the images obtained with newer imaging procedures recently introduced and try to delineate their pathological counterpart. Whenever possible, it will tentatively establish their additional value, if any, for diagnosis and follow-up
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