Multimodality imaging in diagnosis and management of alveolar echinococcosis: an update

Abstract

Alveolar echinococcosis is a parasitic disease limited to the northern hemisphere. The disease occurs primarily in the liver and shows a profile mimicking slow-growing malignant tumors. Echinococcus multilocularis infection is fatal if left untreated. It can cause several complications by infiltrating the vascular structures, biliary tracts, and the hilum of the liver. As it can invade the adjacent organs or can spread to distant organs, alveolar echinococcosis can easily be confused with malignancies. We provide a brief review of epidemiologic and pathophysiologic profile of alveolar echinococcosis and clinical features of the disease. This article focuses primarily on the imaging features of alveolar echinococcosis on ultrasonogra-phy, computed tomography, magnetic resonance imaging, diffusion-weighted imaging and positron emission tomography-computed tomography. We also reviewed the role of radiology in diagnosis, management, and follow-up of the disease.

Figure 1

A 40-year-old man with hepatic alveolar echinococcosis. An oblique sonogram obtained through the right liver lobe shows a heterogeneous mass lesion with indistinct borders. The mass contains hyperechoic foci of calcification with posterior acoustic shadowing (arrowheads).

Figure 2. a, b

A 66-year-old male with E. multilocularis infection of the right and the left liver lobes. Gray-scale US image (a) from the left lobe of the liver shows a highly calcified heterogeneous lesion (arrowheads). Note that the posterior border of the parasitic mass is obscured due to strong posterior acoustic shadowing. Abdominal CT image (b) obtained after the administration of intravenous contrast depicts two hepatic masses with indistinct margins including diffuse hyperdense foci of coarse calcification.

Figure 3. a, b

A 39-year-old man with complicated E. multilocularis infection of the liver. Contrast-enhanced axial CT image (a) shows a huge mass with a central fluid filled area. Right portal vein and right and middle hepatic veins are invaded by the parasitic mass (not shown). The lesion also compresses the left portal vein branch (not shown). Axial maximum intensity projection (MIP) CT image (b) demonstrates a collapsed cavity in the right hepatic lobe with a pigtail drain inserted. This 10F percutaneous drainage catheter was easily placed into the cavity under sonographic guidance. After placement of the catheter, 3000 mL of infected fluid was drained.

Figure 4. a, b

A 29-year-old man with alveolar echinococcosis involvement of the liver and the right adrenal gland. Axial contrast-enhanced CT image (a) demonstrates an infiltrating tumor-like hepatic mass including a few scattered hyperattenuating foci of calcification and large areas of hypoattenuation corresponding to necrosis. Diffuse enlargement of the right adrenal gland containing numerous cysts with thin walls is present on this CT image (arrowheads). Note that the walls of cysts within the gland show mild enhancement. The left adrenal gland is normal. A coronal contrast-enhanced MIP image (b) reveals severe narrowing of the intrahepatic inferior vena cava (arrow).

Figure 5. a, b

A 47-year-old man with recurrent hepatic alveolar echinococcosis disseminated in the scapula, humeral head, and soft tissues. Axial unenhanced follow-up CT image demonstrated a cystic mass with thick walls adjacent to the area of surgery compatible with disease recurrence (not shown). An axial image with bone window from unenhanced chest CT (a) shows diffuse expansile lytic lesions of the scapula and the head of the humerus. Unenhanced sagittal multiplanar reformatted (MPR) CT image (b) shows multiple large well-marginated cystic parasitic lesions (arrowheads) within subcutaneous tissue and muscle planes of the right shoulder.

Figure 6

Illustrative scheme of Kodama’s MRI classification system for hepatic alveolar echinococcosis lesions. Adapted from Kodama et al. (30).

Figure 7. a, b

A 53-year-old woman with alveolar echinococcosis of the liver involving the biliary tree. Axial T2-weighted image (a) reveals a big homogeneously hypointense mass and marked dilatation of biliary ducts. A coronal thin-section image from magnetic resonance cholangiopancreatography (b) shows the hepatic mass compressing the hilar biliary ducts. Note the apparent intrahepatic biliary dilatation.

Figure 8. a, b

A 21-year-old female with disseminated E. multilocularis infection. Axial MRI scans show a tumor-like mass with irregular margin in the left cerebellar hemisphere. The lesion is seen inhomogeneously hypointense on T2-weighted image (a). An area of edema surrounding the parasitic lesion is seen. Note multiple tiny cysts in the lesion (arrowheads). Axial T1-weighted postcontrast image (b) demonstrates irregular rim-like peripheral enhancement on the border of the mass.

Figure 9. a–e

A 55-year-old woman with metastatic E. multilocularis infection. Chest CT showed large pulmonary nodules. One of these nodules located medially showed cavitation and the other lesion contained a small focus of calcification (not shown).The evaluation of pulmonary nodules in whole-body 18F-FDG PET-CT scan (a) demonstrates apparent increased metabolic activity in the paramediastinal cavitary nodule (arrow). PET-CT examination of the chest (b) also shows increased FDG uptake in a small area of the third rib (arrow). A fused PET-CT image (c) obtained from upper abdomen shows multiple metabolically active hepatic foci (arrowheads). These PET-CT (+) areas correspond to periparasitic granuloma around metacestodal cysts (arrowheads) that are best seen on an axial T2-weighted image (d). Note the multifocally increased FDG uptake in the periphery of the lesion, while its center does not take up FDG in PET-CT imaging (e), compatible with extensive necrosis.

Figure 10. a, b

A 34-year-old man with recurrent disseminated E. multilocularis infection after right hepatectomy. An axial contrast-enhanced follow-up abdominal CT (a) reveals masses that emerged close to the operation site (asterisk) and the right adrenal gland (arrowheads). Note that the adrenal mass contains two small foci of calcification. Sagittal MPR CT image (b) demonstrates multiple pulmonary lesions that developed due to spread of the parasitic mass via the transdiaphragmatic pathway (arrow).