Hepatic Echinococcal Cysts: A Review

Abstract

Cystic echinococcosis (CE) is a widely endemic helminthic disease caused by infection with metacestodes (larval stage) of the Echinococcus granulosus tapeworm. E. granulosus are common parasites in certain parts of the world, and are present on every continent with the exception of Antarctica. As a result, a large number of people are affected by CE. The increased emigration of populations from endemic areas where prevalence rates are as high as 5-10% and the relatively quiescent clinical course of CE pose challenges for accurate and timely diagnoses. Upon infection with CE, cyst formation mainly occurs in the liver (70%). Diagnosis involves serum serologic testing for antibodies against hydatid antigens, but preferably with imaging by ultrasound or CT/MRI. Treatment methods include chemotherapy with benzimidazole carbamates and/or surgical approaches, including percutaneous aspiration injection and reaspiration. The success of these methods is influenced by the stage and location of hepatic cysts. However, CE can be clinically silent, and has a high risk for recurrence. It is important to consider the echinococcal parasite in the differential diagnosis of liver cystic lesions, especially in patients of foreign origin, and to perform appropriate long-term follow-ups. The aim of this review is to highlight the epidemiology, natural history, diagnostic methods, and treatment of liver disease caused by E. granulosus.

Keywords: Anaphylaxis; Echinococcus; Hydatid cyst; Tapeworm.

Fig. 1.. Unilocular hepatic hydatid cyst (blue arrow) on CT and MRI.

A: Contrast-enhanced CT: cystic lesion is hypodense with a thickened, enhancing rim; B: T2-weighted MRI: cystic mass is hyperintense with characteristic low-signal intensity rim, probably representing the collagen-rich, outer layer (pericyst) of the hydatid cyst; C. Noncontrast T1-weighted MRI with fat saturation: cystic lesion is hypointense; D: Postcontrast T1-weighted MRI with fat saturation: cystic lesion demonstrates an enhancing rim similar to CT (in panel A), and is without distinct enhancing internal components.

Fig. 2.. Superior view of partially calcified hepatic hydatid cyst on CT and MRI (same patient as in Fig. 1).

A: Contrast-enhanced CT: hypodense cystic lesion with partially calcified rim and internal components; B: T2-weighted MRI: cystic lesion is mildly hyperintense with low-signal intensity rim and internal components; low-signal intensity is likely due to a combination of calcification and the collagen-rich pericyst; C: Noncontrast T1-weighted MRI with fat saturation: cystic lesion is hypointense; D: Postcontrast T1-weighted MRI with fat saturation: cystic lesion demonstrates an enhancing rim without distinct enhancing internal components. Note: calcification is often inconspicuous on MRI.

Fig. 3.. Contrast-enhanced CT.

Complex fluid collection with curvilinear densities (blue arrow), consistent with detachment of the laminated membranes of the endocyst from the pericyst of a hepatic hydatid cyst.

Fig. 4.. Management algorithms for cystic echinococcosis.,,,,

A: Diagnostic approaches; B: Therapeutic approaches. IB, Immunoblot; IEP, Immunoelectrophoresis.