Radiological Imaging Features of Fasciola hepatica Infection - A Pictorial Review

Abstract

Fascioliasis refers to a zoonosis caused by Fasciola hepatica, a trematode infecting herbivores, but also occurs in humans who ingest the metacercaria found in fresh water plants. Infection in humans is common in developing countries and is also not uncommon in Europe. Diagnosis of this infection is difficult, as the history and symptoms are nonspecific and stool analysis for eggs is negative until the disease is in an advanced state by when the parasite has reached the biliary system. The clinical course consists of two phases; first a hepatic parenchymal phase in which immature larvae invade the liver parenchyma, followed by a ductal phase characterized by the excretion of larvae into the bile ducts. Parenchymal Phase: Ultrasonography (US) findings are nonspecific in this early phase. Computerized tomography (CT) may demonstrate subcapsular low attenuation regions in the liver. Magnetic Resonance imaging (MRI) can also be utilized to establish liver parenchymal involvement, and is better than CT in characterizing hemorrhagic lesions, as well as identifying more lesions relative to CT. Ductal Phase: US examination is most useful at this stage, with its ability to demonstrate the live movement of the worms within the dilated ducts. A CT demonstrates dilated central biliary ducts with periportal tracking, whereas, mild ductal dilatation is poorly appreciated under MRI. Therefore, familiarity with the multimodality imaging features of fascioliasis, in combination with an available confirmatory enzyme-linked immunoassay, would be most helpful for early diagnosis.

Keywords: Fasciola hepatica; Fascioliasis; amoebic abscess; hydatid disease; pyogenic abscess; radiological imaging features.

Figure 1

Life cycle of F. hepatica.

Figure 2

A 38-year-old female with hepatic fascioliasis: Photomicrograph of a liver specimen shows parasitic granuloma with necrosis surrounded by heavy mononuclear and eosinophilic infiltration. Surrounding liver parenchyma shows fibrosis with inflammation (H and E, 40×).

Figure 3

High power (400×) view of an F. hepatica egg in a stool sample.

Figure 4

Parenchymal phase of fascioliasis. US shows a parenchymal focal lesion with a halo around it within the liver (arrow).

Figure 5

Periportal tracking. US shows linear hypoechogenicity (arrows) along the intrahepatic bile ducts.

Figure 6

F. hepatica worms. US demonstrates a linear echogenic material (arrow) within the dilated common hepatic duct representing a dead F. hepatica worm.

Figure 7

A contrast-enhanced CT scan demonstrates multiple, round, clustered, hypodense lesions, with peripheral contrast enhancement in the liver (arrow).

Figure 8

Infiltration of the liver in the early parenchymal phase. Contrastenhanced CT scan shows irregular low attenuation lesions (arrows) in the subcapsular portion of the (a) left and (b) right hepatic lobes (two different patients).

Figure 9

A contrast-enhanced CT scan shows low attenuation tracks (arrows) along the portal triads.

Figure 10

A CT scan shows (a, b) residual parenchymal calcification (arrow) after treatment, in a patient with F. hepatica.

Figure 11

(a) Axial and (b) coronal T2W MR images show more prominent serpigineous hyperintense lesions in the liver (arrows in a) and a hyperintense glisson capsule (arrows in b).

Figure 12

A contrast-enhanced T1W MR image shows multiple, round, clustered hypodense lesions with peripheral contrast enhancement (arrow) in the liver (same patient in Figure 7)

Figure 13

A T2W axial MR image shows hyperintense tracks (arrows) along the portal veins.

Figure 14

F. hepatica worms. T2W coronal MR image shows mild dilatation of the common bile duct, and a filling defect (arrow).

Figure 15

Complicated parenchymal lesions: Abscess formation, (a) US demonstrates an irregular-shaped lesion containing heterogeneous anechoic areas (arrows). (b) A contrast-enhanced CT scan shows (same patient) an irregular heterogeneous lesion with irregular peripheral enhancement (arrows).

Figure 16

Complicated parenchymal lesions: Hemorrhagic infarction: (a) T1W in-phase MR image shows rim-shaped hyperintense lesion (arrow). (b) T1W out-of-phase MR image shows rim-shaped hyperintensity without signal loss (arrow).

Figure 17

Amebic liver abscess.(a) Non-contrast and (b) Contrast-enhanced CT scan demonstrates a large, lobulated, well-defined cystic mass in the right hepatic lobe, with enhanced thick wall (arrow), and a satellite cystic mass associated with the same imaging features.

Figure 18

A contrast-enhanced CT scan demonstrates a large, multilocular hydatid cyst in the right hepatic lobe, with multiple daughter cysts (arrow). Note a subtotally calcified lesion in the seventh segment of the liver (arrow head).

Figure 19

Pyogenic multiple liver abscesses.(a) Contrast-enhanced CT scan shows multiple hypoattenuating lesions representing pyogenic abscesses scattered throughout the liver. These lesions demonstrate peripheral enhancement and surrounding edema. (b) Coronal MR T2W HASTE images and (c) contrast-enhanced MR images show multiple small hyperintense nodules representing pyogenic microabscesses disseminated in the liver, with peripheral contrast enhancement.