Imaging Diagnosis

Considering the size of the adult F. hepatica flukes and their presence in the bile ducts of millions of people in scattered endemic foci throughout the world, it is surprising that they are identified radiologically only occasionally, and only in recent years when ultrasound and CT scanning have become more widely available and more utilized in diseases of the hepatobiliary system. As already noted, Fasciola gigantica (the giant liver fluke) and Fasciolopsis buski (the giant intestinal fluke) have not been identified radiologically in man to our knowledge.

In patients with hepatic fascioliasis, CT reveals characterisitic changes in the liver. Nodular intrahepatic lesions with diminished attenuation, ranging in size from 4 to 10 mm but sometimes as large as 2 cm are seen (Figs. 21.28, 21.29). Intravenous contrast medium may help define these lesions on dynamic and delayed scans. These nodular lesions, which correspond to microabscess formation and can occur in clusters, cannot be differentiated from necrotic neoplasms or other abscesses. However, if peripheral (often subcapsular) tortuous lesions or channels are present (their reported incidence is 55-75%), hepatic fascioliasis becomes the primary consideration. These tortuous capsular channels have been seen also at surgery and laparoscopy and probably represent migratory tracts left by the flukes. With progressive disease, the flukes migrate toward the larger bile ducts, causing widespread coagulative necrosis or "liver rot". These lesions appear as cystic foci in the center of the liver. Thickening of the liver capsule (Figs. 21.28B, 21.29B) and subcapsular hematoma have also been reported as infrequent complications of hepatic migration of the flukes.

Fig. 21.28 A CT scan in a patient with fascioliasis shows multiple hypodense nodular lesions in the right lobe of the liver and tiny dot-like filling defects (small black arrows) within several dilated bile ducts which may represent flukes in the ducts. B CT scan at a lower level shows hypodense tortuous channels and nodular lesions in the periphery of the right lobe and slight ectasia of several ducts. There is contrast enhancement of a thickened liver capsule (arrowhead between ribs). These are typical CT findings in hepatic fascioliasis. (Courtesy of Dr. Joan Kendall.)

Fig. 21.29 Hepatic fascioliasis in a 33-year-old man with right upper quadrant pain, eosinophilia, and abnormal liver function tests. A bolus-phase CT scan reveals two 2- 3-cm low- attenuation nodules in the upper portion of the liver and tortuous peripheral lesions. Faint peripheral contrast enhancement of the lesions is seen (arrow). B The nodular lesions and channels have become isointense relative to the surrounding liver parenchyma during the equilibrium phase of the CT scan 17 min after bolus injection of contrast medium. However, enhancement of a thick liver capsule is now noted (arrow). An MRI study on this patient showed only one lesion as a poorly defined nodular area of increased signal intensity on T2-weighted images. (Courtesy of Dr. Bernard Van Beers, et al., Brussels and Radiology, 1990)

The above lesions regress or disappear after treatment. Often, the small cystic lesions calcify after treatment. CT is useful in follow-up of patients with fascioliasis to document response to therapy. Biliary duct dilatation and irregular wall thickening may be better demonstrated on ultrasound. The nonspecific round nodular lesions of hepatic fascioliasis can be visualized by ultrasonography as lesions of variable echogenicity and can also be identified on MRI scans. However, the characteristic tortuous channels have not been identified on ultrasonography or MRI to our knowledge and therefore CT is the preferred cross-sectional imaging modality for the hepatic form of this disease.