Gastrointestinal ImagingHamartoma, biliary
(also called von Meyenburgh complex),
benign malformations of the intrahepatic bile ducts composed microscopically by
focal disorderly collections of dilated branching tortuous bile ducts, set in a dense fibrocollagenous stroma. These bile ducts are lined by a single layered cuboidal epithelium and may contain pink amorphous material or bile plugs. Extreme ductal dilatation may lead to the formation of cyst-like structures that are large enough to be seen macroscopically. Luminal communication between the hamartomas and genuine, draining biliary system is controversial.
Grossly they appear as greyish-white or green nodules of a size between 0.1 and 0.5 cm in diameter, but occasionally aggregates of 1 cm or even larger are possible. Biliary hamartomas are rarely solitary. Most commonly, multiple lesions scattered throughout the liver are apparent. They are typically well circumscribed but are not encapsulated. The incidence of this malformation has been reported as 2.8% on microscopic evaluation and as 0.69% on macroscopic study.
The pathogenesis is unknown but an association with congenital hepatic fibrosis and polycystic liver disease is suggested. A few cases associated with cholangiocarcinoma have been reported but it is generally assumed that neoplastic transformation of these hamartomas does not occur. Pathological correlation has shown that lesions visualized by radiological imaging represents either a single hamartoma or an aggregate of multiple tiny hamartomas.
The ultrasound appearance of biliary hamartomas has been reported as either hypoechoic or hyperechoic (Fig.1a) and even mixed hypo- and hyperechoic.
On CT (Fig. 1b), biliary hamartomas are typically depicted as multiple, round small hypoattenuating and nonenhancing areas distributed throughout the liver without a distinctive distribution pattern. With increasing use of spiral CT and the ability for thin collimation and short reconstruction interval it can be assumed that more and more of these hamartomas will be visualized. They pose differential diagnostic problems with multiple small liver metastases especially in oncological patients. They can be distinguished more easily from intrahepatic dilated bile ducts by the absence of a tubular branching pattern.
On MRI the lesions are hypointense on T1-weighted images and hyperintense on T2-weighted images. On heavily T2-weighted images with longer echotime the signal intensity of the lesions remains high allowing a differentiation with liver metastasis.
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a. Ultrasound examination. Note the subtle hyperechoic multinodular (arrowheads) appearance of the liver.
b. CT following intravenous contrast medium administration. Note the innumerable small, round, nonenhancing structures, distributed throughout the liver without a distinctive pattern.
Reprinted from: L.M. Swinnen et al. Multiple bile duct hamartomas simulating liver metastases on US and CT. Eur Rad 1995;5:58, by courtesy of the Publisher of Eur Rad.
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Hamartoma, biliary, Fig.1 (a) | | Hamartoma, biliary, Fig.1 (b) | |