Figure 1: The patient is status post distal pancreatectomy and splenectomy. The extra-hepatic biliary tract and pancreatic duct anatomy are within normal limits. There are innumerable small high T2 lesions within the liver parenchyma.

Figure 2: Coronal T2-weighted images again demonstrate innumerable foci of high T2 signal in the liver parenchyma.

Figure 3: Post-contrast image VIBE image demonstrates that the lesions are non-enhancing.

Bile duct hamartomas (von Meyenburg complexes).

Hepatic bile duct hamartomas (von Meyenburg complexes) are benign biliary malformations which are currently considered part of the spectrum of fibropolycystic diseases of the liver. They originate from embryonic bile ducts that fail to involute. Biliary hamartomas are common and estimated to be present in approximately 30% of patients. They are most often multiple, small lesions (almost always < 1 cm in diameter), and are generally without clinical manifestations. These hamartomas are usually encountered as incidental findings at imaging, laparotomy, or autopsy. They can occur in association with underlying fibrocystic disease of the liver, such as polycystic liver disease, congenital hepatic fibrosis, and Caroli's disease.

The significance of these biliary hamartomas lies in the possibility of these lesions being mistaken for more serious lesions, such as, metastatic carcinoma. Histologic studies can clarify the benign nature of the tumor and establish the correct diagnosis. The characteristic features of biliary hamartomas include small, sometimes dilated, irregular, and branching bile ducts and ductules lined by well-differentiated, cuboidal columnar epithelium, embedded in an extensive fibrous stroma. In general, biliary hamartomas contain no or few vascular channels. These benign tumors can be solitary or multiple, and multiple tumors can be extensive, as seen in this case. There is no risk of malignant degeneration, and extensive hepatic resection or transplantation is not indicated.

On MR images, biliary hamartomas are small (usually less than 1 cm) and well defined. All lesions are hypointense relative to the liver on T1-weighted images. In general, they show negligible enhancement on early and late post-gadolinium images. Although their appearance resembles simple cysts, biliary hamartomas can demonstrate a thin rim of enhancement on early and late post-contrast images. This ring enhancement often lends to a misdiagnosis of these lesions as metastases. The thin enhancing rim of biliary hamartomas can be correlated histopathologically to the compressed hepatic parenchyma bordering the lesion. In contrast, the pattern of ring enhancement displayed by metastases relates histopathologically with the outer, most vascularized portion of the tumor. MR imaging further corroborates the different histologic profiles of the two process through the observation that enhancement in biliary hamartomas does not progress centrally, where as enhancement in metastases most often progresses centrally. With MR cholangiography, biliary hamartomas appear as multiple tiny cystic lesions that do not communicate with the biliary tree.

References:

1. Semelka RC. Abdominal-Pelvic MRI. New York: Wiley-Liss Inc, c2002. pp. 53-54.
2. Mortele KJ and Ros PR. Cystic Focal Liver Lesions in the Adult: Differential CT and MR Imaging Features. Radiographics. 2001; 21: 895-910.