Multiple biliary hamartomas

Multiple biliary hamartomas (MBH) are a rare cause of multiple benign hepatic lesions. The condition is also known as von Meyenburg complexes, multiple bile duct hamartomas and biliary microhamartomas. MBH is asymptomatic and usually found incidentally, where it is important to differentiate from other causes of multiple liver lesions, particularly metastases.

Epidemiology

The prevelance of MBH is ~ 3% at autopsy ¹ however prevalence on imaging is <1% as most hamartomas are < 5 mm in size and often not detected. MBH is reportedly three times more common in women than men ².

Pathology

Biliary hamartomas are composed of small disorganised clusters of dilated cystic bile ducts lined by a single layer of cuboidal cells and surrounded by an abundant fibrocollagenous stroma ^1,6-7. Although they may communicate with the biliary tree, they generally do not. They are thought to arise from embryonic bile duct remnants that have failed to involute.

Associations

MBH is known to be associated with 

• autosomal dominant polycystic kidney disease (ADPKD) ³ 
• polycystic liver disease ³. 

Several case reports have identified possible malignant transformation of biliary hamartomas into cholangiocarcinoma ⁴, and hepatocellular carcinoma ⁵.

Radiographic features

Multiple small round or irregular lesions throughout the liver, with some predilection for subcapsular regions ¹. Usually 5 - 30mm in size when detected by imaging (however most lesions are < 5mm when detected by pathologists). Radiographic findings can be non-specific and may be hard to differentiate from metastases and micro-abscesses.

Ultrasound

Small hamartomas are usually echogenic if discreetly seen. Often tiny individual hamartomas cannot be resolved and are instead interpreted as diffuse heterogenous liver echotexture. Larger hamartomas (> 10 mm) may appear hypoechoic or anechoic and comet tail artifact may be seen ⁸.  Appearances mimic metastases (see ultrasound appearances of liver metastases). 

CT

Biliary hamartomas are hypoattenuating and often show no enhancement ⁶. Occasionally an enhancing nodule or rim may be identified in a small number of lesions. 

Angiography

Only a small number of the many lesions that are actually present can be seen as grape-like clusters of abnormal vascularity with contrast persisting into the venous phase ⁹.

MRI 

Most biliary hamartomas are :

• T1 : hyperintense compared to liver parenchyma
• T2
  • hyperintense
  • depending on TE, may approach that of CSF
• T1 C+ (Gd)
  • usually no enhancement
  • thin peripheral rim enhancement has been described (see below) - this may represent compressed normal liver parenchyma ^13-14

However, in ~ 90% of cases an occasional hamartoma can be found containing a nodule or rim that is T1 isodense and T2 intermediate, of which ~ 90% will enhance. Hamartomas show no diffusion restriction on DWI sequences. ^2,8,10

Nuclear medicine

^99mTc-DISIDA scan shows delayed uptake and delayed emptying of tracer within larger biliary hamartomas.¹¹

Treatment and prognosis

Aside from the possible risk of malignant transformation (see associations earlier), MBH is a benign asymptomatic condition with no long-term consequences and no treatment is required.

Etymology

It is named after Hans von Meyenburg who was a pathologist born in Dresden in 1887 and was the first to describe the pathology of biliary hamartomas in an article published in 1918 ¹². Biliary hamartomas to this day remain frequently referred to as von Meyenburg complexes.

Differential diagnosis

General imaging differential considerations include

• multiple liver metastases : more variable size and prominent enhancement
• mutliple liver microabscesses : clinical context is important, may have diffusion restriction on MRI
• multiple small hepatic cysts