Mass-forming intrahepatic cholangiocarcinoma

Mass-forming intrahepatic cholangiocarcinomas (MF-ICC), also referred as peripheral cholangiocarcinomas, comprise one of the three recognized growth patterns of intrahepatic cholangiocarcinomas. 

On imaging, these tumors usually present as large and relatively well-defined hepatic masses with lobulated margins and showing peripheral rim enhancement. They are often associated with peripheral biliary dilatation. 

Epidemiology

Mass-forming intrahepatic cholangiocarcinomas are associated with chronic liver diseases, including viral hepatitis ⁵. 

Clinical presentation

These tumors tend to present late as larger masses as they rarely cause symptoms when smaller, early in their natural history ⁴. 

Pathology

The mass-forming subtype is the most common among the intrahepatic cholangiocarcinomas ⁴.

Etiology

Mass-forming tumors mostly originate from cholangiocarcinomas in the peripheral small bile ducts and, rarely, from a mixed presentation of large duct cholangiocarcinomas with both periductal and mass-forming lesions ⁵. 

Macroscopic appearance 

Peripheral cholangiocarcinomas are commonly large white tumors with dense fibrosis ⁴.

Genetics

Reported mutations associated with mass-forming cholangiocarcinoma include KRAS, TP53, DH1/2, FGFR2 fusions, BAP1, BRAF, ARID1A, SMAD4, and IDH1 ⁸.

Radiographic features

General morphological features that commonly guide radiologists to the diagnosis of mass-forming intrahepatic cholangiocarcinoma are the associated capsular retraction and distal bile duct dilatation.

The enhancement pattern seen on post-contrast dynamic images can be quite variable, depending on tumor size and degree of differentiation. Be aware that enhancement features of mass-forming intrahepatic cholangiocarcinoma and hepatocellular carcinomas can overlap when tumors are smaller than 3 cm and in cirrhotic livers ⁷. 

Ultrasound

These tumors present as a homogeneous and well-delineated liver mass, which commonly has intermediate echogenicity and irregular contours. Other features may include: 

• peripheral hypoechoic halo of compressed liver parenchyma
• often associated with capsular retraction ¹ 
• dilated bile ducts distal to the mass 

CT

Mass-forming cholangiocarcinomas are relatively well-defined and markedly hypodense on the non-contrast studies. On dynamic post-contrast scans:

• there is minor peripheral rim enhancement during both the arterial and portal venous phases
  • arterial enhancement has been associated with better prognosis ⁶
• the central part of the tumor usually does not enhance during the early phases, but frequently show gradual centripetal prolonged enhancement at delayed-phases ^1,2,4
• rate and extent of enhancement depend on the degree of central fibrosis ¹ 

The bile ducts distal to the mass are typically dilated.

Again, capsular retraction may be evident and is highly suggestive of this etiology. Lobar or segmental hepatic atrophy is usually associated with vascular invasion ³. 

Although narrowing of the portal veins (or less frequently, hepatic veins) is seen, unlike hepatocellular carcinoma, cholangiocarcinoma only rarely forms a tumor thrombus ¹.

MRI​

• T1: hypointense ⁷
• T2: hyperintense ⁷
• DWI: target sign of diffusion restriction at high b values
  • central dark area on DWI may represent fibrosis and necrosis ⁷​
  • this appearance, although not specific and only seen in less than 50% of cases, helps in distinguishing the mass from a hepatocellular carcinoma
• T1 C+ (Primovist)
  • pattern and intensity of enhancement has been associated with tumor differentiation and, therefore, prognosis ⁶
    • hypoenhancement reflects poor differentiation 
    • rim enhancement reflects intermediate differentiation 
    • diffuse enhancement reflects a well-differentiated tumor

Differential diagnosis

For a mass-forming intrahepatic cholangiocarcinoma consider:

• hepatocellular carcinoma (HCC)
  • may appear very similar, particularly in tumors smaller than 3 cm and in a cirrhotic liver ⁷
  • intralesional fat
  • diffuse hyperintensity on unenhanced T1 weighted imaging
  • nodule-in-nodule appearance
  • capsular enhancement in the portal and delayed phases 
  • tumor thrombus
  • capsular retraction is uncommon
• liver metastases
  • central necrosis (high T2 signal) is more common
  • multiplicity is more common 
• other primary liver tumors