Cholangiocarcinoma

Cholangiocarcinoma is a malignant tumour arising from the biliary tree, and tends to have a poor prognosis and high morbidity. It is the second most common primary hepatic tumour, with intra-hepatic cholangiocarcinomas accounting for 10-20% of primary liver tumours.

Epidemiology

Although overall cholangiocarcinoma is rare, there are significant variations in incidence according to region, with much higher rates seen in Southeast Asia ².

Incidence is usually in the elderly (7^th decade) ⁷. There may be a slight male predilection. 

Risk factors

A number of risk factors for cholangiocarcinoma have been identified including ^1-2:

• primary sclerosing cholangitis (PSC):
  • major risk factor in western countries
• recurrent pyogenic cholangitis (hepatolithiasis):
  • major risk factor in endemic areas
• Asian liver flukes:
  • Opisthorchis viverrini
  • Clonorchis sinensis (clonorchiasis)
• Caroli's disease/choledochal cysts:
  • lifetime risk of 10-15% ²
• toxins:
  • thorotrast
  • dioxin
  • polyvinyl chloride
  • heavy alcohol use
• viral infection(s):
  • HIV
  • hepatitis B and hepatitis C
  • EBV

Clinical presentation

Typically the presentation is with painless jaundice.

Pathology

Macroscopically cholangiocarcinomas have a number of different growth patterns (see below) and their macroscopic appearance will reflect this. In general they are sclerotic masses without haemorrhage or macroscopic necrosis ².

Histologically, cholangiocarcinomas are divided into well, moderately and poorly differentiated adenocarcinomas ². In specimens of bile ducts from patients with hepatolithiasis, biliary intraepithelial neoplasia (BilIN) is common finding and is considered to be a precursor lesion of cholangiocarcinoma. It is typically a microscopic lesion with a flat or micropapillary dysplastic epithelium. It is synonymous with carcinoma in situ ².

In general the active tumour is at the periphery, with the central portions having been replaced by fibrosis, accounting for the capsular retraction which may be seen in intrahepatic tumours.

Growth patterns/types

Cholangiocarcinomas can be either intra or extrahepatic. They are also classified according to macroscopic growth pattern ²:

• intra hepatic:
  • mass-forming
  • periductal infiltrating: most common at the hilum
  • intraductal: slow growing with better prognosis
• extra hepatic:
  • nodular
  • sclerosing
  • papillary

Alternatively intrahepatic tumours can be divided into ³:

1. peripheral:
   • distal to the secondary bifurcation of left or right hepatic duct
   • typically mass-forming
2. hilar (Klatskin tumour):
   • typically periductal infiltrating

Mass-forming

Intrahepatic (peripheral) tumours are most commonly of the mass-forming type ³. They demonstrate variable amounts of central fibrosis, usually marked.

Periductal infiltrating

Periductal infiltrating intrahepatic tumours are most common at the hilum, where they are known as Klatskin tumours ³, but can be seen in combination with mass forming tumours within the liver. Growth along the walls of the duct may narrow or dilate the duct. 

Intraductal

Intraductal tumours make up 8-18% of resected cholangiocarcinomas ³ and a much smaller number of all cholangiocarcinomas (as most are inoperable). They are characterised by alterations in duct calibre, usually ductectasia with or without a visible mass. If a mass is visible it may be mural or polypoid in shape ². The duct dilatation is thought to be due to abundant mucin production. This entity is thought to be similar to the pancreatic IPMN.

Extrahepatic/large duct

There is much confusion in the literature as to the definition or extrahepatic cholangiocarcinomas, and there is thus some overlap.

In terms of the distribution of large duct (hilar and extrahepatic) tumours ³:

• intrahepatic large ducts: 15%
• hilum/proximal third of CBD: 50%
• middle third CBD: 17%
• distal third CBD: 18%

These tumours are most commonly infiltrating, although both exophytic (mass-forming) and polypoid (intraductal) types are identified. They have similar appearances to their intrahepatic counterparts ³. 

Staging

Traditionally the Bismuth-Corlette classification was used to asses resectability, however with modern aggressive resection strategies, it is of little help, as intrahepatic tumours can also be tackled ⁵.

Important features in modern assessment include ⁶: 

• tumour size (>3cm;3 cm)
• lymph node involvement
• multiple lesions
• extent of biliary tree involvement
• vascular invasion

Radiographic features

Ultrasound

The appearance will vary according to the growth pattern. 

Mass-forming intrahepatic: tumours will be homogeneous mass of intermediate echogenicity with a peripheral hypoechoic halo of compressed liver. They tend to be well delineated but irregular in outline, and are often associated with capsular retraction ², which if present is helpful in distinguishing cholangiocarcinomas from other hepatic tumours.

Periductal infiltrating intrahepatic: tumours typically are associated with altered calibre bile duct (narrowed or dilated) without a well-defined mass.

Intraductal: tumours are characterised by alterations in duct calibre, usually ductectasia with or without a visible mass. If a polypoid mass is seen, it is usually hyperechoic compared to surrounding liver ².

CT

Mass-forming cholangiocarcinomas: are typically homogeneously low in attenuation on non-contrast scans, and demonstrate heterogeneous minor peripheral enhancement with gradual enhancement centrally ^2-3. The rate and extent of enhancement depends on the degree of central fibrosis ².  Again, capsular retraction may be evident. The bile ducts distal to the mass are typically dilated.

Although narrowing of the portal veins - or less frequently hepatic veins - is seen, unlike HCC, cholangiocarcinoma only rarely forms a tumour thrombus ².

Lobar or segmental hepatic atrophy is usually associated with vascular invasion ⁶. 

Periductal infiltrating: intra-hepatic tumours appear as regions of thickening of the periductal parenchyma with altered calibre of the involved duct (narrowed or dilated). These are most common at the hepatic hilum. There is usually some distal dilatation of the biliary tree.

Intraductal tumours: are characterised by alterations in duct calibre, usually ductectasia with or without a visible mass. If a polypoid mass is seen it is hypoattenuating on pre-contrast imaging, and demonstrates enhancement ².

MRI/MRCP

Appearances on MR are similar to those described above on CT, except that MR is more sensitive to contrast enhancement ³.

Direct cholangiography

Direct cholangiography is a blanket term for any imaging obtained with intra-biliary tree contrast, and includes:

• PTC
• ERCP
• CT IVC
• MRCP

All these modalities not only allow evaluation of the the biliary tree, but are invaluable in planning treatment as assessing for resectability.

Treatment and prognosis

The most important factor in prognosis is whether or not the tumour is able to be resected. Even with resection, prognosis is poor with 5 year survival of only 10-44% ⁴.

Pattern of metastatic spread include ¹:

• intrahepatic vascular involvement with numerous local metastases. 
• regional lymphnodes (50% at autopsy)
• haematogenous (50% at autopsy):
  • lungs
  • bones, especially vertebrae
  • adrenals
  • brain

Differential diagnosis

Differential diagnosis is different according to whether the tumour is intra or extrahepatic and depending on the growth pattern.

For an intra-hepatic mass-forming cholangiocarcinoma consider:

• liver metastases:
  • central necrosis (high T2 signal) is more common
• hepatocellular carcinoma (HCC):
  • tumour thrombus more common
  • capsular retraction uncommon
  • may appear very similar
• other primary liver tumours
• hepatic abscess

For a peri-ductal infiltrating cholangiocarcinoma consider:

• benign stricture:
  • usually short-segment 
  • regular margin
  • symmetric narrowing
  • no ductal enhancement
  • no lymph node enlargement
  • no periductal soft-tissue mass
• periportal lymphangitic metastasis ²

For an intra-ductal cholangiocarcinoma consider:

• intraductal invasion by a HCC:
  • extra-ductal mass
• hepatolithiasis:
  • no enhancement
  • higher attenuation
• biliary cystadenoma or cystadenocarcinoma:
  • intra-tumoural cysts do not communicate with the biliary tree
• benign stricture