Choledochal cyst

Choledochal cysts represent congenital disproportionate cystic dilatations of the biliary tree. Diagnosis relies on the exclusion of other conditions as a cause of biliary duct dilatation: (i.e.  tumour, gallstone or inflammation as the cause).

Epidemiology

Choledochal cysts are rare, with an incidence of 1 : 100000 - 150000. Although they may be discovered at any age, 60% are diagnosed before the age of 10 years ¹.  There is a strong female predilection with a M : F ratio of 4 : 1. There is a greater prevalence in East Asia.

Clinical presentation

Classically presentation includes the triad of ¹:

• abdominal pain
• jaundice
• abdominal mass

This triad is however only present in 19 - 60% of cases, with palpable mass being the least common manifestation.

Pathology

Their aetiology is uncertain but a close association with anomalous formation of the pancreaticobiliary ductal junction is reported in some subtypes ¹.

Associations

A number of associations are recognised, including ¹:

• biliary atresia
• hepatic fibrosis
  • associated with type V (Caroli disease)

Classification

Commonly accepted classification currently is one devised by Todani et al. There are 5 main types, with several sub types some of which can be pathologically unrelated. Briefly :

• type I : most common, accounting for 80 - 90%¹ (this type can present in utero)
  • Ia : dilatation of extrahepatic bile duct (entire)
  • Ib : dilatation of extrahepatic bile duct (focal segment)
  • Ic : dilatation of the common bile duct portion of extrahepatic bile duct
• type II : true diverticulum from extra hepatic bile duct
• type III : dilatation of extra-hepatic bile duct within duodenal wall (choledochocoele)
• type IV : next most common
  • IVa : cysts involving both intra and extrahepatic ducts
  • IVb :  multiple dilatations / cysts of extra hepatic ducts only
• type V : multiple dilatations / cysts of intra hepatic ducts only (Caroli disease)

See : Todani classification of bile duct cysts. 

Radiographic features

Imaging of the biliary tree can be achieved with ultrasound, CT, direct contrast studies (ERCP, PTC) or MRI. 

Ultrasound

Key to the diagnosis is a dilated cystic lesion which communicates with the bile duct and is separate from the gall bladder. Careful search for other causes needs to also be undertaken (see differential below), remaining cognisant that both stone formation and malignancy are associated with choledochal cysts. 

CT and MRCP

Findings are similar to US, with a greater ability to demonstrate intrahepatic disease. It is important to remember that with CT IVC the contrast mixing in the cyst may be inhomogeneous. It does however have the advantage that it conclusively demonstrates communication with the biliary tree ¹.

Complications

The two most frequent complications of choledochal cysts are stone formation and malignancy. Complications include:

• stone formation: most common
• malignancy
  • cholangiocarcinoma
  • life time incidence 10 - 15% ⁵
• cyst may rupture leading to bile peritonitis
  • most frequently seen in neonates ¹
• pancreatitis

Treatment and prognosis

The only feasible treatment is surgical excision, with reconstruction. A number of possible approaches exist, depending on cyst location etc.. Typically a Roux-en-Y hepaticojejunostomy is performed ¹.

Differential diagnosis

• duodenal diverticulum
• pancreatic cystic lesions
  • pseudocyst(s)
  • cystic tumours
• other causes of biliary tree dilatation
  • impacted gallstone
  • cholangiocarcinoma
  • biliary stricture