Choledochal Cyst
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Direct answer
A choledochal cyst is a congenital dilation of the biliary tract classified by Todani into five types: type I fusiform or saccular extrahepatic disease (the great majority), type II diverticulum, type III choledochocele, type IVa combined extra- and intrahepatic, and type V Caroli disease. Children present with the triad of abdominal pain, jaundice and a right upper quadrant mass; adults more often have recurrent cholangitis or pancreatitis. MRCP is the diagnostic study and demonstrates the anomalous pancreaticobiliary junction — a long common channel above 15 mm — whose reflux of pancreatic juice underlies the cholangiocarcinoma risk. Types I and IVa need complete cyst excision with Roux-en-Y hepaticojejunostomy; choledochoceles are managed endoscopically, and Caroli disease may need resection or transplantation.
What you must remember
- Todani mapping: I extrahepatic fusiform/saccular (commonest), II diverticulum, III choledochocele, IVa extra- plus intrahepatic, IVb multiple extrahepatic (rare), V Caroli intrahepatic disease.
- Long common channel: pancreaticobiliary junction longer than about 15 mm allows pancreatic enzyme reflux, stasis and inflammation — the accepted mechanism linking cysts to cholangiocarcinoma.
- Cancer risk: cholangiocarcinoma develops in a meaningful fraction of unresected cysts, rising steeply with age at operation — the argument for complete excision rather than drainage.
- Caroli signatures: type V disease shows segmental saccular intrahepatic dilations, the "central dot sign" on CT, recurrent cholangitis, autosomal recessive inheritance and association with autosomal dominant polycystic kidney disease.
- Presentation by age: children with pain, jaundice and a palpable mass; adults with cholangitis, pancreatitis, or an incidental finding; a handful present with cyst rupture or biliary colic from stones.
- Investigation ladder: MRCP for anatomy, MRCP or CT for the distal duct and pancreaticobiliary junction, liver function tests, and in suspicious cases brushings or PET where cancer is suspected.
- Operation for I and IVa: complete extramucosal cyst excision to the level of healthy duct, cholecystectomy, and Roux-en-Y hepaticojejunostomy; intrahepatic extension limits how much can be removed.
- Abandoned operation: cystenterostomy (internal drainage of the cyst without excision) is obsolete precisely because the retained cyst mucosa keeps its malignant potential.
Why the cyst must come out whole
The logic of excision is mucosal. The cyst wall is chronically inflamed, metaplastic epithelium bathed in refluxed pancreatic juice; draining the cyst relieves the jaundice of the moment but leaves the metaplastic mucosa in situ, and cholangiocarcinoma rates in patients drained rather than excised — reported in the range of one in ten or more, climbing with decades of follow-up and with older age at surgery — are the reason every modern algorithm mandates excision. Operatively, the cyst is mobilised circumferentially; the dissection stays close to the wall in the upper third but must avoid the pancreatic duct below, where the cyst funnels into the narrow distal duct near the pancreaticobiliary junction. The gallbladder goes with the specimen, since stones and inflammation travel with the disease. The proximal duct is divided where it calibres to normal, and a Roux-en-Y hepaticojejunostomy restores biliary continuity away from the pancreas. In type IVa disease the extrahepatic component is excised and the intrahepatic dilation surveyed lifelong; in Caroli disease confined to one lobe, segmentectomy can be curative, and diffuse bilateral disease with failing liver function ends at transplantation.
How exams frame Todani
Expect the classification question as a one-liner (type III is the choledochocele) and then the management question that separates rote learners from clinicians: "internal drainage versus excision" — the answer is always excision, because drainage preserves the malignant mucosa. The second favourite is the adult who has had "attacks of pancreatitis since childhood" with a soft right upper quadrant mass: choledochal cyst with pancreaticobiliary reflux, not idiopathic pancreatitis. Third, Caroli disease is examined as a medical entity — recurrent cholangitis, central dot sign, polycystic kidney association, and the calculus risk of intrahepatic stones — with surgery reserved for localised disease. Fourth, remember the paediatric differentials: a right upper quadrant mass with jaundice in a child includes choledochal cyst, hepatoblastoma and hydatid disease in the Indian setting, and MRCP arbitrates. Finally, know the complication list that completes any long-answer: pancreatitis, cholangitis, stones, cirrhosis from longstanding obstruction, rupture, and cholangiocarcinoma.
Frequently asked questions
Which is the commonest Todani type of choledochal cyst?
Type I — fusiform or saccular dilation of the extrahepatic bile duct — accounting for the great majority of cases.
Why must the cyst be excised rather than drained?
Retained cyst mucosa is metaplastic and chronically exposed to refluxed pancreatic juice, carrying a substantial and age-dependent risk of cholangiocarcinoma.
What is a choledochocele and how is it treated?
A Todani type III cystic dilation of the terminal common bile duct prolapsing into the duodenum, commonly managed by endoscopic sphincterotomy.
Which investigation defines choledochal cyst anatomy best?
MRCP, which demonstrates the cyst, the intrahepatic ducts and the anomalous pancreaticobiliary junction non-invasively.
What is Caroli disease?
Todani type V — congenital segmental saccular dilation of intrahepatic bile ducts with recurrent cholangitis, the central dot sign on imaging, and association with polycystic kidney disease.