Types of Choledochal Cysts

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Home Different Types of Choledochal Cysts

If you or your child has just been told there is a choledochal cyst, one of the first things the medical team will want to establish is which type it is. That single label shapes almost everything that follows: which operation is offered, how much of the bile duct is removed, whether the liver is involved, and how closely things are watched for years afterwards. This page is the overview of the classification system — what the five types are, where each one sits in the biliary tree, how common each is, and what usually happens next. From here you can go deeper on any single type.

Why the type matters

Choledochal cysts are not really cysts in the everyday sense of fluid-filled sacs. They are abnormal widenings (dilatations) of the bile ducts — the plumbing that carries bile from the liver and gallbladder to the intestine. Because the ducts run both inside and outside the liver, a widening in one place is a very different problem from a widening in another.

A cyst confined to the duct outside the liver can usually be removed completely, and the bile flow rebuilt. A cyst that reaches up into the liver cannot simply be cut out, so the plan may involve removing part of the liver, long-term monitoring, or in some cases transplant assessment. The type also drives cancer surveillance. Bile duct cancer risk in choledochal cyst disease is estimated at roughly 5% overall, with some reviews reporting up to about 11%, and it typically appears in middle age — a median of around 49.5 years in the StatPearls review. That risk is not spread evenly across the types, which is exactly why classification is not just academic tidiness.

A short history: from three types to five

In 1959, Alonso-Lej and colleagues published the first workable system, dividing bile duct cysts into three types based on where the dilatation sat. It was a genuine advance, but it left out cysts inside the liver entirely.

In 1977, Todani and colleagues revised it into the five-type system still used worldwide today, adding the combined intrahepatic-and-extrahepatic pattern (type IV) and intrahepatic disease (type V, Caroli disease). Later refinements added subtypes — Ia, Ib and Ic for the shape and extent of the common bile duct cyst, and IVa and IVb depending on whether the liver ducts are involved. Some authors have since proposed further additions, including a type VI. The core Todani framework, however, is what your surgeon or radiologist will use.

The five types at a glance

Type I — common bile duct cyst. Dilatation of the bile duct outside the liver, either along its whole length or in one segment. The most common by a wide margin: reported at 50% to 80% of cases in clinical series and 80% to 90% in radiology sources. Usual treatment: complete excision of the extrahepatic duct with Roux-en-Y hepaticojejunostomy reconstruction.
Type II — diverticulum. A pouch budding off the side of the bile duct, with the duct itself otherwise normal. Rare, about 2% to 3% of cases. Usual treatment: removal of the pouch, sometimes with simple closure of its neck.
Type III — choledochocele. A bulge of the very last part of the bile duct into the wall of the duodenum. Around 1.4% to 4.5% of cases (Radiopaedia cites roughly 5%). Often managed endoscopically with sphincterotomy rather than open surgery, and carries the lowest cancer risk.
Type IV — multiple cysts. IVa involves ducts both inside and outside the liver; IVb involves multiple cysts outside the liver only. The second most common pattern, reported at 12% to 35% in clinical series, and more often seen in adults.
Type V — Caroli disease. Cystic dilatation of the bile ducts inside the liver, with the ducts outside the liver normal. Managed with infection control, segmental liver resection for one-sided disease, or transplant when both lobes are affected.

A closer look at each type

Type I

Type I is the classic choledochal cyst — a balloon-like or cigar-shaped widening of the common bile duct. Subtype Ia is cystic dilatation of the whole extrahepatic duct, Ib is a focal, segmental dilatation, and Ic is a smooth fusiform (spindle-shaped) widening. Children more often present with jaundice or a mass; adults more often with pain. Because the cyst lining carries the highest cancer risk of any type — accounting for around 68% of cyst-related cancers in one review — the whole duct is removed rather than simply drained. Read more on type I choledochal cysts.

Type II

Type II is a true diverticulum: a saccular outpouching on a stalk. It is genuinely rare and often found incidentally. Because the rest of the duct is normal, treatment can sometimes be as simple as excising the pouch and closing its neck, though a wide-based one may need fuller reconstruction. Read more on type II choledochal cysts.

Type III

A choledochocele sits at the junction where the bile duct enters the duodenum, and it often behaves more like a pancreatic or duodenal problem than a bile duct one — pancreatitis is a common presentation. Many are treated endoscopically. Read more on type III choledochal cysts, or choledochocele.

Type IV

Type IVa is the one that changes surgical planning most, because the disease extends into the liver. Surgery removes the extrahepatic portion and reconstructs bile flow, and partial hepatectomy may be added when one part of the liver is badly affected. Follow-up is lifelong. Read more on type IV choledochal cysts.

Type V (Caroli disease)

Here the dilatation is inside the liver. Caroli disease means the duct changes alone. Caroli syndrome means the same duct changes plus congenital hepatic fibrosis — scarring that can lead to portal hypertension — and it is linked to the PKHD1 gene and autosomal recessive polycystic kidney disease. That distinction matters: isolated Caroli disease is estimated at around 1 in 1,000,000 people, while Caroli syndrome is considerably more common, and the syndrome brings liver and kidney issues the disease alone does not. Cholangiocarcinoma risk is around 7%, and annual MRCP surveillance is commonly advised. Read more on type V choledochal cysts and Caroli disease.

The proposed type VI

Some authors describe isolated cystic dilatation of the cystic duct — the short duct connecting the gallbladder — as a type VI cyst. It is important to be clear: this is not part of the standard Todani classification. Todani’s system does not include it as a separate entity, and fewer than about twenty cases had been reported worldwide as of a 2017 literature review. Treatment is generally cholecystectomy with excision of the dilated duct. If you see type VI in a report, it is a descriptive label, not an established category.

Where the classification falls short

Clinicians have criticised the Todani system for years, and it helps to know why. The clearest issue is the overlap between type I and type IVa. One influential analysis found that essentially all type I cysts showed some degree of intrahepatic dilatation, making the boundary between the two look arbitrary — and since some intrahepatic widening can resolve once the downstream obstruction is fixed, the label can change after surgery.

A second debate is whether Caroli disease belongs in the system at all. Many authors argue that Caroli disease (a ductal plate malformation) and choledochocele (arguably a duodenal or sphincter problem) are distinct diseases that happen to produce duct dilatation, and sit awkwardly alongside true choledochal cysts. Cases that fit no category — cystic duct cysts, confluence cysts, mixed patterns — add to the pressure for revision. Newer classifications have been proposed, but Todani remains the shared language in practice.

How a type is assigned from imaging

Typing is done by picture, not blood test. Ultrasound is usually first, with reported sensitivity of about 71% to 97%, and it is often what finds the cyst, sometimes even before birth. MRCP (magnetic resonance cholangiopancreatography) is considered the gold standard for classification, with 90% to 100% sensitivity, because it maps the whole duct tree without radiation and can show an anomalous pancreaticobiliary junction. CT cholangiography (around 90% sensitivity) helps define intrahepatic involvement in types IV and V. ERCP gives the most detailed pictures but carries risks including pancreatitis, so it is used selectively. A cholangiogram taken during surgery can confirm or revise the type. Our diagnosis page walks through each test in detail.

Questions worth asking about your type

Which Todani type and subtype am I, or is my child? Ask for it in writing.
What imaging was it based on, and has MRCP been done?
Are the ducts inside the liver involved? This is the type I versus IVa question.
Does the type change the operation being recommended?
What is my long-term surveillance plan, and how often?
Was an anomalous pancreaticobiliary junction seen?

Type IV cysts are markedly more common in people diagnosed later in life — see choledochal cysts in adults. Understanding the type is a good foundation, but it is only part of the picture. You may also want to read about symptoms of choledochal cysts, the surgical treatment options, and the possible complications. Our frequently asked questions covers the things people ask most in the first weeks, and if you would like to talk to others who have been through it, please find our community.

Please note: this page is general information written for patients and families, not medical advice. Figures quoted come from published medical literature and differ between studies and populations. Always discuss your own or your child’s situation with a qualified hepatobiliary specialist — our guide to finding a doctor may help.