Choledochal Cyst

Clinical The etiology of choledochal cysts is unknown. They are usually classified under congenital cystic biliary malformations, although neonatal viral infection or a bile duct wall abnormality may be responsible. In neonates and infants some authors label this condition simply as congenital biliary dilation. The borderline between a prominent but still normal caliber duct and a choledochal cyst is a matter of definition. A number of Western authors have commented on the rarity of choledochal cysts in their practices. These cysts are encountered more often in Asia, and most larger studies are from Asia. A relationship between choledochal cysts and congenital hepatic fibrosis has been speculated; some neonates with choledochal cysts also have periportal fibrosis. An inconsistent association exists between a choledochal cyst and intestinal malrotation. In some adults differentiation between primary chronic dilation leading to bile stasis and stone formation and secondary dilation due to biliary stones and resultant inflammation is not possible.
In 1959, Alonso-Lej et al. classified choledochal cysts into three types: I, fusiform dilation of a portion or entire extrahepatic bile duct system; II, saccular diverticular-like outpouching in extrahepatic ducts; and III, focal dilation of distal common bile duct segment (or common pancreatobiliary channel) within the wall of the duodenum. Type III is also called a choledochocele. Todani et al. expanded this system in 1977 to better reflect a surgical approach. The Todani modification subdivides type I cysts into Ia, aneurysmal dilation; Ib, segmental dilation; and Ic, diffuse, cylindrical dilation; and also includes type IV cysts: IVa, multiple intra- and extrahepatic duct cysts; and IVb, multiple extrahepatic cysts only. Also added was a type V: single or multiple intrahepatic duct cysts.
The most common type of choledochal cyst is type I. These cysts tend to be associated with biliary or sphincter of Oddi anomalies, and in these individuals reflux of pancreatic content with secondary bile duct wall inflammation and thinning appears to be a reasonable etiology for choledochal cyst formation.

This is radiology images of Type I choledochal cyst involving hepatic duct arrow).

A type II choledochal cyst is a rare congenital malformation. An occasional one presents as an adjacent tumor without an obvious bile duct communication; biliary communication presumably is obliterated due to inflammation. No strict criteria define a type III cyst (choledochocele), and some authors include dilation of a common channel as a type of choledochocele. Using a strict definition, however, a choledochocele is probably as rare as a type II cyst. These patients are prone to choledocholithiasis. Smaller choledochoceles tend to be asymptomatic.
Among adults with choledochal cysts treated in 17 institutions of the French Associations for Surgical Research, 50% had both extra- and intrahepatic bile duct dilation and thus a Todani type IVa choledochal cyst; of these, nine included segmental, left lobe duct involvement, and these patients required a combined left lobectomy and extrahepatic cyst excision.Biliary carcinoma was present in 12% of these tients.
Some authors label type V dilation of small intrahepatic radicals, as Caroli’s disease (discussed later).Whether Caroli’s disease is indeed a type of choledochal cyst is debatable. Acquired dilated ducts due to prior stone disease or infection are not considered to be choledochal cysts. Even then, not all dilated ducts fit the above classification. Is a focally dilated cystic duct a choledochal cyst? These cysts are a cause of prolonged neonatal jaundice. Others are detected in children. Only a rare choledochal cyst manifests during pregnancy. In some adults pancreatitis is their initial presentation. Their propensity to harbor a carcinoma needs to be considered when planning therapy.
The risk of biliary malignancy in a setting of a choledochal cyst increases with age, although cancers have developed in young patients. Bile stasis, irritation, possible mutagenicity of bile mixing with pancreatic secretions, and epithelial damage probably play a role in cancer development. Most tumors are adenocarcinomas but an occasional undifferentiated carcinoma, squamous cell carcinoma, or even adenoacanthoma is encountered. Gallbladder carcinomas have also been reported.
Imaging
In neonates and children, US reveals a choledochal cyst as a cystic structure in the region of the bile ducts. These dilated ducts often extend intrahepatically. The gallbladder ranges from normal in size to somewhat distended. Traditionally, ERCP has been used to detect and evaluate choledochal cysts in adults, but CT, US, MRI, or scintigraphy is a viable alternative. Imaging reveals a fluid-filled cystic structure. Both CT cholangiography and MRCP detect choledochal cysts with roughly similar image quality and provide information comparable to ERCP; CT cholangiography appears superior to MRCP in detecting any superimposed stones, but the latter also provides information about any associated anomalous pancreaticobiliary duct junction and does not require use a contrast agent. Currently, MRCP is the procedure of choice in evaluating these cysts.
A choledochocele (type III cyst) should be readily detected with MRCP or ERCP; the papilla of Vater bulges, suggesting a submucosal tumor. Their cystic nature is also apparent by endoscopic US. A carcinoma developing in a choledochal cyst is difficult to detect with imaging; at times a subtle focal or diffuse bile duct wall thickening suggests the diagnosis. These tumors enhance during arterial-phase CT, becoming isodense on delayed phases. Cholangiography reveals either an elevated, irregular outline, or a focal narrowing. Hepatobiliary cholescintigraphy in patients with choledochal cysts reveals about two thirds of gallbladders nonvisualizing; resected gallbladders in some of these patients do not show evidence of cholecystitis. The diagnostic accuracy of cholescintigraphy for cholecystitis is low in patients with a choledochal cyst.With partial obstruction, scintigraphy shows tracer activity within the cyst; in general, a choledochal cyst tends to fill with radiotracer later than expected and stays filled longer. Radionuclide accumulation in the cyst but no intestinal activity is a not uncommon finding.

This is radiology images of Choledochocele in an 85–year-old man. Contrastenhanced computed tomography (CT) reveals a dilated distal common bile duct indenting the descending duodenum (arrow). More superior images identified a dilated gallbladder. Surprisingly, the patient was not jaundiced.

Therapy
No curative therapy is possible with extensive intrahepatic involvement of both lobes, aside from liver transplantation. Some choledochoceles are treated by simple endoscopic unroofing. Nevertheless, because most choledochal cysts are premalignant, a simple drainage procedure is believed to be insufficient therapy in most patients. A malignancy has developed years after cystenterostomy. Cyst excision and a hepaticojejunostomy are traditional procedures of choice, with some surgeons preferring a hepaticoantrostomy. The latter anastomosis is believed to be associated with fewer episodes of recurrent cholangitis, although postoperative cholescintigraphy does not differ significantly between the two surgical procedures and thus differences in bile stasis and reflux presumably are not a cause of the more frequent recurrent cholangitis seen after hepaticojejunostomy. An anastomotic bile duct carcinoma is a rare complication. An unsuspected choledochal cyst is occasionally encountered during laparoscopic cholecystectomy; the underlying anatomy can be studied and a choledochocele diagnosed by either laparoscopic contact US or intraoperative cholangiography. Findings with Tc-00m-IDA scintigraphy are similar in infants after a Roux-en-Y hepaticojejunostomy and after a hepaticoantrostomy, although the former are more prone to develop recurrent cholangitis.

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