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KK Women's and Children's Hospital 229899 Singapore
The sensitivity of sonography in detecting the rupture of a choledochal cyst may be limited by the presence of bowel gas and the small size of the collapsed cyst. CT is sometimes useful when the sonogram is nondiagnostic.
A 6-month-old girl was admitted for vomiting, poor feeding, and lethargy. She had a high spiking fever and increasing abdominal distention.
The initial abdominal radiograph showed ascites. Sonography confirmed this and also revealed low-level echoes in the ascitic fluid. The intrahepatic bile ducts were healthy, but the extrahepatic bile ducts were obscured by gas in the overlying bowel. A CT scan was subsequently obtained and revealed a dilated common bile duct with its largest diameter (1 cm) at the level of the pancreatic head. The common bile duct had a crinkled appearance (Fig. 2A), and a defect was present in its posteromedial aspect (Fig. 2B). Periductal fluid was shown in the pancreatic head (Fig. 2C).
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At surgery, 200 mL of bile-stained ascitic fluid was found, caused by a ruptured type 1 choledochal cyst. The site of perforation was the posterior aspect of the common bile duct and was 2 mm wide. No anomalous biliary ductal system was identified. The cyst was excised with the gallbladder and a hepaticojejunostomy created. Histologic workup revealed extensive fibrous replacement of the muscle coat and necrosis of all layers of the wall in the vicinity of the perforation.
The incidence of choledochal cyst rupture is small, but serious complications such as septic shock may result. Yamaguchi [1] analyzed the Japanese language literature covering 1433 patients with choledochal cysts and found bile peritonitis caused by perforation of a choledochal cyst in 26 patients (1.8%). The male–female ratio was 1:3.8. Ages ranged from 10 days to 15 years (average, 3 years).
The cause of choledochal cyst rupture is often unknown; several causes have been proposed. These include trauma, raised intraabdominal pressure caused by vomiting, distal ductal obstruction by protein plugs, pregnancy, and continuous reflux of pancreatic juice into the cyst [2].
Preoperative diagnosis of a ruptured choledochal cyst is difficult. A study of 13 patients by Ando et al. [3] showed that the diagnosis was made before surgery in only five patients (38%). Detection of a ruptured choledochal cyst may be difficult even during laparotomy because it may rupture posteriorly, is often not suspected, and is small after it collapses [4].
To our knowledge, the CT features of a ruptured choledochal cyst have not been reported. In our patient, CT revealed dilatation of the common bile duct, which is a feature of a type 1 choledochal cyst. The perforation was well shown on CT as a posteromedial defect in the common bile duct. Periductal fluid appearing as a double channel indicates the presence of a nearby perforation. The crinkled appearance of the collapsed choledochal cyst can be explained by relief of tension after the cyst rupture.
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