Does hyperamylasemia in choledochal cyst indicate true pancreatitis? An experimental study.

Patients with choledochal cyst often have repeated attacks of abdominal pain accompanied by hyperamylasemia, and they may be diagnosed as having acute pancreatitis. However, the attacks generally tend to subside in a short period by conservative treatment, and evidence of pancreatitis is rarely observed at the time of surgery. Choledochal cyst is commonly associated with pancreatobiliary maljunction, and high concentrations of pancreatic enzymes in bile are usually observed. When the bile duct pressure increases due to obstructive cholangitis, pancreatic enzymes in bile may regurgitate into the blood stream. Cholangiovenous reflux of amylase might cause hyperamylasemia. In order to investigate the mechanism of hyperamylasemia by cholangiovenous reflux, canine pancreatic juice or bile from a patient with choledochal cyst was injected into the obstructed common bile duct in dogs. The pancreatic enzymes in bile could readily enter into the blood stream at the pressure level of 15 mmHg or more in the bile duct. The peak amylase level in the thoracic lymph was observed to be more than 4 times higher than that in the blood serum, and the lymph flow during 30 minutes increased significantly from 8.1 to 20.4 ml at the bile duct pressure level of 20 mmHg. The reflux of amylase in bile into the blood stream via both the hepatic vein and thoracic duct might result in hyperamylasemia in the patients with choledochal cyst.