Autoimmune Dorsal Pancreatitis: Involvement of the Pancreatic and Bile Ducts in Autoimmune Pancreatitis

Abstract

Background and Aim: Typical cases of autoimmune pancreatitis (AIP) show a diffusely enlarged pancreas with a sausage-like appearance and diffuse irregular narrowing of the entire main pancreatic duct. A focal type of AIP, showing focal swelling with localized narrowing of the main pancreatic duct and upstream dilatation, is regarded as a variant of AIP. Stenosis of the bile duct frequently occurs with AIP. We examined the involvement of the pancreatic and bile ducts in patients with AIP, and proposed a new term of autoimmune dorsal pancreatitis. Patients and Methods: Clinical and cholangiopancreatographic findings of 32 patients (26 men and 6 women, average age 68.4) with AIP were evaluated. For the purposes of this study, the pancreatic duct system was divided into 3 portions: the ventral pancreatic duct, the head portion of the dorsal pancreatic duct, and the body and tail of the dorsal pancreatic duct. Results: Both the ventral and dorsal pancreatic ducts were involved in 27 patients, while in 5 patients only the dorsal pancreatic duct was involved. Segmental narrowing of the head of the dorsal pancreatic duct with normal ventral pancreatic duct was seen in 2 patients, and the other 3 patients showed segmental narrowing of the body and tail of the dorsal pancreatic duct. Marked stricture of the bile duct was detected in 23 patients and their initial symptom was obstructive jaundice. Six patients showed moderate stenosis to 30%-40% of the normal diameter, and the other 3 patients showed no stenosis of the bile duct. Although marked stricture of the bile duct was detected in 23 of the 27 patients (85%) who showed narrowing of both the ventral and dorsal pancreatic ducts, it was not observed in the 5 patients who showed only involvement of the dorsal pancreatic duct (P = 0.0006). Conclusion: Both the ventral and dorsal pancreatic ducts were involved in many patients with AIP, while in 5 patients only the dorsal pancreatic duct was involved. The pancreas develops by fusion of the dorsal and ventral pancreatic primordial buds. Although the pathogenesis of AIP is unclear, AIP might have occurred only in the dorsal pancreas in these 5 patients. We would propose a new term of autoimmune dorsal pancreatitis. Although obstructive jaundice due to stenosis of the bile duct commonly occurs with AIP, in this type of the disease, anatomic relationships between the dorsal pancreas and common bile duct suggest that obstructive jaundice rarely occurs, even if the pancreatic head is involved.