To study the influence of different types of periampullary diverticulum(PAD) on ERCP difficult cannulation and postoperative complications.

Periampullary diverticula (PAD) are extraluminal out-pouching of the duodenum mucosa often occurring within a radius of 2-3 cm from the ampulla of Vater or hepatopancreatic ampulla. More PAD cases have been identified over recent years, and it's generally believed that up to 27% of elderly cases may have PAD. Several classifications of PAD have been proposed, and the most commonly used distinguishes intraluminal and extraluminal diverticula. Recent studies suggest that PAD is a risk factor for the development of bile duct diseases, and it may cause endoscopic retrograde cholangiopancreatography (ERCP) procedures to fail, but some other studies have come to the opposite conclusion.

During ERCP procedures, the investigators found that different types of PAD seem to have some differences in the size of the diverticulum, difficulty in intubation, and complications. The investigators plan to this retrospectively study collecting 4 years of cases to evaluate the clinical features of different types of PAD in terms of difficult cannulation and complications.

Inclusion Criteria:

• 18-90 years old ERCP patients
• With native papilla

Exclusion Criteria:

• Unwillingness or inability to consent for the study
• Coagulation dysfunction (INR> 1.5) and low peripheral blood platelet count (<50×10^9 / L) or using anti-coagulation drugs
• Previous ERCP
• Prior surgery of Bismuth Ⅱ, Roux-en-Y and Cholangiojejunostomy
• Preoperative coexistent diseases: acute pancreatitis, GI tract hemorrhage or perforation, severe liver disease(such as decompensated liver cirrhosis, liver failure and so on), septic shock
• Biliary-duodenal fistula confirmed during ERCP
• Pregnant women or breastfeeding

18-90 years old patients with ERCP indications