Pancreatic pseudocysts (PP) present as a complication that occurs in 5-15% of acute pancreatitis and 26-40% of chronic pancreatitis (1-3). To date the endoscopic drainage with endoscopic ultrasound (EUS) has replace the surgical treatment due to the similar success and complication rate but with a lower cost and short hospital stay (4-6). Regarding recurrence, it is important to know the anatomy of the main pancreatic duct (MPD). For this purpose, the endoscopic retrograde pancreatography (ERP) has been describe as a useful tool. In fact, many authors perform it before the endoscopic drainage while others wait several weeks after the drainage (7-9) with similar technical success (5,8). However, there are no studies that compare the technical difficulty and the total cost between these two approaches.

METHODS: Random control trial between two groups. Group 1 the ERP will be performed the same day of the endoscopic drainage of PP. Group 2 the ERP will be performed 6 weeks after the endoscopic drainage of PP. Each ERP will be performed by an expert in ERP in patients who fulfilled the Atlanta criteria for PP. The patients will be enrolled and informed consent will be explained and signed. In those patients who ERP fails, a second attempt will be performed 6 weeks after the endoscopic drainage of PP (Group 1) or a magnetic resonance cholangiopancreatography will be performed (Group 2).

Inclusion Criteria:

1. Pancreatic pseudocyst that fulfilled the Atlanta Classification
2. Symptomatic pancreatic pseudocyst
3. Informed consent obtained

Exclusion Criteria:

1. Patient unwilling to participate
2. Absence of duration time of the pancreatography procedure in the record
3. Absence of the number of weeks between the drainage and the pancreatography