All patients who underwent a EUS guided drainage of post-operative collection between 2002 and 2011 in the endoscopy unit of Erasme hospital will be included for analysis. The study will focus on retrospective analysis of prospectively collected data. The technique is the same as the one used for pancreatic pseudocysts drainage. The technical success is defined as the ability to access and drain the collection by placement of transmural drain and/or stents. Treatment success (regression of collection) is defined as the resolution of the collection as shown on abdominal imaging (CT or MRI) in association with clinical resolution of symptoms at 8 weeks of follow-up.