marsupialize /märso̅o̅″pē·əlīz/ [L, marsupium, pouch; Gk, izein, to cause] , to form a pouch surgically to treat a cyst when simple removal would not be effective, such as in a pancreatic or a pilonidal cyst. The cyst sac is opened and emptied. Its edges are sutured to adjacent tissues, and a drain is left in place. Secretions decrease over a period of several months and may eventually cease.