Researchers don’t know the exact cause but think issues with your cricopharyngeus muscle are to blame. This muscle is at the top of your esophagus. It opens (relaxes) to let food in and then closes. When you swallow food, powerful muscles in your throat push food down toward your cricopharyngeus muscle. When this muscle doesn’t relax as it should, food gets caught in a muscular squeeze play that puts pressure on your pharynx wall. Over time, the pressure pushes tissue through the wall to make a pouch.