An outpouching or in effect a hernia of the swallowing passage just above a non-relaxing cricopharyngeus muscle or upper esophageal sphincter (UES). In essence, the forces of swallowing are delivered against a somewhat unyielding muscle, and this causes the wall of the swallowing passage just above the UES to balloon outward. Though unknown to many, the ZD is only the reflection of the main problem, which is cricopharyngeus dysfunction. Myotomy of the cricopharyngeus muscle tends to resolve symptoms, even though the ZD is left in place and not removed.
Posted in Glossary.