An abnormal pouch of tissue that forms at the juncture of the pharynx (lower part of the throat) and the esophagus (the muscular tube that connects the throat to the stomach). Zenker diverticulum is a common type of esophageal diverticulum. The condition is usually diagnosed by an upper gastrointestinal (GI) series (an X-ray procedure that is also called a barium swallow). Zenker diverticulum may not require treatment. However, because food can become trapped in the diverticulum and in¬ haled, a doctor may recommend surgery to correct the problem.