Zenker’s diverticulum, often referred to as a pharyngeal pouch, is an outpouching or sac that develops in the pharynx, the part of the throat connecting the mouth and nose to the esophagus. This condition is classified as a pulsion diverticulum, caused by internal pressure pushing the tissue outward. The pouch forms due to a failure in the swallowing mechanism, which allows the inner lining of the throat to herniate through a specific weak point in the muscular wall.
The Specific Anatomical Location
The diverticulum forms in a specific, naturally weak area of the muscular wall of the lower throat, known as the hypopharynx, just above the entrance to the esophagus. This site is formally called Killian’s triangle or Killian’s dehiscence, representing a small gap in the continuous ring of muscle. The area is bordered superiorly by the oblique fibers of the thyropharyngeus muscle (the upper part of the inferior pharyngeal constrictor muscle). Inferiorly, the gap is bordered by the horizontal fibers of the cricopharyngeus muscle, which functions as the upper esophageal sphincter. Since the pouch forms by the inner layer pushing through the outer muscular wall and does not contain all layers of the esophageal wall, it is technically classified as a “false” diverticulum.
Failure of the Cricopharyngeal Muscle
The immediate cause of Zenker’s diverticulum formation is a dysfunction of the cricopharyngeal muscle. This muscle forms the upper esophageal sphincter and is normally tightly closed. When swallowing, the muscle briefly relaxes and opens, allowing the food bolus to pass into the esophagus. In affected individuals, the cricopharyngeal muscle fails to relax completely or coordinate its opening with the contraction of the pharyngeal muscles. This discoordination effectively creates an obstruction at the entrance to the esophagus. The inability of the muscle to open correctly means the descending food bolus meets resistance.
The Role of Intraluminal Pressure
The failed relaxation of the cricopharyngeal muscle directly leads to an increase in pressure within the hypopharynx, the area just above the obstruction. When the powerful pharyngeal muscles contract to push food down, and the upper esophageal sphincter remains closed or fails to open adequately, the force of the swallow is contained in a confined space. This trapped force generates abnormally high intraluminal pressure. The increased pressure then seeks the path of least resistance, which is Killian’s triangle. Over time, this repetitive, excessive pressure pushes the inner mucosal layer of the throat outward through the muscular gap, forming the characteristic sac.
Primary Risk Factors for Development
The mechanical failure of the cricopharyngeal muscle is typically associated with advanced age. The condition overwhelmingly affects older adults, and this prevalence may be linked to age-related changes, such as decreased elasticity and coordination in the swallowing muscles. Zenker’s diverticulum is also more commonly observed in men than in women. Other conditions that place chronic strain on the swallowing mechanism or affect esophageal motility are also associated with the development of the pouch. For example, chronic gastroesophageal reflux disease (GERD) has been suggested as a factor that may contribute to the muscle dysfunction that precedes the formation of the diverticulum.