Anatomy of inferior end of palatopharyngeus: its contribution to upper esophageal sphincter opening

PURPOSE: The palatopharyngeus is one of the longitudinal pharyngeal muscles which contributes to swallowing. It is reported that the palatopharyngeus has muscle bundles in various directions and with attachment sites, and each muscle bundle has a specific function. Although previous reports suggest that the palatopharyngeus is partly interlaced with some parts of the inferior constrictor, the precise relationship remains unclear. The purpose of this study was to examine the precise manner of the connection between the palatopharyngeus and inferior constrictor, and to examine the histological characteristics of this connection. METHODS: We examined 15 halves of nine heads from Japanese cadavers (average age: 76.1 years); 12 halves, macroscopically, and three halves, histologically. RESULTS: Our observation suggests that the palatopharyngeus spreads radially on the inner aspect of the pharyngeal wall. The most inferior portion of the palatopharyngeus extended to the inner surface of the cricopharyngeal part of the inferior constrictor. Histological analysis showed that the inferior end of the palatopharyngeus continued into the dense connective tissue located at the level of the cricoid cartilage. The dense connective tissue not only covered the inner surface of the inferior constrictor but also entered its muscle bundles and enveloped them. CONCLUSION: Therefore, the palatopharyngeus interlaced the cricopharyngeal part of the inferior constrictor through the dense connective tissues. The findings of this study show that the palatopharyngeus may act on the upper esophageal sphincter directly and help in its opening with the aid of the pulling forces in the superolateral direction.