Killian's is it a True Dehiscence? An Anatomical Perspective.

Objective Zenker's diverticulum is a pulsion outpouching from the posterior pharyngeal wall. The anatomy of the wall has been proposed to be dehiscent in the region of the Killian's triangle, between the thyropharyngeus muscle (inferior pharyngeal constrictor) and the cricopharyngeus muscle. A dehiscence is a bursting open, splitting or gaping along natural or sutured lines. To the best of our knowledge, there have not been any studies to histologically analyze the posterior pharyngeal wall and the exact location of the dehiscence. We thus aim to determine the presence and characteristics of this area of possible dehiscence.  Methods Fifty-eight cadavers were analysed. A portion of tissue was excised within the borders of the Killian's triangle, being the inferior border of the oblique inferior constrictor muscle and the superior border of the cricopharyngeus muscle from the posterior wall of the pharynx. Four longitudinal sections were sampled from each cadaver including: left lateral, left medial, right medial and finally the right lateral aspect of the posterior pharyngeal wall. These samples were then embedded in wax and cut with a microtome at 5 microns. They were then placed on microscope slides and stained with Haematoxylin and Eosin and analysed in terms of thickness and histology. Results There was significant overlapping of the thyropharyngeus and cricopharyngeus muscles seen macroscopically in all cadavers that were dissected. No obvious area of dehiscence was found in any of the specimens, however, there were variations in the thickness of the posterior pharyngeal wall within the thyropharyngeus muscle. When comparing the left- and the right-hand sides of the thyropharyngeus, the mean measurement of the left medial muscle sample was found to be significantly thinner than the mean measurement of the right medial muscle sample (95% CI Inf to -44.39, p-value = 0.0189). The average of both the thickest and thinnest muscle measurements for each of the four samples was then compared. The average left medial muscle layer was found to be significantly thinner than the average right medial muscle layer (95% CI Inf to -9.81, p-value = 0.03822). Conclusion This study demonstrated that the left thyropharyngeal muscle was thinner than the right. However, no dehiscent areas were found in any of the specimens. Significant overlapping of the cricopharyngeus and thyropharyngeus muscles was noted. Thus, we propose that the hypopharyngeal pouch, given enough intraluminal pharyngeal pressure, may occur between the fibres of the inferior pharyngeal constrictor muscle rather than between the cricopharyngeus and the inferior pharyngeal constrictor muscles. As a dehiscence occurs between a natural or sutured line, of which there is neither in the thyropharyngeus muscle, we propose that the term Killian's dehiscence is a misnomer and that the defect instead meets the definition of a hernia.