Morphology of the cricopharyngeal muscle in Zenker and control specimens.

The cricopharyngeal muscle (CPM) is essential for normal deglutition. Pharyngeal dysphagia commonly results from impaired or uncoordinated CPM dilation. Dysfunction of the CPM has also been implicated in the genesis of Zenker's (pharyngoesophageal) diverticulum. Despite the CPM's significance, little is understood about its morphology. We studied CPM biopsy specimens from 20 patients with Zenker's diverticulum and from 5 fresh cadaver patients with detailed histologic techniques to include fiber size and shape and adenosine triphosphatase, reduced nicotinamide adenine dinucleotide, trichrome, succinate dehydrogenase, cytochrome C oxidase, periodic acid-Schiff reaction, oil red O, acid phosphatase, Congo red, crystal violet, and monoadenylate deaminase stains. The normal CPM has unique morphological characteristics, with some myofibers having staining properties that are a hybrid between striated muscle and muscle spindle. The variable orientation of the muscle fibers is also different from that of most other striated musculature. Of the 20 Zenker CPM specimens, 4 specimens did not reveal any significant differences from controls (2 of which had insufficient amounts of tissue for complete analysis). In the remaining 16 specimens, several abnormalities existed, including excessive size variation (16/16), grouping of atrophic fibers (9/16), target or targetoid formations (4/16), cores (2/16), and ragged red fibers (2/16). The final pathological pattern of the 16 specimens was neurogenic in 7, myopathic in 4, and mixed (with neurogenic predominance) in the remaining 5. Two specimens contained significant lymphocytic inflammatory infiltrates. We conclude that the unique neuromuscular function of the CPM in deglutition is likely due to its fiber orientation and the hybrid nature of some of the myofibers. Morphological disturbances of the CPM impair its dilation and may account for the development of Zenker's diverticulum. This disturbance is most often due to progressive denervation of the CPM.