Figure 5 - Normal cricopharyngeus muscle (left) compared to that from a patient with Zenker's (right).

When compared with the normal cricopharyngeus muscle, the muscle from patient with Zenker's demonstrates fiber dropout (due to necrosis, as evidenced by scattered degenerative fibers), greater fiber size variability, and marked increase in fibroadipose tissue replacement. (Source: Cook et al.,³⁷ with permission from Blackwell Publishers.)