The primary feature of lateral medullary syndrome (Wallenberg syndrome) is:

• A. Oral Stasis
• B. Incomplete Opening of the Upper Esophageal Sphincter
• C. Nasal Regurgitation
• D. Silent Aspiration

Answer: (B)

Swallowing problems from a brainstem stroke often show up in the pharyngeal phase and the mechanism that opens the upper esophageal sphincter. In lateral medullary (Wallenberg) syndrome, damage to nuclei that control pharyngeal and laryngeal muscles, especially the nucleus ambiguus, disrupts the coordinated swallow and the relaxation of the cricopharyngeus. That makes it hard for the upper esophageal sphincter to open when the swallow should pass into the esophagus, so incomplete opening of the UES becomes the most characteristic feature.

Oral stasis points to problems in the oral phase, which is less typical for this brainstem pattern. Nasal regurgitation and silent aspiration can occur with dysphagia but are not as defining for this syndrome as the specific UES opening deficit produced by impaired pharyngeal and UES coordination.