Dynamic disorders of swallowing are caused by lesions of the neuro-muscular system that participates in swallowing. Aspiration resulting from such disorders can be classified into four types. This classification is helpful for selecting surgical treatments for aspiration as well as for difficulty in swallowing.
Type I. In this type, aspiration occurs when the larynx is elevated and closed during swallowing. It results from incomplete laryngeal closure. Mediofixation of the paretic vocal fold, suture of the bilateral ventricular folds, and/or fixation of the larynx in a high position yields good laryngeal closure. Cricopharyngeal myotomy leads bolus easily into the esophagus.
Type II. Aspiration takes place when the larynx descends and opens at the end of the second stage of swallowing. This type of aspiration results from a weak propelling force and/or a strong resistance at the entrance of the esophagus. The weak propelling force is attributed to an incompetent velopharyngeal closure, disturbances of tongue movement and/or a weak pharyngeal peristalsis. Pharyngeal flap operation, infrahyoid myotomy and/or reinforcement of the pharyngeal wall is the choice of treatment. In order to reduce the resistance at the entrance of the esophagus, cricopharyngeal myotomy and a fixation of the larynx in an antero-superior position are effective.
Type III. Aspiration occurs in both phases of laryngeal rising and falling.
Type IV. This type is observed in those patients who are unable to execute the movements of the second stage of swallowing. The inability of the second stage movements seems to be caused by one of the following two: a severe paralysis of the swallowing muscles and strong inhibitory stimuli to the swallowing center of the medulla oblongata. The latter is observed in those patients who would have a very severe aspiration if their swallowing center allowed them to execute swallowing. In this type, the bolus is transported from the mouth to the pharynx by the gravity and weak tongue movements. The larynx closes in reflex but does not present such rising and falling as are executed in normal second stage. When the larynx opens, the bolus staying in the pharynx enters the airway.
