Definition

Regurgitation is the most important clinical sign of esophageal disease and should be differentiated from dysphagia and gagging of more proximal gastrointestinal disorders, and from vomiting of more distal gastrointestinal disorders. Regurgitation differs from vomiting in that it is characterized by the passive retrograde evacuation of undigested food from the esophagus. Vomiting is characterized by coordinated activities of the gastrointestinal, musculoskeletal, and nervous systems culminating in active evacuation of digested or partially digested food from the gastrointestinal tract.¹ Vomiting usually signifies disease caudal to the gastroesophageal sphincter. Severity of clinical signs with esophageal disease is dependent upon the pathogenesis of the disease. For example, animals with vascular ring anomaly may have severe regurgitation, but the appetite is usually excellent because of secondary malnutrition. On the other hand, animals with inflammatory esophageal disease may have anorexia, dysphagia, odynophagia (pain on swallowing), and salivation without much evidence of regurgitation. The latter group clearly presents a diagnostic challenge because of the differing clinical signs. For example, signs referable to aspiration pneumonia, coughing and dyspnea, may be the major presenting complaint in some animals. A good history usually elicits the other signs of esophageal disease in those patients.

Pathophysiology and Mechanisms

Transport of ingested liquids and solids from oral cavity to stomach is the major function of the esophagus. Anatomic structures that permit this function are striated muscle of the cranial esophageal sphincter (cricopharyngeus), striated and smooth muscle of the esophageal body, and smooth muscle of the caudal esophageal (gastroesophageal) sphincter. An important species difference between dogs and cats is in the musculature of the esophageal body. The full length of the canine esophageal body is composed of striated muscle, whereas the distal one-third to one-half of the feline esophageal body is composed of smooth muscle. Striated muscle of the cranial esophageal sphincter and esophageal body is innervated by somatic branches (glossopharyngeal, pharyngeal, and recurrent laryngeal) of the vagus nerve arising from the brainstem nucleus ambiguus. Smooth muscle of the esophageal body and caudal esophageal sphincter is innervated by autonomic branches (esophageal) of the vagus nerve arising from the dorsal motor nucleus of the vagus (see Figure 13-1).²

Anatomic and physiologic differences in canine and feline esophagus have been highlighted in several previous studies.^3–6 During fasting elevated pressures of the cranial and caudal esophageal sphincters prevent movement of food and chyme into the esophageal body from the oral cavity and stomach, respectively. When an animal swallows the cranial esophageal sphincter relaxes to permit movement of liquids and solids into the proximal esophageal body. Swallowing also initiates a wave of peristaltic contractions (primary peristalsis) in the esophagus that transports food into the distal esophageal body. Primary peristaltic contractions are reinforced by a secondary wave of contraction (secondary peristalsis) physiologically mediated by intraluminal distention. The caudal esophageal sphincter relaxes in advance of the propagated pressure wave to permit food to empty into the stomach. Once the bolus of food has passed into the stomach, the caudal esophageal sphincter resumes its high resting pressure.

Inflammation (esophagitis, gastroesophageal reflux, esophageal fistulae), hypomotility (idiopathic megaesophagus, dysautonomia, diverticula), and obstruction (stricture, hiatal hernia, neoplasia, intussusception, foreign bodies, vascular ring anomalies) are the major pathophysiologic processes involving the esophagus of dogs and cats.⁷ With mild esophagitis and hypomotility lesions, the esophagus may undergo healing without further complication. In more severe cases the esophagus may respond with extensive fibrosis, muscular hypertrophy, esophageal narrowing, and/or loss of neural regulation (i.e., flaccidity). Luminal flow is directly related to the fourth power of esophageal radius so that even small diminutions result in significant reductions in esophageal transit.

Differential Diagnosis