CHAPTER 78 Esophageal Obstruction
Esophageal obstruction, or “choke,” is not an uncommon emergency condition of the horse and is the most common disorder of the esophagus. It is treated as an emergency condition because the horse is unable to eat or drink, can become dehydrated and metabolically acidotic, and can develop aspiration pneumonia if the condition is left untreated. It can occur in horses of any age, breed, or sex, although some predispositions exist. The esophageal obstruction is usually caused by typical feeds such as hay or grain, but it can be caused by ingestion of carrots, apples, corncobs, shavings, hair, or other foreign materials. Clinical signs are diagnostic but should be differentiated from other potential causes; horses with recurrent choke and other systemic signs of illness should be carefully examined for predisposing causes.
In the horse, the esophagus courses from the pharynx down the left side of the neck (cervical portion), into the mediastinum (the thoracic portion), and eventually through the diaphragm (abdominal portion) and into the stomach. The esophagus transports food, water, and saliva from the pharynx into the stomach. The cardiac sphincter lies at the entry to the stomach to prevent gastroesophageal reflux. The esophagus has several layers. The inner layer is epithelium, followed by submucosa, muscle, and then adventitial tissue. The abdominal portion has a serosal outer layer. The muscle layer is composed of both striated and smooth muscles in the proximal two thirds and primarily smooth muscle in the distal portion of the esophagus. This difference in muscle composition in different parts of the esophagus is important in the function of the esophagus and in drug selection for the treatment of choke. The nerve supply to the esophagus is provided by the vagus nerve. The esophageal and pharyngeal branches of this nerve supply the striated muscle and parasympathetic nerves supply the smooth muscle. Throughout the length of the esophagus, the blood supply comes from multiple small arteries of various origins.
Choke can be caused by a primary intraluminal obstruction such as feed, or it can arise secondary to an extraluminal compressive mass or functional problem. Older ponies or horses with poor dentition, young horses with erupting teeth, or horses that eat quickly are thought to be prone to choking because they masticate feed poorly. Among neoplastic conditions, squamous cell carcinoma is the most common esophageal neoplasm, but large thyroid tumors, parotid gland melanoma, and other external swelling or trauma will predispose to choking because they cause extraluminal obstruction. Congenital abnormalities such as duplication cysts, megaesophagus, and neuromuscular disorders also predispose horses to choke. Prior episodes of choke or trauma may cause formation of a diverticulum or strictures of the esophagus, which would lead to a predilection for repeat obstructions. Iatrogenic causes of choke also exist, especially eating too soon after sedation or general anesthesia when coordinated neuromuscular swallowing has not yet returned. In one study of 61 cases of esophageal obstruction, feed was the culprit in 27, strictures in 18, diverticula in 5, and perforation in 11. In another study of 34 cases of choke, 28 cases were secondary to feed impactions.
In general, the clinical signs of esophageal obstruction are indicative of the condition and include dysphagia, ptyalism, coughing, flexion and extension of the neck, and feed and saliva in the nostrils. Horses are often sweating and appear to be distressed by the obstruction and can become dehydrated quickly because of loss of fluids through saliva and sweat. There may be a palpable swelling in the cervical area of the neck. signs of emphysema, heat, or cellulitis should lead to a suspicion of esophageal perforation. Differential diagnoses include an oral obstruction such as a lingual abscess, pharyngeal trauma, botulism and other neuromuscular diseases, grass sickness, rabies, or spontaneous reflux concomitant with severe colic. A horse with recurrent episodes of choke should prompt careful observation of body condition and examination for dental abnormalities or other underlying issues.
Diagnosis of esophageal obstruction in horses is most commonly based on a combination of the clinical signs and the inability to easily pass a nasogastric tube. Other diagnostic modalities can be used, particularly in cases of recurrent obstruction or ones that fail to resolve readily with treatment.