Joe Mayhew - Large Animal Neurology

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3 3 Giguère S, Weber EJ and Sanchez LC. Factors associated with outcome and gradual improvement in survival over time in 1065 equine neonates admitted to an intensive care unit. Equine Vet J 2017; 49(1): 45–50.

4 4 Vidovic A and Delling U. Aryepiglottic fold augmentation as treatment for late‐onset dysphagia following surgical treatment of recurrent laryngeal neuropathy. Tierarztl Prax Ausg G Grosstiere Nutztiere 2017; 45(4): 219–225.

5 5 Barakzai SZ, Dixon PM, Hawkes CS, Cox A and Barnett TP. Upper esophageal incompetence in five horses after prosthetic laryngoplasty. Vet Surg 2015; 44(2): 150–155.

6 6 Dixon RM, McGorum BC, Railton DI, et al. Long‐term survey of laryngoplasty and ventriculocordectomy in an older, mixed‐breed population of 200 horses. Part 1: Maintenance of surgical arytenoid abduction and complications of surgery. Equine Vet J 2003; 35(4): 389–396.

7 7 Gomez DE, Desrochers A, Francoz D, et al. Pharyngeal trauma in dairy cattle: 27 cases. J Vet Intern Med 2019; 33(4): 1833–1839.

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Dilated esophagus can be due to obstruction or primary dysfunction of the esophagus. Permanent dilation of the esophagus or megesophagus is not frequently seen in large animals. However, it has been observed with chronic intra‐ and extraluminal esophageal obstruction caused by lower esophageal sphincter scarring and ulceration, persistent right aortic arch, severe pneumonia with dyspnea and with gastroesophageal ulceration, and associated bruxism, retching and aerophagia. Such causes are far more common than primary neuromuscular esophageal dysfunction that does however occur in the proximal esophagus as a complication of laryngeal surgery. 1

Regional aganglionosis and deficiency of neural elements have been purported to be congenital neural causes of megaesophagus. 2Also, some young foals showing nasal regurgitation of milk may have primary esophageal muscular lesions seen at postmortem examination; however, others diagnosed as having neonatal encephalopathy do well with supportive care so euthanasia should not be embarked upon too quickly. 3–5

Figure 16.1 Dilation of the esophagus with regurgitation in large animals is most frequently due to upper gastrointestinal obstruction or due to functional disorders such as equine dysautonomia and ruminant vagal indigestion. Megaesophagus can accompany botulism, but otherwise it is only rarely seen without an esophageal stricture. These two cases demonstrated with contrast esophagram (A and B) had acquired, mild, generalized, fluctuant, somatic weakness and poor esophageal function of several months duration for which there was no definitive pathologic lesion determined.

A dilated esophagus is seen in several diffuse myasthenic syndromes, many of which defy specific diagnosis ( Figure 16.1), and some degree of paresis and dilation of the esophagus is one of the hallmarks of the paralytic gastrointestinal syndrome in horses from Europe and from Patagonia, known as grass sickness and Mal Seco, respectively.

A familial form of megaesophagus particularly involving the thoracic esophagus occurs in Friesian horses in Europe which is associated with increased deposition of disorganized collagen mainly in the nondilated portion of the esophagus and a decrease in neural elements. 6,7