Abstract
A 20-year-old pony mare was presented to the equine hospital with a ten-day history of dysphagia, regurgitation and coughing. An obstruction of the oesophagus was excluded via endoscopy, but the proximal oesophagus appeared to be distended and circular contractions were missing. A guttural pouch endoscopy revealed a single, black-mottled plaque on the pharyngeal ramus of the vagus nerve in the left guttural pouch, causing a local swelling of this nerve. The pharyngeal ramus seemed to be atrophic distal to the lesion. A biopsy was taken from the lesion and histopathological findings proved the reasonable suspicion of a guttural pouch mycosis with a high degree of purulent-necrotic inflammation and invasion of fungal hyphae. There were no signs of neoplasia, such as melanoma. Daily guttural pouch irrigations with a clotrimazole emulsion (20 g Canesten® Gyn4 solved in 500 ml water), led to a good recovery of the mucosa above the nerve. Periodic endoscopic examination of the left guttural pouch showed that local thickening and distal atrophy of this pharyngeal ramus did not improve, neither did the clinical symptoms. Due to progressive weight loss, acute respiratory distress and aspiration pneumonia, the 20-year-old pony mare unfortunately had to be euthanized three weeks after discharge. This case report emphasizes the enormous importance of a single nerve for the realization of the swallowing process. The one-sided loss of function of the pharyngeal branch of the vagal nerve cannot be compensated neither by the remaining ipsilateral nerves nor by the contralateral normal functioning glossopharyngeal and vagal nerves and thus inevitably leads to severe dysphagia.
Highlights
The physiological swallowing process is realized by a complex sequence of over 20 head and neck muscles, involving numerous cranial nerves (V, VII, IX, X, XI, XII)
The pharyngeal branch of the vagus nerve is the most important for the motor innervation of the pharyngeal muscles [2,5]. This sensomotor nerve innervates the palatinus, levator veli palatini, and palatopharyngeus muscles, as well as the dorsal pharyngeal constricting muscles, which include the cricopharyngeus, thryopharyngeus, pterygopharyngeus, and hyopharyngeus muscles. Those constricting muscles are essential for the swallowing process because they are needed to propel feed into the oesophagus [6]
The glossopharyngeal nerve provides sensory innervation to the nasopharynx, to the dorsal and lateral walls of the pharynx, as well as to the nasopharyngeal surface of the proximal half of the soft palate, and supplies motor innervation only to the stylopharyngeus muscle, a muscle which contracts during swallowing and dilates the pharynx [7]
Summary
The physiological swallowing process is realized by a complex sequence of over 20 head and neck muscles, involving numerous cranial nerves (V, VII, IX, X, XI, XII). After feeding, the pony showed severe dysphagia and increased nasal discharge containing lots of masticated food. Endoscopy of the left guttural pouch revealed a small single black-mottled plaque on the pharyngeal branch of the vagus, causing it to swell (Figure 2). This plaque was completely removed via biopsy forceps for pathohistological examination. The nasal passages were full of masticated food, the larynx was symmetrical, and the guttural pouch openings and epiglottis were normal. The pharyngeal branch of the vagus in the left guttural pouch no longer showed any black-mottled plaques, the fungal lesion did not reappear.
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