Page 793 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

768 CHAPTER 4

VetBooks.ir Dissection of the melanoma from the gland tissue is also be associated secondarily with other diseases
virtually impossible, and radiation therapy has been
including rabies, oesophageal obstruction, pharyn-
geal dysphagia and stomatitis. Where the ptyalism is
used to achieve remission in a few cases.
caused by a fungal infection, the excess salivation is
PTYALISM induced by the toxin slaframine, which is a parasym-
pathomimetic. The toxin may also induce lacrima-
Ptyalism or excessive salivation may occur in tion, anorexia and diarrhoea. Investigation should
response to oral pain, periodontal disease, mucosal be directed at identifying the primary cause and
penetration by a foreign body and ingestion of the this should include an oral examination, pharyngeal
fungus Rhizoctonia legumincola. The clinical signs may endoscopy and passage of a nasogastric tube.

DISEASES OF THE OESOPHAGUS

INTRODUCTION long that prevents oesophageal reflux under normal
circumstances.
Anatomy of the equine oesophagus
The equine oesophagus consists of stratified squa- Clinical signs of oesophageal disease
mous mucosa within a spiralling muscular tube, Oesophageal disease often presents as signs of swal-
which contains both striated and smooth muscle lowing difficulties. Dysphagia, hypersalivation,
in the cranial two-thirds and smooth muscle layers and sweating are all associated with oesophageal
only in the caudal third. There is no serosal layer obstruction (Fig. 4.95). Dysphagia can have oral,
and the outer adventitial layer is suspended within pharyngeal and oesophageal causes that can be due
the mediastinium. The oesophagus occupies a posi- to inflammation, neurological dysfunction, pha-
tion dorsal and slightly to the left of the trachea ryngeal or oesophageal trauma or luminal obstruc-
and is closely associated with the carotid arteries tion. Aspiration of food spilling from an obstructed
within the carotid sheath, the cranial sympathetic oesophagus will also result in coughing and can
trunk and the recurrent laryngeal nerves. The lead to aspiration pneumonia. Perforation of the
cranial oesophageal sphincter is about 5 cm long oesophagus can lead to a painful mediastinal cellu-
and comprises the cricopharyngeus and thyropha- litis, while oesophageal reflux syndrome in foals can
ryngeus muscles, which occlude the oesophageal cause intermittent signs of oesophageal pain associ-
lumen when contracted. The cranial dilation of the ated with food ingestion.
oesophageal entrance is in close approximation to
the muscular processes of the larynx that lie ven- Diagnosis of oesophageal diseases
tral to and just caudal to it. During swallowing, the Physical examination
food bolus is voluntarily passed into the pharynx A physical examination should include careful pal-
using the tongue and pharyngeal muscles under a pation of the neck from the larynx to the thoracic
complex mechanism involving cranial nerves IX, inlet for signs of swelling, pain, oedema, cellulites,
X, XI and XII. The larynx is moved ventrally and crepitus or firm masses. General physical param-
caudally, the epiglottis is retroverted as the bolus eters such as circulatory function, hydration status,
passes into the oropharynx and the oesophageal haematological parameters, electrolyte imbalances
sphincter muscles relax, allowing the bolus to pass and neurological examination of the cranial nerves
into the oesophagus. Thereafter, swallowing is an should also be included.
involuntary reflex controlled by branches of the Cautious passage of a round-ended, well- lubricated
vagus (X) nerve. The oesophagus enters the stom- nasogastric (NG) tube should be attempted. It may
ach via the cardiac or caudal oesophageal sphincter, be advisable for the horse to be sedated for this pro-
which is a tight muscular ring approximately 10 cm cedure. The tube is advanced into the nasopharynx