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==Introduction==
*The [[Oesophagus - Anatomy & Physiology|oesophagus]] is the part of alimentary tract that tends to go wrong least often.
==Functional Anatomy==
*The [[Oesophagus - Anatomy & Physiology|oesophagus]] is a fibromuscular tube, lined by stratified squamous epithelium and lubricated by mucus, salivary, nasal and bronchial secretions, which acts to transport ingesta from the [[Pharynx - Anatomy & Physiology|pharynx]] to the [[Forestomach - Anatomy & Physiology|stomach]].
*Failure of [[Oesophagus - Anatomy & Physiology|oesophageal]] function results in obstruction and in failure of ingesta to pass to the [[Forestomach - Anatomy & Physiology|stomach]].
*In the bovine there may also be failure of [[Eructation - Anatomy & Physiology|eructation]] and [[tympany]] may develop.
==Defence Mechanisms==
*The [[Oesophagus - Anatomy & Physiology|oesophagus]] has '''no serosa''' and is covered by the fibrous tissue of the neck and mediastinum, from which it derives its blood supply.
*Consequently, infection spreads easily and healing is more difficult.
*[[Oesophagus - Anatomy & Physiology|Oesophageal]] disease is therefore difficult to treat and is consequently very serious.
==Developmental Pathology==
===Congenital Achalasia - Megaoesophagus===
[[Image:Megaoes.gif|left|thumb|125px|<small><center>Megaoesophagus (Courtesy of Alun Williams (RVC))</center></small>]]
*This condition has been termed achalasia but this implies (in man) a cardiac sphincter defect, which is not found in the dog.
*A functional rather than a [[#Traumatic Pathology|physical blockage]]
*Inherited disorder in several breeds:
**Autosomal recessive in Fox Terrier.
**Also in Miniature Schnauzer, Great Dane, German Shepherds and others.
**Also in Siamese cats.
====Clinical====
*See at approx. 6-7 months of age when growing quickly.
*Eats food, [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|vomits]], eats again and [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|vomits]] again because [[Oesophagus - Anatomy & Physiology|oesophagus]] has no tone to it.
*[[Oesophagus - Anatomy & Physiology|Oesophagus]] may become extremely dilated producing a megaoesophagus.
*Can affect the whole length of [[Oesophagus - Anatomy & Physiology|oesophagus]].
====Pathogenesis====
*Appears to be due to due to delay in maturation of [[Oesophagus - Anatomy & Physiology|oesophageal]] innervation, either:
**in upper motor neurones of central swallowing centre or
**in the afferent sensory arm of the reflex involved with [http://en.wikipedia.org/wiki/Peristalsis| peristalsis].
*If dog eats from raised bowel may be satisfactory as food goes down by gravity.
*Once in [[Forestomach - Anatomy & Physiology|stomach]] it is passed on normally.
===Megoesophagus Secondary to Dextra-Aorta===
[[Image:Praa.gif|right|thumb|125px|<small><center>Dextra-aorta (Courtesy of Alun Williams (RVC))</center></small>]]
*Vascular rings are congenital abnormalities of the aortic arch system which interfere with [[Oesophagus - Anatomy & Physiology|oesophageal]] function. Normally, the aortic arch, pulmonary artery and ductus arteriosus (ligamentum arteriosum) all lie on the left side of the [[Oesophagus - Anatomy & Physiology|oesophagus]].
*However, when there is anomalous development of the aortic arch, for example in the [[right-sided arch]], the [[Oesophagus - Anatomy & Physiology|oesophagus]] becomes enclosed within a ring formed by the '''heart base''', '''aorta''', '''ductus arteriosus''' and '''pulmonary artery'''.
*The compression and stricture produced by the “ring” presents passage of solid food beyond the heart base and food accumulates rostral (cranial) to the obstruction, resulting in dilatation or megaoesophagus.
*In most cases food is eventually regurgitated undigested.
*The condition is seen in pups just after weaning and if these are presented for treatment before severe dilatation occurs, then surgical correction of the ring (if possible) offers a good prognosis.
==Erosive & Ulcerative Pathology==
==Vesicular Pathology==
==Neutrophilic Inflammation==
==Granulomatous and pyogranulomatous Inflammation==
==Eosinophilic Inflammation==
==Necrotizing Inflammation==
==Lymphocytic and plasmacytic Inflammation==
==Immune Mediated Pathology==
===Autoimmune===
====Myasthenia Gravis====
*Animals develop antibodies to nicotinic acetylcholine receptors.
*Results in generalised muscle weakness and or megaoesophagus.
====Key-Gaskell syndrome====
*Autonomic polyganglioneuropathy in cats
*Abnormal function of the sympathetic and parasympathetic system.
*Whole autonomic system involved – affected animals usually die.
**Similar to [[Intestines - physical disturbances#Equine dysautonomia, or grass sickness|grass sickness]] in horses.
=====Clinical=====
*Cats show:
**Mega-oesophagus
**Dilated pupils
**Whole gut is involved (very little peristalsis)
**Constipation.
*Generalised autonomic effects:
**Reduced salivation
**Reduced lachrymation
**Bradycardia
**Constipation
**Pupillary dilatation
=====Pathology=====
*Histologically there is marked reduction in the number of neurones in all autonomic ganglia in the ventral horn of all levels of spinal cord accompanied by proliferation of non-neuronal cells.
*Similar changes in brain stem nuclei of cranial nerves.
=====Pathogenesis=====
*Acquired disease - outbreaks occurred in the past, now only occasionally seen but seems to be getting more common again.
*Possibly toxic cause.
*Possibly in dry food or in vaccine?
*Agent not really known, but produces general damage to autonomic nervous system.
===Hypersensitivity===
==Proliferative Pathology==
===Hyperplastic===
===Papular===
====Bovine Papular Stomatitis====
[[Image:BPSOES.gif|right|thumb|125px|<small><center>Oesophageal lesions of BPS (Courtesy of Alun Williams (RVC))</center></small>]]
Lesions of [[Cavity & Gingiva - Pathology#Bovine Papular stomatitis|Bovine Papular Stomatitis]] may also be found in the [[Oesophagus - Anatomy & Physiology|oesophagus]].
===Neoplastic===
====Upper Alimentary Tract Carcinoma Complex====
=====Aetiology=====
*The most important [[Oesophagus - Anatomy & Physiology|oesophageal]] neoplasm is squamous cell carcinoma in the cow.
*This tumour is seen as part of a more general syndrome of upper alimentary tract neoplasia in adult cattle grazing rough pasture on which the '''bracken fern''' (Pteridium aquilinum) is present.
*The syndrome is seen in various part of the world including the Western Highlands of Scotland, Brazil and Kenya.
*In affected animals, squamous carcinomas may be present in the [[Oral Cavity - Oropharynx - Anatomy & Physiology|oropharynx]], [[Oesophagus - Anatomy & Physiology|oesophagus]] and [[The Rumen|rumen]] and there may also be [[intestinal adenocarcinomas]] and bladder tumours, or the condition known as [[enzootic bovine haematuria]].
=====Pathogenesis=====
*Experimentally, the feeding of bracken to laboratory animals will result in alimentary and [[Bladder - Anatomy & Physiology|bladder]] tumours.
*However, in many naturally-occurring cases of upper alimentary carcinoma in cattle there are coexisting viral papillomata, some of which show malignant change.
*The relationship between the ingestion of bracken and the presence of virus in the aetiology of the malignancies is currently the subject of intensive investigations.
*It may be that both are involved in the carcinogenesis.
=====Macroscopically=====
*These upper alimentary squamous carcinomas are most often seen as:
**large
**fungating
**often superficially-necrotic
**protruding into the lumen of the [[Alimentary - Anatomy & Physiology|alimentary tract]];
*There is often a marked scirrhous reaction.
*The tumours are locally aggressive and may permeate local lymphatics and metastasise to local lymph nodes.
=====Microscopically=====
The tumour consists of cords or groups of squamous cells, which may form keratin.
Individual or multiple papillomata may be found in association with the carcinomata.
*The presence of the tumours interferes with normal alimentary function
**there may be difficulty in chewing and [[Deglutition|swallowing]] or in cudding and [[Eructation - Anatomy & Physiology|eructation]].
====Squamous Cell Carcinoma of Other Species====
*Squamous cell carcinomas of the [[Oesophagus - Anatomy & Physiology|oesophagus]] are occasionally seen in other species, notably in the cat, where the tumour tends to infiltrate around the oesophageal wall resulting in a “'''ring carcinoma'''”.
*The affected cat has progressive difficulty in eating and [[Deglutition|swallowing]].
==Degenerative Pathology==
===Acquired megaoesophagus===
*Occurs spontaneously in adult in any disorder that disrupts normal reflex involved in swallowing either peripheral or central.
*These can include:
**Viral encephalitides
**Peripheral neuropathies
***Degeneration or inactivity of local myenteric nerve plexuses (Auerbach’s plexuses),
***or to lesions in the vagus nerve or the central nucleus in the medulla of the brain which supply the [[Oesophagus - Anatomy & Physiology|oesophagus]].
**Poisonings such as:
***Lead
***Tetanus
***Botulism
**Myopathies.
*The result is the presence of a hypotonic [[Oesophagus - Anatomy & Physiology|oesophagus]] in which food accumulates causing distension
*Usually the thoracic oesophagus from the thoracic inlet to the diaphragm is affected and grossly the [[Oesophagus - Anatomy & Physiology|oesophagus]] is dilated, thin-walled and hypotonic.
==Metabolic Pathology==
==Nutritional Pathology==
==Traumatic Pathology==
===Impaction===
{| style="color:darkblue;background-color:#ffffcc;" cellpadding="10" cellspacing="0" border="1"
|'''Upper Block'''
|'''Lower Block'''
|-
| Acute vomiting
| Gradual intestinal distention
|-
| Dehydration
| Mucosal destruction
|-
| Alkalosis
| Toxaemia
|-
| Pre-renal azotaemia
| Peritonitis
|}
*Commonly in cattle, horses and dogs.
*The most common sites of obstruction are the '''thoracic inlet''', '''the base of the heart''', and the '''hiatus oesophagus''' of the diaphragm, i.e.: the narrowest points.
====Clinical Signs====
====Horse====
*With foods that expand in [[Oesophagus - Anatomy & Physiology|oesophagus]] such as haylage etc.
*Also seen with whole apples.
====Cattle====
[[Image:Bovimpaction.gif|right|thumb|125px|<small><center>Impaction of a bovine oesophagus (Courtesy of Alun Williams (RVC))</center></small>]]
*May eat a spherical object that obstructs the [[Oesophagus - Anatomy & Physiology|oesophagus]] mostly in anterior 1/3rd of [[Oesophagus - Anatomy & Physiology|oesophagus]] and can often be palpated in live animal.
*Potatoes can be a cheap source of feed and if fed whole can become stuck in [[Oesophagus - Anatomy & Physiology|oesophagus]].
*If obstruction occurs further down can be difficult to diagnose and remove.
*Cattle develop bloat when [[Oesophagus - Anatomy & Physiology|oesophagus]] obstructed.
*Apples fairly easily to dislodge.
====Dog====
*Usually with small bones
*Animals that feel protective of feed may gulp food down quickly, particularly if given small chops / knuckle bones.
*Knobbly shape may make bone lodge in [[Oesophagus - Anatomy & Physiology|oesophagus]], particularly just anterior to heart.
*Very difficult to dislodge (because of shape).
*Pressure necrosis occurs very quickly around it and can erode through [[Oesophagus - Anatomy & Physiology|oesophagus]] within about 24 hours.
*Small bone may also lodge in [[Duodenum - Anatomy & Physiology|duodenum]] if they pass through the [[Forestomach - Anatomy & Physiology|stomach]].
===Rupture===
*Perforation may occur with sharp foreign bodies. This may lead to [[cellulitis]] or [[pleurisy]] and other complications.
*Rupture of the [[Oesophagus - Anatomy & Physiology|oesophagus]] admits pathogenic organisms to the mediastinum and fascial planes of the neck. Both are composed of loose connective tissue and communicate with each other.
*Infection spreads rapidly as a cellulitis, aided possibly by peristalsis and pulsation of the carotid arteries, and soon leads to pleurisy.
*'''Rupture is almost always fatal.'''
==Vascular Pathology==
==(Other)==
==Learning Tools==
[[Alimentary Flashcards - Pathology#Oesophagus Flashcards|Oesophagus Flashcards]]