Changes

====Congenital Idiopathic Megaoesophagus====

====Congenital Idiopathic Megaoesophagus====

[[Image:Megaoes.gif|left|thumb|125px|<small><center>Megaoesophagus (Copyright Alun Williams 2009 (RVC))</center></small>]]

[[Image:Megaoes.gif|left|thumb|125px|<small><center>Megaoesophagus (Copyright Alun Williams 2009 (RVC))</center></small>]]

Congenital megaoesophagus is sometimes called 'congenital achalasia' but this implies a defect of the cardiac sphincter of the stomach (as in man) whereas the canine condition affects the whole oesophagus.  This disease is inherited in a number of breeds of dog, including the fox terrier (in an autosomal recessive manner), miniature Schnauzer (dominantly with 60% penetrance), great Dane, Irish setter, Chinese Shar-pei, Newfoundland and German shepherd.  It is also an inherited disorder of the Siamese cat where it may occur with concurrent pyloric stenosis.

Congenital megaoesophagus is sometimes called 'congenital achalasia' but this term implies a defect of the cardiac sphincter of the stomach (as in man) whereas the canine condition affects the whole oesophagus.  This disease is inherited in a number of breeds of dog, including the fox terrier (in an autosomal recessive manner), miniature Schnauzer (dominantly with 60% penetrance), great Dane, Irish setter, Chinese Shar-pei, Newfoundland and German shepherd.  It is also an inherited disorder of the Siamese cat where it may occur with concurrent pyloric stenosis.

The disease is thought to result from a delay in the maturation of either upper motor neurones in the central swallowing centre in the brainstem or of the afferent sensory arm of the peristaltic reflex.  The resultant hypomotility of the oesophagus leads to a functional obstruction and boluses of food do not reach the stomach and are eventually regurgitated.  The condition is seen most commonly at 6-7 months during a period of rapid growth.  Affected animals eat, regurgitate shortly afterwards and may then attempt to eat again.  As with any disease that results in chronic regurgitation, affected animals lose weight due to '''malnutrition''' and may also develop '''aspiration pneumonia'''.

The disease is thought to result from a delay in the maturation of either upper motor neurones in the central swallowing centre in the brainstem or of the afferent sensory arm of the peristaltic reflex.  The resultant hypomotility of the oesophagus leads to a functional obstruction and boluses of food do not reach the stomach and are eventually regurgitated.  The condition is seen most commonly at 6-7 months during a period of rapid growth.  Affected animals eat, regurgitate shortly afterwards and may then attempt to eat again.  As with any disease that results in chronic regurgitation, affected animals lose weight due to '''malnutrition''' and may also develop '''aspiration pneumonia'''.

====[[Vascular Ring Anomalies|Vascular Ring Anomalies]]====

====[[Vascular Ring Anomalies|Vascular Ring Anomalies]]====

[[Image:Praa.gif|right|thumb|125px|<small><center>Dextra-aorta (Courtesy of Alun Williams (RVC))</center></small>]]

[[Image:Praa.gif|right|thumb|125px|<center>Post-mortem specimen of an animal with a persistent right aortic arch <br><small> Copyright Alun Williams 2009 (RVC))</center></small>]]

Vascular rings are congenital abnormalities of the aortic arch system which interfere with [[Oesophagus - Anatomy & Physiology|oesophageal]] function. Many vascular anomalies (such as an aberrant right subclavian artery) are clinically silent and up to 20% of dogs and cats possess such an anomaly.  Clinically significant anomalies are found most commonly in large breed dogs, particularly Irish setters and German Shepherd dogs.   

Vascular rings are congenital abnormalities of the aortic arch system which interfere with [[Oesophagus - Anatomy & Physiology|oesophageal]] function. Many vascular anomalies (such as an aberrant right subclavian artery) are clinically silent and up to 20% of dogs and cats may possess such an anomaly.  Clinically significant anomalies are found most commonly in large breed dogs, particularly Irish setters and German Shepherd dogs.   

The most common clinically significant anomaly is a '''dextra-aorta''' or '''persistent right aortic arch''', in which the aorta is formed by the fourth right branchial arch rather than the fourth left arch.  In the normal animal, the aorta, pulmonary artery and ductus arteriosus (which connects the former vessels) all lie on the left side of the oesophagus but, when the aorta develops on the right, the ductus arteriosus must pass across the oesophagus to reach the aorta.  The oesophagus is then trapped within a ring formed by the '''aorta''' (on the right), the '''main pulmonary artery''' (on the left), the '''ductus arteriosus''' (or ligamentum arteriosum) dorsally and the '''heart base''' ventrally.  The compression and stricture produced by the vascular ring prevents the passage of solid food beyond the heart base and food accumulates cranial to the obstruction.  This results in dilation (megaoesophagus) which is usually confined to the cranial thoracic region but, in chronic cases, may extend along its whole length.

The most common clinically significant anomaly is a '''dextra-aorta''' or '''persistent right aortic arch''', in which the aorta is formed by the fourth right branchial arch rather than the fourth left arch.  In the normal animal, the aorta, pulmonary artery and ductus arteriosus (which connects the former vessels) all lie on the left side of the oesophagus but, when the aorta develops on the right, the ductus arteriosus must pass across the oesophagus to reach the aorta.  The oesophagus is then trapped within a ring formed by the '''aorta''' (on the right), the '''main pulmonary artery''' (on the left), the '''ductus arteriosus''' (or ligamentum arteriosum) dorsally and the '''heart base''' ventrally.  The compression and stricture produced by the vascular ring prevents the passage of solid food beyond the heart base and food accumulates cranial to the obstruction.  This results in dilation (megaoesophagus) which is usually confined to the cranial thoracic region but, in chronic cases, may extend along its entire length.

The condition usually becomes apparent at weaning when animals start to eat solid food that cannot pass through the constricted region.  Affected animals tend to regurgitate undigested solid food but, if they are presented for treatment before severe dilation occurs, surgical correction of the ring (if possible) should result in a good prognosis.

The condition usually becomes apparent at weaning when animals start to eat solid food that cannot pass through the constricted region.  Affected animals tend to regurgitate undigested solid food but, if they are presented for treatment before severe dilation occurs, surgical correction of the ring (if possible) should result in a good prognosis.

====[[Myasthenia Gravis]]====

====[[Myasthenia Gravis]]====

Myasthenia gravis is disease of the neuromuscular junction that occurs due to a defect or absence of nicotinic acetylcholine receptors on the post-synaptic membrane (in the congenital form) or due to the presence of antibodies that bind to the receptors and prevent them from functioning normally (in the acquired form).  The classical '''focal''' form of myasthenia gravis affects only the extraocular muscles, the cranial oesophagus and the muscles innervated by cranial nerves V, VII and IX.  80% of animals diagnosed with myasthenia gravis have megaoesophagus at presentation.

Myasthenia gravis is a disease of the neuromuscular junction that occurs due to a defect or absence of nicotinic acetylcholine receptors on the post-synaptic membrane (in the congenital form) or due to the presence of antibodies that bind to the receptors and prevent them from functioning normally (in the acquired form).  The classical '''focal''' form of myasthenia gravis affects only the extraocular muscles, the cranial oesophagus and the muscles innervated by cranial nerves V, VII and IX.  80% of animals diagnosed with myasthenia gravis have megaoesophagus at presentation.

===Acquired Megaoesophagus===

===Acquired Megaoesophagus===

*Any cause of '''prolonged oesophageal obstruction''' may result in megaoesophagus which eventually becomes irreversible if the underlying cause is not removed.  Examples include [[Oesophageal Foreign Body|foreign bodies]], [[Oesophageal Neoplasia|neoplasia]] and [[Oesophageal Stricture|strictures]].

*Any cause of '''prolonged oesophageal obstruction''' may result in megaoesophagus which eventually becomes irreversible if the underlying cause is not removed.  Examples include [[Oesophageal Foreign Body|foreign bodies]], [[Oesophageal Neoplasia|neoplasia]] and [[Oesophageal Stricture|strictures]].

The result is the presence of a hypotonic [[Oesophagus - Anatomy & Physiology|oesophagus]] which is distended by accumulated food material.  The thoracic oesophagus from the thoracic inlet to the diaphragm is usually affected affected animals regurgitate repeatedly, lose weight and may develop aspiration pneumonia.

The result is the presence of a hypotonic [[Oesophagus - Anatomy & Physiology|oesophagus]] which is distended by accumulated food material.  The thoracic oesophagus from the thoracic inlet to the diaphragm is usually dilated and affected animals regurgitate repeatedly, lose weight and may develop aspiration pneumonia.

==Diagnosis==

==Diagnosis==

*With vascular ring anomalies, the oesophagus is usually only dilated cranial to the base of the heart.

*With vascular ring anomalies, the oesophagus is usually only dilated cranial to the base of the heart.

The presence of megaoesophagus can be confirmed by feeding '''barium contrast medium''', either as a liquid or mixed with meat (a 'barium meal').  The advantage of the barium meal is that it distends the oesophagus (to show the extent of its dilation) and it provides better definition of the point of constriction in animals with a vascular ring anomaly.

The presence of megaoesophagus can be confirmed by feeding '''barium contrast medium''', either as a liquid or mixed with meat (a 'barium meal').  The advantage of the barium meal is that it distends the oesophagus to show the extent of its dilation and it provides better definition of the point of constriction in animals with a vascular ring anomaly.

'''Endoscopy''' allows the operator to visualise the dilated oesophagus directly but this is rarely required to reach a diagnosis.

'''Endoscopy''' allows the operator to visualise the dilated oesophagus directly but this is rarely required to reach a diagnosis.

*Use of a '''suitable diet''' fed as small meals several times per day.  A consistency should be used which is tolerated by the individual animal, with some preferring a liquid gruel and others small rolled boluses.

*Use of a '''suitable diet''' fed as small meals several times per day.  A consistency should be used which is tolerated by the individual animal, with some preferring a liquid gruel and others small rolled boluses.

*The '''forelimbs of the animal should be raised''' for 10-15 minutes after each to meal to allow the food to reach the stomach.

*The '''forelimbs of the animal should be raised''' for 10-15 minutes after each to meal to allow the food to reach the stomach.

*The animal should be monitored constantly (by its owner) for the development of signs of '''aspiration pneumonia''', a frequent recurrent problem in animals with congenital megaoesophagus.    This condition should be treated aggressively with intra-venous bactericidal antibiotics (preferably selected on the basis of results from a culture of a broncho-alveolar lavage), coupage and nebulisation.

*The animal should be monitored constantly by its owner for the development of signs of '''aspiration pneumonia''', a frequent recurrent problem in animals with congenital megaoesophagus.    This condition should be treated aggressively with intra-venous bactericidal antibiotics (preferably selected on the basis of results from a culture of a broncho-alveolar lavage), coupage and nebulisation.

[[Category:Oesophagus - Pathology]]

[[Category:Oesophagus - Pathology]]