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Megaoesophagus describes a dilated, hypomotile oesophagus that is not able to effectively transport food from the the pharnyx to the stomach.  The condition may be congenital or acquired and, although it occurs in most of the major domestic species, it is most common in dogs and cats.  The following sections describe the causes of megaoesophagus.

Megaoesophagus describes a dilated, hypomotile oesophagus that is not able to effectively transport food from the the pharnyx to the stomach.  The condition may be congenital or acquired and, although it occurs in most of the major domestic species, it is most common in dogs and cats.  The following sections describe the causes of megaoesophagus.

===Congenital Causes of Megaoesophagus===

===Congenital Causes of Megaoesophagus===

====Congenital Achalasia====

====Congenital Achalasia====

[[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>]]

====[[Vascular Ring Anomaly|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|<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. 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 possess such an anomaly.  Clinically significant anomalies are found most commonly in large breed dogs, particularly Irish setters and German Shepherd dogs.   

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 affected affected animals regurgitate repeatedly, lose weight and may develop aspiration pneumonia.