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-Less favourable if there is extensive esophageal damage
-Less favourable if there is extensive esophageal damage
==from megaoesophagus page:
[[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 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 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.
[[Category:Cardiovascular_System_-_Developmental_Pathology]]
[[Category:Cardiovascular_System_-_Developmental_Pathology]]
[[Category:To_Do_-_Cardiovascular]]
[[Category:To_Do_-_Cardiovascular]]