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===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 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” prevents 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.
[[Category:Oesophagus - Pathology]]
[[Category:Oesophagus - Pathology]]