Megaoesophagus

Congenital Achalasia - Megaoesophagus

Megaoesophagus (Courtesy of Alun Williams (RVC))

• 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 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, vomits, eats again and vomits again because oesophagus has no tone to it.
• Oesophagus may become extremely dilated producing a megaoesophagus.
• Can affect the whole length of oesophagus.

Pathogenesis

• Appears to be due to due to delay in maturation of 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 stomach it is passed on normally.

Megoesophagus Secondary to Dextra-Aorta

Dextra-aorta (Courtesy of Alun Williams (RVC))

• Vascular rings are congenital abnormalities of the aortic arch system which interfere with oesophageal function. Normally, the aortic arch, pulmonary artery and ductus arteriosus (ligamentum arteriosum) all lie on the left side of the oesophagus.
• However, when there is anomalous development of the aortic arch, for example in the right-sided arch, the 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.

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.
  • Poisonings such as:
    • Lead
    • Tetanus
    • Botulism
  • Myopathies.

• The result is the presence of a hypotonic oesophagus in which food accumulates causing distension
• Usually the thoracic oesophagus from the thoracic inlet to the diaphragm is affected and grossly the oesophagus is dilated, thin-walled and hypotonic.