(Also been called chalasia, achalasia, megalo-oesophagus, oesophageal paralysis)

Note for Pet Owners:

This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

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Megaoesophagus means dilation of the oesophagus (gullet). This can be identified on plain (survey) Xrays or on contrast radiography - particularly following a barium swallow.


There are many potential causes of megaoesophagus including congenital abnormalities which may or may not be hereditary, neuromuscular disorders, obstructions of the oesophagus ( e.g. foreign bodies, vascular rings, cancer), toxic causes (e.g. lead ) and others (e.g. hypothyroidism, Addisons disease) . Persistent right aortic arch  is a common congenital vascular ring abnormality which occurs at the base of the heart, and has been confirmed to be inherited in the German Shepherd Dog

Achalsia  is not now thought to be a common cause of idiopathic megaoesophagus in animals and as yet unidentified disorders of the neuromuscular system are thought to be the most likely cause in most cases. This is based upon the observation that loss of motor function is definitely present.

Causes of secondary megaoesophagus include any condition which can interfere with neuromuscular function (e.g. myositis, myopathy, neuromuscular transmission, neuropathies.

Breed Occurrence

Megaoesophagus is the main cause of regurgitation in both dogs and cats. In veterinary referral centres about 1/1000 cases has this condition.

In young animals idiopathic megaoesophagus is known to be inherited * in Wirehaired Fox Terriers (simple autosomal recessive) and in Miniature Schnauzers (simple autosomal dominant or 60% penetrance autosomal recessive).

The following Breeds are predisposed to develop idiopathic megaoesophagus at an early age, and the condition may be congenital and/or genetically inherited* :

German Shepherd Dogs, Great Danes, Greyhounds, Newfoundlands, and  

Abyssinian and Siamese Cats


There are two distinct forms of megaoesophagus separated by age :

    1. Congenital megaoesophagus - present at birth and identified soon after weaning
    2. Acquired megaoesophagus - can develop at any age, due to a variety of causes.

Animals with megaoesophagus are unable to transport the food that they swallow from the pharynx to the stomach. As a result food material and saliva accumulates in the oesophagus until it is eventually passively regurgitated. This often occurs soon after feeding, and usually the animal holds it's head down and appears to "cough up" a sausage shaped ball of food. The animal coughs due to stimulation of the laryngeal protective reflexes as the food passes forwards from the oesophagus into the pharynx. Megaoesophagus is frequently diagnosed in young animals when they start to show signs soon after weaning from milk to solid foods.

One serious complication of megaoesophagus is the high risk of inhalation pneumonia because the animal does not know when it is about to regurgitate food and may inhale food before the laryngeal reflexes close off the airway. This is in contrast to vomiting in which the animal is aware that it is going to eject food from the stomach and the larynx closes off the entrance to the trachea in advance.

In cases with inhalation, coughing  or dyspnoea


Xrays to confirm the presence of a dilated oesophagus, and in some cases for evidence of secondary inhalation of food material. Dilation of the oesophagus with air or food material can be seen on plain radiographs

The plain Xray below shows food accumulation in the oesophagus, with dilation due to air, and displacement of the wind-pipe (trachea) which is pushed down (ventrally) by the large oesophagus.

The use of contrast studies is very helpful to clearly demarcate the inner lining of the walls from the lumen contents and surrounding soft tissue structures. 

Positive contrast material (such as barium or iodine preparations show up on XRay images as solid white. Negative contrast materials such as air or other gases show up as black.In megaoesophagus contrast materials eg a barium swallow are  retained in the oesophagus.

The XRay  below shows white contrast material (barium) retained in the oesophagus

In the XRay below liquid barium has been given and, following regurgitation it has been inhaled into the lungs giving a clear outline of both the oesophagus and the bronchial tree (called a bronchogram when performed deliberately).. This clearly indicates the functional difficulties that these patients have when swallowing liquids and foods.


Passing an endoscope down the oesophagus is a useful diagnostic tool to identify and in some case remove obstructions in the lumen (intralumenal) or oesophageal wall (intramural).

Image intensification demonstrates abnormal peristaltic waves with asynchronous activity in the caudal segment of the oesophagus.

Idiopathic causes - there is no specific treatment, but animals can be fed from a height (e.g. the feeding bowl is placed on a table, and the dog encouraged to eat standing up on it's back legs) with soft moist foods (gruel consistency).

Secondary megaoesophagus - treat the underlying cause e.g. ligate and section constricting vascular rings (e.g. persistent right aortic arch)

Metoclopramide might help as it encourages oesophageal contractions in the distal segment, and calcium channel blockers (e.g. nifedipine) might prove useful. Antibiotics are used to treat aspiration pneumonia. Cutting the muscular wall of the oesophagus (myotomy) may be useful in some cases though it does not improve oesophageal function.

The prognosis is good for most affected animals, but poor if inhalation pneumonia develops.

Long term problems
Chronic pneumonia due to inhalation. Need to feed animals from a height.


Updated October 2013