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
Causes of secondary megaoesophagus include any condition which can interfere with neuromuscular function (e.g. myositis, myopathy, neuromuscular transmission, neuropathies.
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).
German Shepherd Dogs, Great Danes, Greyhounds, Newfoundlands, and
Abyssinian and Siamese Cats
There are two distinct forms of megaoesophagus separated by age :
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.
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.
Long term problems
Updated October 2013