Is it megaesophagus or a normal variation?

Is it megaesophagus or a normal variation?

Aug 01, 2008

Allison Zwingenberger
Megaesophagus is a condition in which the esophagus has reduced peristalsis, and has poor tone at rest. The esophagus can have a mild, focal motility problem, or the entire organ may be dilated and functioning poorly.

These varations in severity mean that megaesophagus can have a variety of radiographic appearances. Both focal and generalized megaesophagus can be congenital, or acquired secondary to inflammation, foreign bodies, neuromuscular disease or idiopathic causes. Since a radiograph is a snapshot in time of the dynamic process of swallowing, it can be hard to decide what is a variation of normal, and what qualifies as an esophageal motility problem.

Variations of normal

Image 1: The cricopharyngeus muscle is outlined by air in the cervical esophagus.
There are variations in the normal appearance of the esophagus one should recognize. The first is a small amount of air in the cervical esophagus, just caudal to the cricopharyngeus muscle (Image 1). It often outlines the cricopharyngeus muscle, or upper esophageal sphincter, that lies dorsal to the laryngeal cartilages (circled, Image 1). The muscle appears oval, and the air usually is triangular in shape. The cricopharyngeus sometimes gets mistaken for a foreign body because of its size. This transient accumulation of air is more common in animals under general anesthesia, but is seen in conscious radiographs as well.

Image 2: A normal, transient collection of air cranial to the heart.
The second variation of normal is a triangular pocket of air in the thoracic esophagus, just cranial to the heart base (Image 2). Small amounts of air like these should clear with the next swallow, and are usually not seen on other radiographs of the same series.

Image 3: Fluid in the caudal esophagus on a left lateral projection.
Finally, if you are taking three-view thoracic series, you'll often see some fluid in the caudal esophagus on the left lateral projection (Image 3). This is because the esophagus and cardia of the stomach are on the left, and the increased pressure from abdominal organs causes some reflux of gastric contents. The key to recognizing these variations is that they are transient. If you take another radiograph, they should be cleared.


Image 4: Generalized megaesophagus and aspiration pneumonia.
Focal or generalized megaesophagus can cause persistent accumulations of air, or larger amounts of air, to accumulate in these sites or other portions of the esophagus. The most common appearance of generalized megaesophagus is to see two diverging or parallel soft-tissue lines dorsal to the trachea and caudal vena cava, and ventral to the aorta (Image 4). The dilated portion of the esophagus might fill with fluid or food material, especially in the case of an obstructive process such as a stricture or vascular ring anomaly.

Aspiration pneumonia is a common complication of many swallowing disorders because food boluses re-enter the pharynx. Three projections of the thorax are valuable in detecting alveolar disease. The most common location for aspiration pneunomia is the right middle lung lobe (asterisk in Image 4), which you often see clearly only on a left lateral projection. The lobe is located in a ventral position, and the pneumonia often is in the most dependent portion. Subtle disease often is hidden by the mediastinum on a d/v or v/d projection, and not visible on the right lateral projection.