Canine Megaesophagus Study Guide

Overview and Clinical Importance

Megaesophagus is a disorder characterized by diffuse dilation and decreased peristalsis of the esophagus, resulting in loss of the ability to move food from the mouth to the stomach. It is the most common cause of regurgitation in dogs and represents a significant topic on the NAVLE due to its clinical complexity, multiple etiologies, and management challenges.

The esophagus normally transports food boluses via coordinated peristaltic contractions initiated by the swallowing reflex. In megaesophagus, this neuromuscular function is impaired, causing food to accumulate in a flaccid, dilated esophagus. The condition can be congenital (present at birth) or acquired (developing later in life), with acquired forms being either idiopathic or secondary to underlying diseases.

Pathophysiology

Normal esophageal function depends on coordinated neuromuscular activity. The swallowing reflex initiates when food in the mouth stimulates nerves that send signals to the swallowing center in the brainstem, which triggers peristaltic contractions. In dogs, the esophagus is composed entirely of striated muscle (unlike cats, which have smooth muscle in the distal third), making innervation by the vagus nerve critical for function.