The dog’s stomach is a sac-like structure designed to store large volumes of food and begin the digestive process. Once eaten, most food leaves the stomach within twelve hours after entering. The esophagus (muscular tube) carries food to the stomach, where it enters via a valve-like structure called the cardiac sphincter. On the interior surface of the stomach is a series of folds called gastric folds. These folds function to help grind and digest food. The inner stomach lining secretes acids and enzymes to break food down as the initial step in the digestive process. Once the initial stomach digestive process is complete, the partially digested food exits the stomach through the pyloric sphincter area and then enters the duodenum (small intestine).
Where the stomach empties into the duodenum, there is a circular, valve-like muscle called the pyloric sphincter. The pyloric sphincter constricts and dilates to regulate the flow of food from the stomach into the small intestine. Occasionally, for unknown reasons, the pyloric sphincter constricts or spasms, causing an abnormal narrowing (stenosis) of the entrance into the small intestine. Small breeds, especially nervous individuals, seem to develop this condition more frequently than others.
Intermittent vomiting within one to two hours of eating is the most common sign of pyloric stenosis. The food will appear undigested, pretty much looking just as it did when eaten. The sphincter may not always be constricting or spastic, therefore, some meals may pass without vomiting. Additionally, liquid diets or water will pass through the narrowed sphincter more easily than bulky foods. In severe cases, weight loss may develop.
Many dogs live normal lives with only occasional episodes of vomiting. It appears the muscular spasms are not always constant in these cases. If a dog is exhibiting severe stomach outflow restrictions from a more constant pyloric stenosis, then weight loss and even death can result.
A diagnosis is not always easy. A careful history of vomiting in relation to eating must be evaluated. Barium studies with radiographs (x-rays) may reveal the narrowed stomach outflow. Once diagnosed, surgery provides the best cure. The pyloric sphincter, being a narrow muscular band, can be surgically severed, thus eliminating the constriction. Additionally, the stomach outflow area can be surgically widened, allowing food to pass into the duodenum. The outcome after surgery is excellent.