Which condition is characterized by the stomach’s opening thickening and blocking food entry?

Pyloric stenosis is characterized by the thickening of the pyloric opening, which is the passage between the stomach and the small intestine. This condition typically leads to a narrowing that obstructs food from passing through and can result in severe vomiting. It most commonly affects infants and is often associated with projectile vomiting shortly after feeding, dehydration, and weight loss.

The other conditions do not involve the pylorus or the blockage of food entering the digestive tract in the same manner. Intussusception occurs when a part of the intestine telescopes into an adjacent segment, leading to obstruction but not specifically involving the stomach's pyloric opening. Gastroesophageal reflux disease (GERD) is related to the backward flow of stomach contents into the esophagus, causing discomfort but not a blockage of food entry at the pylorus. Malabsorption syndrome refers to the body's inability to absorb nutrients from food properly, which is not a structural blockage but rather a functional issue. Thus, the specific thickening and blockage at the pyloric opening is what clearly defines pyloric stenosis.