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When the pylorus narrows or blocks, gastric contents cannot flow effectively into the duodenum, causing the stomach to become distended. Ingested material accumulates progressively, and the stomach may eventually lose its ability to contract, further worsening the stasis and preventing normal gastric emptying.

Non-cancerous causes include chronic peptic ulcer disease causing scarring, gastric bezoars, and inflammatory bowel disease thickening the stomach wall. Cancerous causes involve direct invasion or extrinsic compression from tumors like gastric carcinoma or pancreatic adenocarcinoma pressing on the gastric outlet without invading it directly.

Repeated vomiting of undigested food leads to loss of gastric fluids containing chloride and potassium, causing hypochloremia and hypokalemia. These losses trigger metabolic alkalosis. Chronic vomiting also causes dehydration and, in patients with concurrent malignancy, can contribute to malnutrition and nutritional deficiencies.

Early in pyloric obstruction, the narrowed pylorus can still pass liquids more easily than solid food particles. However, as the obstruction worsens, even fluids accumulate in the stomach and become poorly tolerated, eventually leading to vomiting of all ingested material regardless of consistency.

Prolonged gastric content retention raises the risk of aspiration pneumonia, particularly in individuals with compromised airway protection. Chronic obstruction also causes malnutrition, especially in patients with concurrent malignancy. Dehydration and electrolyte imbalances from repeated vomiting further compromise patient health and require timely intervention.

Chronic peptic ulcer disease causes inflammation and scarring of the pyloric canal, gradually narrowing the passage between the stomach and duodenum. This progressive narrowing reduces the pylorus's ability to allow gastric contents to pass, eventually resulting in functional obstruction and impaired gastric emptying.

Timely identification of whether obstruction stems from structural causes like tumors or scarring versus functional etiologies is critical because management strategies differ significantly between these categories. Accurate diagnosis guides treatment decisions, from medical management to surgical intervention, ensuring appropriate and effective patient care.