A hiatal hernia occurs when the esophageal hiatus of the diaphragm widens, creating a hernia cavity that can contain abdominal cavity contents, most typically the stomach. In larger hernias, parts of the large and small bowel can herniate through the esophageal hiatus.

Hiatal hernias are typically asymptomatic. On occasion, patients will complain of vague abdominal discomfort. However, in most instances, they are diagnosed incidentally on cross-sectional imaging or upper endoscopy.

Hiatal hernias are classified as sliding or paraesophageal:

• Type I: sliding hernia – Most common type, due to progressive weakening of the gastroesophageal junction allowing a portion of the gastric cardia to slide upward with increased abdominal pressure, swallowing, and respiration. Patients with type I hernias are more likely to have gastroesophageal reflux disease (GERD).
• Types II, III, IV: paraesophageal hernia – Herniation includes viscera other than the gastric cardia, including gastric fundus and the colon. In type II and III hernias, the stomach becomes "inverted," possibly leading to gastric volvulus.