It is understood that hiatus hernia is the result of either decreased elastin of phrenoesophageal membrane due to aging or imbalance in pressure gradient between intra-abdominal pressure and intra-thoracic pressure leading to the esophagogastric junction being displaced into normal hiatus. A rise in intra-abdominal pressure and lower thoracic pressure can cause hernia. Occasionally, esophageal shortening pulls the junction into the hiatus. This physiological shortening may occur as a normal response to swallowing. The LES is shorter and weaker in large hiatus hernia and have severe reflux symptoms and trauma. Paraesophageal hernia are less common and have lower incidence of gastroesophageal reflux disease.

• Lower esophageal sphincter (LES) is the group of smooth muscles in the distal esophagus at the gastroesophageal junction.

• LES prevents the reflux of gastric contents into esophagus.

• The mechanisms or structures preventing the reflux include:
  • Angle of His: Anhle of his is the angle between the cardia of stomach and distal portion of esophagus. It functions as a valve or flap.
  • Diaphragmatic crura
  • High LES pressure as compared to intraabdominal pressure
  • Phrenoesophageal membrane

• Phrenoesophageal ligament or membrane is fibrous elastic connective tissue arising from crura and inserts circumferentially into esophageal muscles.
• It maintains and support LES by anchoring it during peristalsis.

• The parts of diaphragm involved in the pathophysiology of the hiatus hernia include:^[2][3]
  • Crura (crus of diaphragm)
  • Esophageal hiatus (opening in diaphragm for esophagus at T10)

• It is understood that hiatus hernia is the result of either:^[4]
  • Decreased elastin of phrenoesophageal membrane due to aging^[5][6]
  • Imbalance in pressure gradient between intra-abdominal pressure and intra-thoracic pressure leading to the esophagogastric junction being displaced into normal hiatus.A rise in intraabdominal pressure and fall in intra-thoracic pressure may lead to development of hernia.^[7]
    • The causes of increased intra-abdominal pressure that may lead to hiatus hernia include:^[8]
      • Coughing
      • Vomiting
      • Heavy lifting
      • Obesity
      • Pregnancy
      • Physical strain
  • Occasionally, esophageal shortening pulls the junction into the hiatus. This physiological shortening may occur as a normal response to swallowing.^[9]The LES is shorter and weaker in large hiatus hernia and have severe reflux symptoms.^[10]
  • Trauma
• The symptoms in hiatus hernia are the result of reflux esophagitis and the mechanisms involved include:^[4]
  1. Low resting LES pressure
  2. Prolonged time taken to clear acid
  3. Delayed gastric emptying
  4. Transient LES relaxation which occurs more frequently in hiatus hernia
• The pathophysiology of hiatus hernia depends on the histological subtype:^[11]
  • Paraesophageal hernia are less common and have lower incidence of gastroesophageal reflux disease.
  • The initial clinical presentation including dysphagia, postprandial nausea and vomiting are result of impaired gastric emptying due to mechanical obstruction.
  • It enlarges with time and results in symptoms are related to the abnormal intra-thoracic location of the stomach.
  • The gastrosplenic and gastrocolic ligament are laxed.
• The hiatus hernia reduces LES sphincter.^[4]

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• Hiatus hernia is possibly transmitted in autosomal dominant to male to male inheritance pattern.^{[12][13][14][15]}
• Sliding hiatus hernia is usually sporadic but some cases have been seen following familial pattern, as do the paraoesophageal hiatus hernia.^[16]

Conditions associated with hiatus hernia include:

• Gastroesophageal reflux disease^[17]
• Esophagal ring^[18]
• Congenital diaphragmatic hernia^[12][19]
• Epiphrenic diverticula^[20]

• On gross pathology, characteristic findings of hiatus hernia include:^[18]
  • Herniated portion gets dilated and undergo ischemic changes
  • Ischemic necrosis can be seen

• On microscopic histopathological analysis, variable chronic inflammation, ischemia and necrosis may be seen in hiatus hernia.^[18]