The Gastrointestinal Tract (GIT) begins with the oesophagus (swallowing tube). The oesophagus lies within the chest, while the stomach lies within our abdominal cavity. A muscle known as the diaphragm separates the two organs. The oesophagus continues through an opening in the diaphragm, also known as the hiatus, into the stomach. A hiatal hernia occurs when there is a weakness of the hiatal muscles and the stomach bulges up into the chest through the hiatus.

There are two main types of hiatal hernias:

1. Sliding hiatal hernia
In a sliding hiatal hernia, the upper part of the stomach and the lower part of the oesophagus slides up into the chest through the hiatus, along the direction of the oesophagus. This is the most common type of hiatal hernia and accounts for about 95% of all hiatal hernias.

2. Paraoesophageal hiatal hernia
In a paraoesophageal hiatal hernia, the upper portion of the stomach moves up into the chest, through the hiatus, to lie alongside the oesophagus, and can twist more easily. This is a much rarer form of hiatal hernia but it may be more dangerous as the blood supply to the stomach may be cut off when there is twisting of the herniated stomach, which can lead to serious complications such as gangrene of the stomach and perforation.