The diaphragm is a dome-shaped sheet of muscle that separates the chest cavity (containing the heart and lungs) from the abdominal cavity below it. To allow necessary physiological systems to pass between these two regions, the diaphragm contains several openings. These apertures allow structures like major blood vessels and the digestive tract to connect the upper and lower halves of the torso.
Anatomy: Defining the Esophageal Hiatus
The esophageal hiatus is an opening within the diaphragm, typically elliptical or oval in shape. It is situated in the muscular portion of the diaphragm, generally positioned at the level of the tenth thoracic vertebra (T10). The opening is formed primarily by the muscle fibers of the right crus, a tendinous structure connecting the diaphragm to the spine.
The right crus typically divides into two bundles that loop around the esophagus, forming the boundaries of the hiatus. This arrangement ensures the opening is not a rigid hole but a dynamic muscular ring that responds to movement and pressure changes. The muscle fibers cross over inferiorly, providing a sling-like mechanism around the digestive tube.
Normal Function and Associated Structures
The primary structure passing through the esophageal hiatus is the esophagus, the tube connecting the throat to the stomach. The opening also transmits the anterior and posterior vagal trunks, which regulate digestive processes. Small esophageal branches of the left gastric blood vessels and lymphatic vessels also travel through this aperture.
The muscle fibers of the crura surrounding the esophagus act as a physiological sphincter, functioning like a valve. This muscular compression maintains the pressure gradient between the chest and abdominal cavities. Since abdominal pressure is higher than chest pressure, this closure helps prevent stomach contents from moving backward into the esophagus. This action is particularly important for preventing reflux during swallowing or when abdominal pressure rises.
When the Hiatus Fails: Hiatal Hernias
A hiatal hernia occurs when the muscular opening of the esophageal hiatus widens or weakens, allowing part of the stomach to protrude upward into the chest cavity. This failure to maintain the necessary seal and support often results from aging or activities that cause chronic increases in abdominal pressure, such as persistent coughing, heavy lifting, or obesity.
The most common type, accounting for approximately 95% of cases, is the sliding hiatal hernia (Type I). In this scenario, the gastroesophageal junction slides up into the chest cavity through the widened hiatus. This displacement compromises the function of the lower esophageal sphincter, making it less effective at preventing stomach acid from backing up. This often leads to symptoms like heartburn and regurgitation.
A less common but sometimes more serious form is the paraesophageal hiatal hernia, which includes Type II, Type III, and Type IV hernias. The Type II hernia, sometimes called a rolling hernia, involves a portion of the stomach’s upper section (the fundus) pushing up through the hiatus alongside a normally positioned gastroesophageal junction.
Small hernias are often unnoticed, but when symptoms occur, they are typically related to gastroesophageal reflux disease (GERD), including a burning sensation in the chest and difficulty swallowing. In paraesophageal hernias, the displaced stomach tissue may become trapped or twisted. This presents a higher risk of complications and can cause symptoms like chest pressure or pain.