Hiatal Hernias are classified as either sliding or parasophageal hernias, based on the relationship of the cardia to the diaphragm and herniated portion of the stomach. Around 99% of all hiatal hernias are sliding, with 1% being parasophageal hernias. A parasophageal hernia is considered to be a potential life threatening condition due to the risk of volvulus, incarceration or strangulation.
A sliding hiatal hernia occurs when the phrenoesophageal membrane stetches or ruptures, allowing the proximal portion of the stomach to herniate through the esophageal hiatus of the chest diaphragm. Prevalence increases with age and is thought to be the result of progressive wear and tear. Roughly 10% of the adult population in N America have a hiatal hernia.
Large hiatal hernias are not only associated with more severe GERD, but also with diminution of LES pressure. This decrease in pressure may result from displacement of the LES proximally into the chest as the hiatal hernia moves through the diaphragm. As a result, the LES loses its crural diaphragmatic component an important factor in generating some of the sphincter pressure.
The radiographic diagnosis can be made on single or double contrast barium esophogeal swallowing studies. A sliding hiatal hernia can be diagnosed when either a mucosal ring is seen 2+cm above the diaphragmatic hiatus or gastric folds are seen within the hernia extending 2+cm above the esophageal hiatus.