Gastrointestinal Imaging

Hernia, hiatal

hernia classified either as sliding or paraoesophageal depending on the relationship of the cardia to the diaphragm and herniated portion of the stomach. About 99% of all hiatal hernias are sliding and the remaining 1% are paraoesophageal. Although rare, a paraoesophageal hernia unlike a sliding hernia, is potentially life threatening. This is due to the risk of volvulus and incarceration of the hernia.

Sliding hiatal hernia

Normally, the phreno-oesophageal membrane surrounds the gastro-oesophageal junction and fixes the distal oesophagus to the diaphragm thereby preventing the stomach from herniating through the oesophageal hiatus into the thoracic cavity. When the phreno-oesophageal membrane is insufficient an axial hernation of the stomach into the chest cavity may occur (Fig.1).

In these circumstances, the cardia will be situated above the diaphragm. The prevalence of hiatal hernia increases significantly with age and has been estimated to be present in about 10% of the adult population. When the lower oesophageal sphincter is located in the thoracic cavity it is not reinfored by the diaphragmatic crus and the surounding tissues. The lower oesophageal sphincter (LES) as such is not strong enough to hinder gastro-oesophageal reflux. Therefore, a hiatal hernia is a common finding in patients with a gastro-oesophageal reflux disease (GERD). However, most patients with a hiatal hernia do not have GERD. The differentiation between a normal ampulla of the distal oesophagus and a true hiatal hernia is not clearcut. The best way of localizing the LES is by manometry which preferably should be done at the same time as fluoroscopy in order to exactly localise the sphincter in relation to the diaphragm. Manometrically, differentiation between the abominal and thoracic cavity is achieved by observing pressure changes during breathing.

A prone single contrast barium swallow is more likely to demonstrate sliding hernia than upright double contrast studies. A hiatal hernia can often be recognized by the presence of gastric folds within the hernia. On double contrast examinations areae gastricae can also be seen within the hernia. A hiatal hernia may cause deformity of the oesophagus and/or fundus of the stomach; appearances that may lead to unnecessary endoscopic procedures.

Paraoesophageal hernia

True paraoesophageal hernias are uncommon. The cardia is in a normal position below the diaphragm while a portion of the stomach herniates through a defect in the phreno-oesophageal membrane into the thoracic cavity (Fig.2).

There is a distinct subgroup of paraoesophageal hernias that are often observed in young persons and seem to be due to a congenital defect. These are characteristically located to the right of the distal oesophagus where a portion of the gastric fundus protrudes into the thoracic cavity. These are prone to incarcerate and cause symptoms of intermittent epigastric pain.

OE

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Fig.1

Sliding hiatal hernia (arrows). The hiatus through the left hemidiaphragm is wide open (arrowhead).
Hernia, hiatal, Fig.1
Hernia, hiatal, Fig.2