Hiatal hernia is a genetic disease of dogs characterized by a hernia of the anterior stomach through the diaphragm.
A hiatal hernia, which occurs more common in dogs with brachycephalic syndrome, is defined as any protrusion of abdominal contents through the oesophageal hiatus of the diaphragm into the thoracic cavity in the presence of an intact phrenico-oesophageal ligament.
Hiatal herniation was thought to be caused by a primary disturbance of the lower oesophageal sphincter, but has since been shown to be caused by an abnormality or laxity in the phrenico-oesophageal ligament that allows excessive movement of the oesophagus, gastro-oesophageal junction, gastric cardia and other abdominal organs.
Four types have been described in the dog:
- Type I (sliding, axial or oesophageal) - most common in Shar Pei, British Bulldog and Chow Chow - axial displacement of the distal part of the oesophagus, the gastro-oesophageal junction and part of the stomach through the oesophageal hiatus into the thoracic cavity
- Type II (rolling or paraoesophageal) - distal segment of the oesophagus and lower oesophageal sphincter remain in a fixed position but a portion of the fundic region of the stomach herniates into the mediastinum alongside the thoracic oesophagus
- Type III - rare - mixture of types I and II
- Type IV - rare - type III complicated by the stomach or other abdominal viscera being located in the paraoesophageal sac.
It is important to differentiate between the types of hiatal hernia because the underlying pathology and pathophysiology are different, necessitating different treatments.
Clinically affected dogs are often young, or have a long history of vague gastrointestinal signs including regurgitation, coughing, anorexia, dyspnea and ptyalism as a result of reflux esophagitis.
Secondary aspiration pneumonia is not uncommon, and in rare cases, rupture or strangulation of the short gastric vessels lead to the formation of a hemorrhagic pleural effusion that causes acute severe dyspnea.
Radiographic and CT imaging usually reveals a soft tissue opacity in the caudodorsal thorax as well as varying degrees of pleural effusion. A barium meal swallow may be required to highlight barium in the distended region anterior to teh diaphragm. Fluoroscopy and esophagoscopy are additional ancillary tests available to assist in procuring a diagnosis.
A definitive diagnosis usually requires an exploratory celiotomy to confirm the presence of herniation of the gastric cardia, fundus, and body through the esophageal hiatus and an adjacent, distinct defect in the diaphragm.
In most cases, surgical correction of the hernia is required, usually involving surgical reduction of the hernia followed by plication of the oesophageal hiatus, oesophagopexy and left flank gastropexy.
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