Diaphragmatic Hernias

Introduction

Diaphragmatic hernias can be congenital or traumatic in origin, and acute or chronic in duration. Animals with acute traumatic diaphragmatic hernias have typically sustained significant blunt vehicular trauma. The degree of respiratory compromise depends on the amount of abdominal viscera displacement and the presence and severity of other thoracic injuries. Animals may display respiratory distress, tachypnea, tachycardia, and cyanosis. Cardiac dysrrhythmias are common due to the irritation of the heart by abdominal viscera. Animals with congenital or chronic diaphragmatic herniation may be asymptomatic or have only mild increases in respiratory rate and effort.
The creation of an abdominal-thoracic pressure gradient across the diaphragm at the time of impact dictates the nature of the injury to the thorax. If abdominal pressure is greater than thoracic, a diaphragmatic tear results. Diaphragmatic tears typically occur through the muscular portion, which is the weakest part of the diaphragm. Abdominal organ displacement into the thoracic cavity depends on the location and size of the tear. Almost any organ can herniate, although the liver is the most frequent, followed by the small intestine, stomach, and spleen.

Diagnostic Imaging

Thoracic radiography may demonstrate obvious organ herniation in the thoracic cavity. Radiographic signs include loss of diaphragmatic outline and cardiac silhouette, displacement of lung fields, presence of gas filled viscera, and pleural effusion. Effusion is usually associated with liver entrapment and venous occlusion. Abdominal radiographs may demonstrate cranial displacement of abdominal organs. Identification of stomach or intestines within the thoracic cavity makes the diagnosis of diaphragmatic hernia uncomplicated. However, if there is a large amount of pleural fluid or if the soft-tissue parenchymal organs are herniated the diagnosis of diaphragmatic hernia may be less obvious. Repeating radiographs following thoracocentesis may identify herniation that was not apparent before. Performing all radiographic views (right lateral, left lateral, ventrodorsal, and dorsoventral) may shift herniated viscera and allow better visualization. Additional diagnostic imaging procedures can be used to aid confirmation of a diaphragmatic hernia. Unconventional radiographic imaging when compared with routine survey radiographs may provide valuable information. Such views include horizontal beam projection and standing ventrodorsal projections. Upper gastrointestinal positive contrast studies using orally administered barium sulfate will show the location of the stomach and intestines. Ultrasonography can also be used, although the diaphragm itself is not readily visualized even in normal animals. Rather, it is the interface between air-filled lung and hyperechoic liver that identifies the location of the diaphragm. A straightforward diagnosis occurs when there is identification of abdominal viscera next to the cardiac silhouette. Positive contrast peritoneography can also be used if suspicion of diaphragmatic herniation is high, but cannot be confirmed from the previously described studies. Water-soluble iodinated contrast media is injected into the peritoneal cavity. Translocation of the contrast into the thoracic cavity confirms disruption of the diaphragm. [...]