A break in the continuity of the diaphragm allows protrusion of abdominal viscera into the thorax.
In small animals, automobile-related trauma is a common cause of diaphragmatic hernia, although congenital defects of the diaphragm may also result in herniation (eg, peritoneopericardial hernia). In horses, diaphragmatic hernia may occur, less commonly, congenitally or after trauma, dystocia, or recent strenuous activity. Diaphragmatic hernias are extremely rare in cattle.
The signs vary, depending on the duration and species affected. Dogs and cats are characteristically dyspneic in the acute case. The degree of dyspnea may vary from subclinical to incompatible with life, depending on the amount of herniated viscera. If the stomach is herniated, it may bloat and the animal may deteriorate rapidly. In chronic cases, systemic signs such as weight loss may be more prominent than respiratory signs. Physical examination findings may include the absence of lung sounds and/or the presence of GI sounds on auscultation of the thorax. Congenital peritoneopericardial hernia is most frequently an incidental finding, although findings may be related to the respiratory or GI systems or due to compromised venous return to the heart. Horses most frequently present with acute, severe colic secondary to displaced intestines, or with respiratory signs and dyspnea. In cattle and water buffalo, diaphragmatic hernias may be associated with traumatic reticulitis and herniation of the reticulum.
Careful physical examination, including auscultation and percussion, usually suggests the presence of thoracic disease. The definitive diagnosis is most frequently made from radiographs. Loss of diaphragmatic contour, abdominal viscera in the thorax, and displacement of viscera from the abdomen may be apparent. Radiographic contrast studies may be necessary to make the diagnosis. Barium may be given by mouth (GI series), or water-soluble contrast may be injected intraperitoneally (celiogram). Radiographs may be difficult to obtain in horses and cows; ultrasonography is useful. Samples from abdominocentesis and thoracocentesis, electrocardiographs, and blood work may be obtained, and surgical exploration of the abdominal cavity may be necessary for definitive diagnosis in these species.
Surgical repair of the hernia is the preferred treatment. Other areas of trauma may be present. Optimally, the animal should be stabilized before surgery. If the diaphragmatic tear is chronic, it is necessary to be especially careful with anesthesia, because reexpansion pulmonary edema is likely fatal.