Diaphragmatic Hernia

The diaphragm is a sheet of muscle that separates the thoracic (chest) cavity from the abdominal cavity. It serves as a barrier between these spaces and plays a key role in breathing. A diaphragmatic hernia occurs when the diaphragm is torn or disrupted, allowing abdominal organs to move into the chest cavity. These hernias often develop after a traumatic incident, such as being struck by a vehicle, and affected animals may have multiple injuries that require medical treatment.

Two forms of diaphragmatic hernia are seen in dogs and cats:

• Traumatic — caused by an external event that tears the diaphragm.
• Congenital — present at birth. (The most common congenital subtype is the peritoneal-pericardial diaphragmatic hernia, PPDH.)

A diaphragmatic hernia can lead to marked breathing difficulty. The traumatic event responsible for the hernia may also cause rib fractures, lung lacerations, and pulmonary contusions (bruising). These injuries can result in pneumothorax (air in the chest cavity outside the lungs) or hemothorax (blood within the chest cavity). If abdominal organs have shifted into the chest, lung expansion may be further restricted. In addition, organs that have moved through the diaphragmatic defect may suffer reduced blood supply.

Clinical signs in an acute diaphragmatic hernia are typically related to impaired lung expansion due to the added contents within the chest. Observed signs include:

• difficulty breathing
• rapid, shallow breathing
• an abnormal breathing stance with the head and neck extended

If the initial injury is survived without immediate diagnosis, the hernia may be identified later in life. Over time, displaced abdominal organs—such as the liver or intestines—may develop adhesions within the chest cavity. In such chronic cases, pets may show signs consistent with liver or gastrointestinal disease, including vomiting or anorexia.

Figure 1. Normal chest radiograph of a dog (head to the left). The diaphragm is not sharply outlined but appears as the curved boundary separating the white abdominal structures on the right from the grey, air-filled lung fields. The oval structure centered in the lung area is the heart.

Diagnosis requires thoracic radiographs, which are also used to evaluate for additional abnormalities. In a normal animal, chest radiographs typically show a diaphragmatic line, a visible cardiac silhouette, and air-filled lung fields (Figures 1 and 2). With a diaphragmatic hernia, radiographs may show loss of the diaphragmatic line, loss of the cardiac silhouette, displacement of the lung fields, and abdominal organs present within the chest cavity (Figures 3 and 4).

Your primary care veterinarian may also recommend further imaging, including:

• abdominal and thoracic ultrasound
• contrast radiography (radiographs taken after placing contrast material in the gastrointestinal tract)
• computed tomography (CT scan)

Figure 2. Normal chest radiographs of a dog lying on its back (head beyond the top of the image). The diaphragm is the domed curve separating the white abdominal contents at the bottom from the darker grey lungs. The oval structure in the middle of the lung field is the heart.

Figure 3. Chest radiograph of a dog with a diaphragmatic hernia showing loss of the normal diaphragmatic line. The white abdominal organs overlap the heart, and the diaphragmatic curve is no longer clearly visible.

Figure 4. Chest radiograph of a dog on its back with a diaphragmatic hernia, again demonstrating loss of the normal diaphragmatic line. The white abdominal organs overlap the heart, and the diaphragmatic outline is not distinctly visible along its full length.

Surgery is the only definitive treatment for repairing a diaphragmatic hernia. Surgical correction should be performed as soon as the animal is stable enough to undergo general anesthesia. Some severely dyspneic patients cannot breathe comfortably until the displaced abdominal organs are removed from the chest cavity.

Emergency surgery is required if the stomach has herniated into the chest and becomes distended with gas, since this can prevent lung expansion and cause severe respiratory distress. In such cases, a needle may be inserted through the chest wall into the stomach to release gas and decompress it, after which surgery is performed.

Typical surgical repair is done by opening the abdomen along the ventral midline, gently returning abdominal organs to the abdominal cavity, and suturing the tear in the diaphragm. A tube may be placed to evacuate air, blood, or fluid that could accumulate in the chest cavity. Your veterinarian may refer your pet to an ACVS board-certified veterinary surgeon for this procedure.

In some animals, part of an abdominal organ (such as the liver, gallbladder, spleen, stomach, or small intestine) may need to be removed if its blood supply has been compromised. Each of these procedures carries specific risks and potential complications. If the hernia is long-standing and adhesions (scar-tissue attachments between organs) are present, bleeding may occur as a surgical complication.

Hospitalization is needed after surgery. Tubes placed during the operation—such as those used for removing fluid or for feeding—may need to remain in place for a few days. Many pets will also have additional traumatic injuries that necessitate continued inpatient care. Pain control is a major part of recovery and is generally best handled in the hospital.

Most animals start to feel better after surgery and may want to be active; however, rest should be encouraged and activity should be avoided during the postoperative period.

Prognosis for traumatic diaphragmatic hernia varies depending on the presence and severity of other injuries. It is estimated that approximately 15% of animals with traumatic diaphragmatic hernia die before reaching veterinary care. The best survival rates occur when shock is successfully treated before surgery. Animals that undergo surgery more than one year after the initial event may have a poorer outcome due to adhesions (fibrous attachments) involving other organs or tissues.

For dogs and cats undergoing surgery for congenital hernias (PPDH), the mortality rate is low, and the prognosis for returning to normal function and performance is excellent.