In mammals, the chest cavity (or thorax) is separated from the abdominal cavity by a sheet of muscle called the diaphragm. The diaphragm serves the important purpose of keeping the contents of the thorax (the lungs and heart) separate from the abdomen. It also plays a key role in the way we breathe; as the diaphragm contracts, the space in the thorax increases, leading to inhalation.
A diaphragmatic hernia is a defect in the diaphragm, such that the organs of the abdomen can protrude into the thorax, where they limit the space the lungs have to expand and therefore interfere with breathing.
Most often, diaphragmatic hernias are due to trauma, and we see them most often in dogs and cats who have been hit by a car. But diaphragmatic hernias can also occur congenitally when there is a malformation of the diaphragm. Weimaraners and Cocker Spaniels are at an increased risk for congenital diaphragmatic hernias.
Clinical signs depend on the size of the defect in the diaphragm and the extent of protrusion of the abdominal organs in the chest. Generally patients with diaphragmatic hernias have an increased respiratory effort, ranging from coughing to serious respiratory distress. When abdominal organs protrude into the chest, the lungs are compromised both by the decreased space in which to expand and by the production of excess fluid in and around the lungs as a result of inflammation.
If the tear in the diaphragm is small, it is possible for tissues from the abdomen to get trapped in the hole, where they are subject to the possibility that the local blood supply could be compromised. For instance, if a segment of small intestine slips through the hole in the diaphragm and gets trapped, the blood supply to that segment will be cut off. Without an adequate blood supply, the tissues will die, presenting an entirely different clinical picture.
Dogs or cats who have been the victim of hit by car accidents are often in shock when they present as emergencies, so sometimes the symptoms of a diaphragmatic hernia are missed. In fact, some 10 to 20% of cases of traumatic diaphragmatic hernias are not diagnosed for weeks to months after the initial trauma.
Your veterinarian may be suspicious of a diaphragmatic hernia if, during your pet’s physical exam, the lung sounds are muffled. Your veterinarian may also hear gut sounds, like gurgling, in your pet’s chest, indicating that some parts of the gastrointestinal tract are present in the thorax. Generally, pets are also displaying some kind of respiratory difficulties at the time.
Diaphragmatic hernias can usually be definitively diagnosed on x-rays, but sometimes an ultrasound will be needed in difficult cases.
The treatment for diaphragmatic hernias is surgical. The tear in the diaphragm must be repaired to prevent the abdominal organs from protruding into the chest. Patients who undergo this kind of surgery will also have a chest tube placed so that a slight negative pressure can be achieved in the chest after closure, ensuring proper breathing post-operatively.
The prognosis for patients with acute or chronic diaphragmatic hernias is good to excellent, though the sooner the condition is addressed the better. This prognosis assumes surgical repair and careful post-operative monitoring.