Diaphragmatic hernia

What it is

A diaphragmatic hernia is the passage of abdominal organs into the thorax through a defect in the diaphragm. In the dog most are traumatic: a sudden blow to the abdomen, typically a vehicle accident, raises the abdominal pressure while the glottis is open, and the diaphragm tears, usually in its muscular part. The liver is the organ most often herniated, followed by the small intestine, stomach, spleen and omentum. The herniated organs, together with pleural effusion, reduce lung expansion.

The main congenital form is the peritoneopericardial diaphragmatic hernia, in which the abdominal cavity communicates with the pericardial sac; it is a different condition, often found incidentally, and the Weimaraner is overrepresented.

Who it affects

Dogs of any age and breed after blunt trauma. Some are not diagnosed until weeks, months or even years later, when respiratory or digestive signs appear.

Anatomy involved

The diaphragm (diaphragma) is a dome-shaped musculotendinous sheet between the thoracic and abdominal cavities. Its centre is the central tendon (centrum tendineum), and its muscular periphery has a lumbar part (the right and left crura, attached to the lumbar vertebrae), a costal part attached to the ribs and costal arch, and a sternal part. It has three openings: the aortic hiatus, the oesophageal hiatus and the foramen of the caudal vena cava. It is innervated by the phrenic nerves, formed from the caudal cervical spinal nerves (C5–C7). Traumatic tears are usually circumferential, near the costal attachments, or radial in the muscular part.

Clinical signs

Dyspnoea and tachypnoea, exercise intolerance, shock in acute cases, muffled heart and lung sounds, borborygmi heard over the thorax and an abdomen that feels "empty" on palpation. Chronic hernias may cause vomiting, weight loss or intermittent dyspnoea. A herniated stomach that fills with gas is a life-threatening emergency.

Diagnosis

• Thoracic radiographs: loss of the diaphragmatic outline, gas-filled bowel or stomach in the thorax, displacement of the heart and lungs, pleural effusion.
• Ultrasound to show abdominal organs next to the heart and a discontinuous diaphragm.
• Positive-contrast gastrointestinal study or CT in unclear cases.

Treatment

Surgical repair through a ventral midline coeliotomy: the organs are returned to the abdomen, the edges of the defect are debrided if needed and sutured, and air is removed from the pleural space at the end of surgery. The patient is stabilised first (oxygen, treatment of shock, thoracocentesis), except when a herniated stomach is distending, which requires immediate decompression and surgery. In chronic hernias adhesions are common, and the collapsed lung must be re-expanded slowly to avoid re-expansion pulmonary oedema. Dogs that survive the perioperative period usually do well.

In the cat

Traumatic diaphragmatic hernias are common in cats after road traffic accidents and falls from height, with the same consequences as in the dog; many cats compensate well and are diagnosed weeks or months later, when dyspnoea, vomiting or exercise intolerance appears. Dyspnoeic cats must be handled very carefully and stabilised with oxygen before any test.

Peritoneopericardial diaphragmatic hernia is the most common congenital pericardial anomaly in the cat. Long-haired breeds such as the Persian, Himalayan and Maine Coon are overrepresented. Many are found incidentally on radiographs taken for other reasons: a large, rounded cardiac silhouette with overlap of the caudal heart border and the diaphragm, and sometimes intestinal gas within the pericardial sac; ultrasound confirms the diagnosis. Cats with digestive or respiratory signs undergo surgery, while cats without signs can do well without it.

Key studies in the cat

Traumatic hernia

• Schmiedt et al. (2003), 34 cats treated surgically. Mean age was 3.6 years and 50% had postoperative complications, mostly tachypnoea and dyspnoea. Mortality was associated with older age, concurrent injuries and, strikingly, lower respiratory rates on admission; it was not associated with how long the hernia had been present.
• De Bastiani et al. (2023), 90 cats repaired with intraoperative transdiaphragmatic thoracocentesis and no chest drain. Intra- and postoperative complication rates were 3.3% and 12.4%, and survival was 93.3%. Comorbidities, emergency surgery and older age were associated with worse long-term survival. There is no comparison group, and it was published in an open-access journal of modest impact.

Peritoneopericardial hernia

• Reimer et al. (2004), 67 cats. Domestic longhair and Himalayan cats were overrepresented, and in 27 cats the hernia was an incidental finding. Of 66 cats treated, 37 had surgery (postoperative mortality 14%, with mostly minor complications) and 29 were managed conservatively; in 2 of 22 conservatively managed cats, signs progressed to need surgery or caused death.
• Banz and Gottfried (2010), 31 cats and 8 dogs treated surgically. Long-haired cats, particularly Maine Coons, appeared to be at higher risk, and respiratory signs predominated in cats. The liver, gallbladder and small intestine were the organs most often herniated, and perioperative mortality was low.
• Burns et al. (2013), 30 cats and 28 dogs from two hospitals. Prevalence in cats was 0.062%, and half of the cats were incidental findings. Surgery resolved the signs in 85.3% of the animals operated on, and long-term survival did not differ between surgical and conservative treatment. Treatment was chosen according to signs, not at random.