Introduction

• A congenital hernia is a defect in the abdominal wall or diaphragm that is present at birth. Abdominal organs or other abdominal tissue may displace through the defect.
• A true hernia has a hernia sac (peritoneum) surrounding the contents. A true hernia is usually the result of a congenital weakness in the abdominal wall.
• True hernias are often reducible (ie contents can move freely between hernia sac and abdomen), because the hernia sac reduces adhesion formation.
• A false hernia has no hernia sac and is usually acquired from trauma or previous surgery. False hernias are more likely to have adhesions that can cause incarceration (ie hernia contents are not able to be moved back into the abdominal cavity).
• The contents of the hernia are said to be strangulated when its blood supply is compromised.
• Congenital diaphragmatic hernias Diaphragm: traumatic hernia may be pleuroperitoneal, peritoneopericardial Peritoneal-pericardial diaphragmatic hernia (PPDH) , or hiatal Hiatal hernia.
  • Pleuroperitoneal hernia is a defect in the dorsolateral diaphragm with herniation of abdominal viscera into the thoracic cavity. The defect may involve absence of 1-2 cm in the left crus, or the defect may be in both crura and parts of the central tendon. Pleuroperitoneal hernia is rare.
  • Peritoneopericardial hernia occurs with improper development of the transverse septum that allows herniation of abdominal viscera into the pericardial sac.
  • Hiatal hernia is protrusion of abdominal organs through the esophageal hiatus of the diaphragm into the thoracic cavity. Sliding hiatal hernia involves the abdominal section of esophagus, the esophagogastric junction, and part of the stomach moving through the esophageal hiatus. Herniated tissues may move in and out of the thorax with changes in pleuroperitoneal pressure gradient. With paraesophageal hernia, the esophagogastric junction remains in normal position, but the fundus and various portions of the stomach move through the esophageal hiatus alongside the esophagus. Pure paraesophageal hiatal hernia is rare, but may be combined with a sliding hernia. Sliding hernia alone is most common. Hiatal hernias are uncommon, and usually occur intermittently.
• Congenital abdominal wall hernias Intestine: strangulated obstruction (hernia) occur on the cranial ventral midline (often associated with peritoneopericardial hernia), at the umbilicus, or in the inguinal region Inguinal hernia.
  • Omphalocele is a large midline umbilical and skin defect that permits abdominal organs to protrude from the abdomen. The abdominal organs are covered with amniotic tissue, until minor trauma ruptures this transparent membrane and results in evisceration.
  • Gastroschisis is a congenital abnormality similar to omphalocele, but the abdominal wall defect is paramedian.
  • A true inguinal hernia may be indirect or direct and both are uncommon. Indirect inguinal hernia, (the more common of the two), occurs when tissue protrudes through the evagination of the vaginal process in females or the vaginal tunica in males (it is also called a scrotal hernia in males). Direct inguinal hernia involves herniation of tissue through the inguinal rings, adjacent to the normal evagination of the vaginal process or vaginal tunica. Direct inguinal hernias are usually large and do not incarcerate organs.

Print off Hernias in dogs (diaphragmatic) Owner Factsheet and Hernias in dogs (umbilical and inguinal) Owner Factsheet to give to your client.

Pathogenesis

Etiology

• Congenital hernias occur when there is abnormal fetal development. The reason for this may be genetic (hereditary) or may be due to other factors, such as teratogenic agents.
• Pleuroperitoneal hernia involves incomplete development or failure of fusion of the pleuroperitoneal membrane across the pleuroperitoneal canal during development. It is thought to have an autosomal recessive mode of inheritance.
• Peritoneopericardial hernia is usually congenital. In one report a teratogenic agent was suspected as a cause of hernia in a litter of Collie puppies. It is not known if it is heritable. Peritoneopericardial hernia may occur with other congenital abnormalities including sternal defects, cranial midline abdominal wall hernia, umbilical hernia, abnormal hair swirl pattern on ventral midline, ventricular septal defect Ventricular septal defect or other cardiac defect, and pulmonary vascular disease. These combinations of congenital abnormalities are due to accidents of embryogenesis rather than inheritance.
• Hiatal hernia is usually congenital but may occur with trauma or severe respiratory distress. Trauma may damage diaphragmatic nerves and muscles, resulting in hiatal laxity. In patients with upper respiratory obstruction, reduced intrathoracic pressure during inspiration may contribute to esophageal reflux and visceral herniation. Hiatal hernia has also been reported with tetanus Tetanus. Dogs with congenital hiatal hernia usually have signs before 1 year of age.
• Ventral abdominal hernia, including umbilical hernias, may occur with cryptorchidism Testicle: cryptorchidism , and other congenital defects including: incomplete sternal fusion, diaphragmatic hernia, cardiac defects, portosystemic shunts Congenital portosystemic shunt (CPSS) , bladder exstrophy Bladder: exstrophy , hypospadias Hypospadia , and imperforate anus Anus: atresia.
• Most umbilical hernias are thought to be inherited, and may be polygenetic. Umbilical hernia has been associated with fucosidosis Storage disease , an inherited (autosomal recessive) neurovisceral lysosomal storage disease. Acquired causes of umbilical hernia are uncommon and usually due to excessive traction on the umbilical cord at parturition, or severance of the cord too close to the abdominal wall.
• Inguinal hernias have been shown to be heritable in the Basenji, Golden retriever, Cocker spaniel and Dachshund. It is polygenetic in Cocker spaniels and Dachshunds. Some congenital inguinal hernias may regress spontaneously by 12 weeks of age. Acquired inguinal hernias are most common in the middle-aged, estral or pregnant bitch, suggesting hormonal involvement. Trauma and obesity are other predisposing factors for acquired inguinal hernias.

Pathophysiology

• Pleuroperitoneal hernia is rapidly fatal if the stomach, spleen, and small intestine herniate through the left dorsolateral diaphragmatic defect. Animals are dead at birth, or develop cyanosis and dyspnea and die soon after birth. Compression and atelectasis of lung lobes by the hernia can cause hypoventilation, ventilation/perfusion mismatch Ventilation-perfusion mismatching , and hypoxia. Bloating of the stomach within the thoracic cavity can compress the lungs, leading to respiratory insufficiency and death.
• Peritoneopericaridal hernia may cause no dysfunction, and these animals are asymptomatic. The most commonly herniated organ is the liver. Falciform ligament, omentum, spleen, small intestine, and (rarely) stomach may also herniate into the pericardial sac. Pathologic changes are related to which abdominal organs are entrapped or compromised.
  • Incarceration of the liver in the pericardial sac can cause hepatic venous stasis, hepatic necrosis, biliary tract obstruction and jaundice. The resulting extravasation of fluid results in pericardial effusion, ascites, or a combination of both.
  • Effusion or the presence of viscera in the pericardial sac can cause cardiac tamponade with signs of right-sided heart failure (due to interference in venous return.)
  • Compression by the hernia can reduce lung expansion and cause respiratory insufficiency. The severity of compromise depends on the volume and rate of expansion of the herniated tissue.
  • Incarceration of the intestine can cause partial or complete obstruction to passage of ingesta. Obstruction of the stomach or proximal small bowel can cause vomiting with subsequent dehydration, metabolic alkalosis, electrolyte disturbances, and altered cardiac electrical conduction. Compromise of blood supply to the bowel can cause ischemic necrosis, intestinal perforation, and abscessation.
  • Herniation of the stomach is rare, but could result in gastric bloating or signs of gastric obstruction.
  • Peritoneopericaridal hernia has been implicated as a cause of pericardial cyst formation.
• Hiatal hernia primarily causes problems related to gastroesophageal reflux, such as esophagitis Esophagitis and aspiration pneumonia Lung: aspiration pneumonia. Signs of esophagitis include vomiting, regurgitation, and hypersalivation. Decreased esophageal motility and megaesophagus Megaesophagus can occur secondary to hiatal hernia. Upper airway obstruction may exacerbate clinical signs of hiatal hernia as demonstrated by the association of hiatal hernia and bull dogs with severe signs of brachycephalic obstructive airway syndrome and a Labrador-cross dog that had complete remission of clinical signs of hiatal hernia after surgical treatment of laryngeal paralysis Larynx: paralysis. A large hiatal hernia could contain spleen, liver, and intestine, and could interfere with cardiorespiratory function.
• Abdominal wall hernias (ventral midline, umbilicus, or inguinal) have varying pathophysiology depending on what tissue has herniated and whether it is incarcerated. In general, very large or very small hernias appear to have a lower risk of incarceration.
  • Herniation of a liver lobe, spleen or omentum rarely causes major problems unless strangulation occurs. Strangulation may be caused by constriction of the blood supply at the hernia ring or torsion of a vascular pedicle. Strangulation results in arterial and/or venous occlusion, which causes tissue ischemia and necrosis. Early venous obstruction causes organ engorgement and can result in arterial stagnation. Arterial stagnation or obstruction causes rapid organ necrosis if collateral blood supply is insufficient.
  • Obstruction of the bowel can cause electrolyte, acid-base, and fluid imbalances, which may lead to shock Shock. Strangulated hollow organs may cause loss of body fluids by sequestration. Bacteria and toxins can be absorbed systemically, causing septicemia Shock: septic or shock. Strangulated bowel may also rupture, leading to loss of blood or body fluids and septicemia.
  • Obstruction of the bladder Bladder: herniation (inguinal hernia) can cause azotemia Azotemia , hyperkalemia Hyperkalemia , and metabolic acidosis Acid base imbalance. Death can occur in 2 or 3 days if the obstruction is not relieved.
  • Scrotal hernias are associated with an increased risk of testicular tumors Testicle: neoplasia.
  • With acquired inguinal hernias, the uterus is often herniated in intact females. Clinical signs may not be apparent until pregnancy or pyometra develop.

Epidemiology

• Prevalence of umbilical hernia is about 0.2%.
• Prevalence of inguinal hernia is about 0.04%.
• Occurrence of omphalocele is unknown because puppies may die or be destroyed without veterinary care.

Diagnosis

Treatment

Prevention

Outcomes