Felis ISSN 2398-2950

Congenital hernia

Contributor(s): Rachel Burrow, Jacqueline Davidson

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: hernia may be pleuroperitoneal, peritoneopericardial Peritoneal-pericardial diaphragmatic hernia (PPDH), or hiatal.
  • 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.
    This is the commonest congenital pericardial and diaphragmatic anomaly in cats.
  • 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, the associated clinical signs may occur intermittently.
    Hiatal hernia is rare in the cat.
  • 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.

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. 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 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.
  • Ventral abdominal hernia may occur with other congenital defects,
  • Most umbilical hernias are thought to be inherited, and may be polygenetic. 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 are rare and have not been shown to be heritable in the cat to date. Acquired inguinal hernias have been reported following trauma.

Pathophysiology

  • Pleuroperitoneal hernia may be 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 although this appears to be less common in cats than dogs with a herniated stomach.
  • 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 Pericardial disease, 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 Acid base imbalance, 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  Pneumonia. Signs of esophagitis include vomiting Vomiting, regurgitation Regurgitation, and hypersalivation. Decreased esophageal motility and megaesophagus Megaesophagus can occur secondary to hiatal hernia. Upper airway obstruction may exacerbate or cause clinical signs of hiatal hernia. 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 (inguinal hernia) can cause azotemia Azotemia, hyperkalemia  Hyperkalemia, and metabolic acidosis. Death can occur in 2 or 3 days if the obstruction is not relieved.

Epidemiology

  • Prevalence of most congenital hernias in cats is unknown but low.
  • In one study Persian cats had a higher prevalence of peritoneopericardial hernia, another study reported a higher prevalence within domestic long hair and Himalayan cats.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Reimer S B, Kyles A E, Filipowicz D E et al (2004) Long-term outcome of cats treated conservatively or surgically for peritoneopericardial diaphragmatic hernia: 66 cases (1987-2002). JAVMA 224 (5), 728-732 PubMed.
  • Lorinson D, Bright R M (1998) Long-term outcome of medical and surgical treatment of hiatal hernias in dogs and cats: 27 cases (1978-1996). JAVMA 213 (3), 381-384 PubMed.
  • Voges A K, Bertrand S, Hill R C et al (1997) True diaphragmatic hernia in a cat. J Vet Radiol Ultrasound 38 (2), 116-119 PubMed.
  • Wallace J, Mullen H S, Lesser M B (1992) A technique for surgical correction of peritoneal pericardial diaphragmatic hernia in dogs and cats. JAAHA 28 (6), 503-510 VetMedResource.
  • Mann F A, Aronson E, Keller G (1991) Surgical correction of a true congenital pleuroperitoneal diaphragmatic hernia in a cat. JAAHA 27 (5), 501-507 VetMedResource.
  • Hay W H, Woodfield J A, Moon M A (1989) Clinical, echocardiographic, and radiographic findings of peritoneopericardial diaphragmatic hernia in two dogs and a cat. JAVMA 195 (9), 1245-1248 PubMed.
  • Prymak C, Saunders H M, Washabau R J (1989) Hiatal hernia repair by restoration and stabilisation of normal anatomy. An evaluation in 4 dogs and one cat. Vet Surg 18 (5) 386-391 PubMed.
  • Waldron D R, Hedlund C S, Pechman R (1986) Abdominal hernias in dogs and cats: A review of 24 cases. JAAHA 22 (6), 817-823 VetMedResource.
  • Robinson R (1977) Genetic aspects of umbilical hernia incidence in cats and dogs. Vet Rec 100 (1), 9-10 PubMed.
  • Hayes H M (1974) Congenital umbilical and inguinal hernias in cattle, horses, swine, dogs and cats. Risk by breed and sex among hospital patients. Am J Vet Res 35 (6), 839-42 VetMedResource.
  • Frye F L & Taylor D O (1968) Pericardial and diaphragmatic defects in a cat. JAVMA 152 (10), 1507-10 PubMed.

Other sources of information

  • Hunt G B, Johnson K A (2003) Diaphragmatic, pericardial, and hiatal hernia. In: Slatter D (ed) Textbook of Small Animal Surgery, 3rd ed, pp 471-487.
  • Read R A, Bellenger C R (2003) Hernias. In: Slatter D (ed) Textbook of Small Animal Surgery, 3rd ed, pp 446-448.
  • Smeak D D (2003) Abdominal hernias. In: Slatter D (ed) Textbook of Small Animal Surgery, 3rd ed, pp 449-470.


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