Canine Hernia Study Guide

Overview and Clinical Importance

Hernias are defined as abnormal protrusions of tissue or organs through a defect in the body wall. In dogs, hernias represent a significant category of surgical conditions frequently encountered in clinical practice and commonly tested on the NAVLE. Understanding the classification, diagnosis, and management of different hernia types is essential for veterinary practitioners. A true hernia consists of three components: the hernia ring (defect), hernia sac (peritoneal lining), and herniated contents.

Classification of Canine Hernias

Hernias in dogs are classified based on anatomic location and etiology. They can be congenital (present at birth), traumatic (resulting from injury), or acquired (developing over time). Hernias may also be direct (through a rent in the body wall) or indirect (through a pre-existing anatomic opening such as the inguinal or umbilical ring).

Overview of Hernia Types

Umbilical Hernia

Umbilical hernias are the most common type of hernia in dogs, occurring when the umbilical ring fails to close completely after birth. The umbilical ring normally closes as the puppy develops, but in affected animals, a defect persists allowing abdominal contents to protrude. Most umbilical hernias are congenital and suspected to be hereditary, though the exact mode of inheritance is not fully understood.

Etiology and Pathophysiology

During fetal development, umbilical blood vessels pass through the umbilical ring to provide nourishment. After birth, this opening normally closes. When closure is incomplete, a hernia forms. The hernia appears as a soft, fluctuant swelling at the umbilicus that may become more prominent when the puppy stands, barks, cries, or strains. Umbilical hernias often occur concurrently with cryptorchidism and other congenital defects.

Breed Predispositions

Breeds with increased risk include: Weimaraners, Pekingese, Basenjis, Airedale Terriers, Pointers, and Beagles. The hereditary nature suggests affected dogs should not be used for breeding.

Clinical Presentation and Classification

Size Classification and Management

Small hernias (less than 1 cm or 1/4 inch): May close spontaneously by 3-4 months of age. Can often be monitored without intervention. Often contain only fat or falciform ligament.

Large hernias (greater than 2.5 cm or 1 inch): Unlikely to close spontaneously. May contain intestinal loops. Higher risk of strangulation. Surgical repair recommended.

Diagnosis

Diagnosis is typically made on physical examination. A soft, fluctuant swelling at the umbilicus is palpated. The size of the hernia ring can be assessed after reducing the contents. Radiographs with or without contrast may be helpful for large hernias to determine if intestinal loops are present. Ultrasound can assess viability of herniated contents.

Treatment

Surgical repair (herniorrhaphy) is the definitive treatment. The procedure involves: (1) Elliptical incision around the hernia, (2) Dissection and identification of hernia sac, (3) Reduction of herniated contents, (4) Excision of redundant sac tissue, and (5) Closure of the hernia ring with sutures. Surgery is often performed concurrently with spay/neuter to minimize anesthetic events.

Inguinal Hernia

Inguinal hernias occur in the groin region where the inner fold of the rear leg attaches to the body wall. The inguinal canal is a natural opening through which the testicles descend in males and through which the round ligament passes in females. Herniation occurs when this opening enlarges, allowing abdominal contents to pass through.

Etiology

Inguinal hernias may be congenital or acquired. Congenital hernias are often hereditary. Acquired hernias are more common in middle-aged, intact female dogs, particularly during pregnancy when increased abdominal pressure can stretch the inguinal canal. Males with inguinal hernias may also have concurrent cryptorchidism.

Breed Predispositions

Breeds with increased risk: Basenji, Basset Hound, Cairn Terrier, Cavalier King Charles Spaniel, Chihuahua, Cocker Spaniel, Dachshund, Maltese, Pekingese, Poodle, Pomeranian, and West Highland White Terrier. Small breed dogs are 2.7 times more likely to be affected. Inguinal hernias are frequently bilateral - always palpate both sides.

Clinical Signs

• Soft, fluctuant swelling in the groin region (unilateral or bilateral)
• May enlarge with straining, coughing, or activity
• Pain on palpation if strangulation has occurred
• Vomiting and signs of obstruction if intestine is trapped
• Stranguria or anuria if bladder is retroflexed into hernia
• In females: may herniate gravid uterus or pyometra

Diagnosis

Physical examination: Palpate inguinal region bilaterally. Attempt reduction to assess ring size. Radiographs: May show gas-filled bowel loops or bladder in inguinal region. Contrast studies helpful if needed. Ultrasound: Assess contents and blood flow to herniated structures.

Treatment

Surgical repair is indicated for all inguinal hernias to prevent strangulation. The procedure involves reduction of herniated contents and closure of the inguinal ring. Ovariohysterectomy is recommended in intact females to prevent future uterine herniation and because the condition may be hereditary. In males, castration should be performed. Repair both sides even if herniation is only clinically apparent on one side.

Perineal Hernia

Perineal hernias result from weakening or failure of the muscular pelvic diaphragm, allowing pelvic and occasionally abdominal organs to herniate into the subcutaneous perineal region. This condition occurs almost exclusively in older, intact male dogs (7-9 years of age).

Anatomy of the Pelvic Diaphragm

The pelvic diaphragm consists of: Levator ani muscle (thin, fan-shaped muscle from pelvic symphysis to external anal sphincter), Coccygeus muscle (from ischial spine to caudal vertebrae), and External anal sphincter. These muscles together prevent abdominal organs from herniating into the perineal region.

Etiology and Risk Factors

• Androgens and prostatic enlargement: Straining from BPH weakens pelvic diaphragm
• Chronic constipation: Repeated straining damages muscles
• Neurogenic atrophy: Damage to pudendal nerve
• Hormonal imbalances: May contribute to muscle weakness
• Rectal disease: Rectal deviation, rectal diverticulum

Types of Perineal Hernias

Clinical Signs

• Soft, fluctuant swelling lateral to anus (unilateral or bilateral)
• Tenesmus and constipation (75-80% of cases)
• Dyschezia (painful defecation)
• Stranguria or anuria if bladder retroflexes into hernia (EMERGENCY)
• Altered tail carriage
• Right side more commonly affected than left; 50-66% unilateral

Diagnosis

Digital rectal examination is diagnostic - weakness of the pelvic diaphragm is palpable. The hernia defect can be felt, and rectal deviation/diverticulum may be present. Radiography and ultrasound help determine if bladder is displaced. Urinalysis and bloodwork to assess for post-renal azotemia if urinary obstruction suspected.

Treatment

Surgical repair is required. The internal obturator muscle flap technique is the gold standard with 85-90% success rate. The internal obturator muscle is transposed to reconstruct the pelvic diaphragm. Castration is ALWAYS performed concurrently to reduce prostatic size and straining. Additional procedures include colopexy (tacking colon to body wall), cystopexy (bladder to body wall), and vas deferensopexy.

Diaphragmatic Hernia

Diaphragmatic hernias result from disruption of the diaphragm allowing abdominal organs to enter the thoracic cavity. They are classified as traumatic (more common in dogs) or congenital. The most common congenital form is peritoneopericardial diaphragmatic hernia (PPDH) where abdominal organs herniate into the pericardial sac.

Traumatic Diaphragmatic Hernia

Most common cause: Blunt force trauma (hit by car is most frequent). Mechanism: Sudden increase in abdominal pressure combined with open glottis causes air-filled lungs to deflate, creating increased pressure gradient across the diaphragm. The weaker muscular portions of the diaphragm rupture. Tears may be radial (along muscle fibers) or circumferential (along rib attachments).

Clinical Signs

• Respiratory distress: tachypnea, dyspnea, orthopnea
• Muffled heart and lung sounds on auscultation
• Borborygmi (gut sounds) in thorax
• "Empty" abdomen on palpation
• Signs of shock: tachycardia, weak pulses, pale mucous membranes
• Vomiting, anorexia if GI organs are displaced

Radiographic Findings

• Loss of diaphragmatic silhouette (most reliable sign)
• Loss of cardiac silhouette
• Displacement of lung fields
• Gas-filled or soft tissue structures in thorax
• Absence of abdominal viscera (liver most commonly herniated)

Peritoneopericardial Diaphragmatic Hernia (PPDH)

PPDH is a congenital defect resulting from failure of the septum transversum to fuse during embryonic development. This creates direct communication between the peritoneal cavity and pericardial sac. Weimaraners and Cocker Spaniels are predisposed. Often found concurrently with other congenital defects including umbilical hernia, cryptorchidism, sternal deformities, and cardiac defects. Up to 50% of cases are incidental findings.

Clinical Signs of PPDH

May be asymptomatic (incidental finding) or present with: Exercise intolerance, tachypnea, dyspnea, cough, vomiting, anorexia, and signs of right-sided heart failure if cardiac tamponade occurs. Contents may include liver, omentum, gallbladder, stomach, or small intestine.

Treatment of Diaphragmatic Hernias

Hiatal Hernia

Hiatal hernias occur when abdominal organs (typically the stomach) protrude through the esophageal hiatus of the diaphragm into the thoracic cavity. These hernias are associated with gastroesophageal reflux disease (GERD) and are strongly associated with brachycephalic obstructive airway syndrome (BOAS).

Classification of Hiatal Hernias

Etiology and Breed Predispositions

Strongly associated with brachycephalic breeds due to increased negative intrathoracic pressure from upper airway obstruction. Breeds at risk: Chinese Shar-Pei (congenital predisposition), English Bulldogs, French Bulldogs, Pugs, and other brachycephalic breeds. May also occur secondary to trauma or as complication of diaphragmatic hernia repair.

Clinical Signs

• Regurgitation (often intermittent, especially post-prandial or with exercise)
• Vomiting and hypersalivation
• Dysphagia and hematemesis
• Weight loss and poor body condition
• Respiratory distress (especially if large hernia compresses lungs)
• Aspiration pneumonia (secondary to chronic regurgitation)

Diagnosis

Positive contrast videofluoroscopy (barium swallow) is the gold standard - shows gastric cardia crossing diaphragm into thorax. However, false negatives occur because of intermittent nature. Plain radiographs may show gas-filled viscus overlying diaphragm. Esophagoscopy reveals esophagitis and abnormal GE junction position.

Treatment

Medical management: Prokinetics (metoclopramide, cisapride), H2 blockers or PPIs (omeprazole, famotidine), sucralfate, feeding from elevated position, small frequent meals. Address concurrent BOAS.

Surgical management: For cases refractory to medical management. Combination of hiatal plication (phrenoplasty), esophagopexy, and left-sided gastropexy. Can be performed laparoscopically. Clinical improvement in 80% of cases, but complete resolution not always achieved.

Emergency vs. Elective Hernia Repair

Key Points Summary

• Umbilical hernias: Most common; congenital; small ones may close by 4 months; excellent prognosis with surgery
• Inguinal hernias: More common in females; check for bilateral; OHE/castration with repair; can trap uterus/bladder
• Perineal hernias: Intact older males; internal obturator flap technique; ALWAYS castrate; bladder retroflexion is emergency
• Diaphragmatic hernias: Traumatic (HBC) or congenital (PPDH); stabilize before surgery; liver most common organ herniated
• Hiatal hernias: Brachycephalic breeds, Shar-Pei; sliding type most common; GERD; may need BOAS correction