Hernias 1: pathophysiology of hernias and principles of hernia repair Flashcards
(41 cards)
What is a hernia?
A full thickness defect in an anatomical structure
What is a hernia composed of?
A ring (the border of the defect)
A sac (a mesothelial layer covering any tissues that have protruded through the ring).
How can hernias be classified?
Several ways:
- Internal (defect is within the body) or externa (defect is in the body wall)
- True hernias or false hernias
- Spontaneous or acquired
- Reducible, incarcerated or strangulated
What are true vs false hernias?
True = the defect is due to enlargement of a normal opening e.g. an umbilical hernia
False = the defect is due to trauma or a disrupted surgical wound e.g. an incisional hernia
What are spontaneous vs acquired hernias?
spontaneous = mostly congenital
acquired = usually after trauma or surgery
Compare reducible vs incarcerated vs strangulated hernias
Reducible = the contents can be moved back into their original location
Incarcerated = the contents are trapped within the hernia
Strangulated = the contents are trapped and their blood supply is obstructed
Name the 3 main problems caused by hernias
Loss of domain
Incarceration
Strangulation
Describe loss of domain as a problem caused by hernias
If a substantial volume of viscera herniates, the abdominal wall adapts to the lower volume of abdominal contents and contracts, making reduction of the hernia and primary closure of the defect difficult or impossible.
When there is a loss of domain what are the consequences of closing the defect without reducing the tension in the abdominal wall?
- Increased intra-abdominal pressure (compartment syndrome)
- Reduced organ perfusion
- Reduced ventilation due to pressure on the diaphragm
- Dehiscence of the repair
Describe incarceration as a problem caused by hernias
If the ring is small and inelastic (e.g. scrotal or femoral hernias) then herniated organs can become trapped.
This can rapidly progress to strangulation so early diagnosis and repair of incarcerated hernias is essential
Describe how incarceration affects hollow organs
Obstruction of the lumen of hollow organs
e.g. the uterus (causing dystocia), small intestine (causing abdominal pain, vomiting, anorexia) or bladder (causing dysuria)
How does strangulation due to hernias occur?
- Constriction of the organ’s blood supply at the ring.
- Torsion of the blood vessels to/from the organ: this is more common in organs with long, mobile vascular pedicles e.g. uterus, intestine, testicle
What are the consequences of strangulation due to hernias?
- Venous drainage affected first, followed by arterial inflow
- Organ necrosis and potentially rupture
- Can be acute or delayed
- Release of contents may worsen condition
- In most cases the herniated tissue is devitalised by the time of surgery and must be resected
Name the most common type of hernia
Umbilical hernias
Describe the predisposition to umbilical hernias
Inherited - Airedales, basenjis, Pekingese, pointers and Weimaraner’s are at greater risk.
Females are more commonly affected
Describe the aetiology of umbilical hernias
- Due to incomplete fusion of ventral abdominal wall
- Affected animals often have other congenital defects e.g. diaphragmatic hernias
Describe the clinical signs of an umbilical hernia
- Soft, round swelling at the umbilicus which may be firm or hard if fat or viscera are entrapped.
- Entrapment of intestine may lead to intestinal obstruction and pain, vomiting and anorexia.
What is a direct inguinal hernia?
Viscera pass through the inguinal canal ALONGSIDE the vaginal process.
These hernias are usually large and most do not cause incarceration or strangulation.
What is an indirect inguinal hernia?
- Viscera pass THROUGH the inguinal canal inside the vaginal process.
- These are more common
- More often cause entrapment/strangulation because the vaginal process narrows considerably at the inguinal ring
Describe the aetiology of inguinal hernias
The inguinal rings are openings in the abdominal wall linked by the inguinal canal. Several factors may contribute to the development of inguinal hernias
- Weakening of the abdominal wall due to malnutrition or catabolic diseases may predispose to herniation.
- Obesity increases intraabdominal pressure and fat deposition may dilate the vaginal process and inguinal canal, predisposing to herniation.
- Breed, sex
Which animals are predisposed to inguinal hernias?
- Heritable predisposition in golden retrievers, cocker spaniels and dachshund
- The short length of the inguinal canal in females may make herniation more likely
Describe the clinical signs of inguinal hernias
- Unilateral or bilateral
- Soft, painless mass over the inguinal area but may be painful or hard if the contents are incarcerated or strangulated
- Large hernias may contain bladder, uterus or intestine and may extend caudally so they resemble a pendulous perineal hernia
Describe the features and signs of scrotal hernias
- Indirect inguinal hernias in male dogs
- Possibly congenital defect in inguinal ring
- Usually unilateral
- Present with pain and swelling
- Incarceration / strangulation common
Describe the features and signs of traumatic hernias
- False hernias / ruptures
- Lack a sac so more prone to adhesions / incarceration
- Can cause strangulation as ring contracts during healing
- Bulging subcutaneous mass / abdominal asymmetry
- May vary in size / shape
- Clinical signs associated with other injuries
