Hernias 1: pathophysiology of hernias and principles of hernia repair Flashcards
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
Describe the aetiology of traumatic hernias
Usually blunt trauma
- Traction / avulsion injury to abdominal wall
- Tearing of abdominal muscles close to impact
Often coexist with severe injuries to other organ systems
What are the causes of incisional hernias?
Dehiscence of a surgical abdominal wound due to:
- Excessive force on incision
- Obesity
- Abdominal effusion / ascites
- Activity / coughing / straining
- Poor holding strength of wound: incorrect suture / knot technique
- Delayed healing due to infection, medication etc
List the clinical signs of an incisional hernia
- Wound inflammation / oedema
- Swelling over / around wound
- Evisceration
- Usually in acute hernias
What are congenital peritoneopericardial diaphragmatic hernias
Form due to failure of fusion of the transverse septum resulting in midline communication between the abdomen and pericardium
What are the clinical signs of a congenital peritoneopericardial diaphragmatic hernia?
- May be asymptomatic / incidental finding
- Respiratory signs: Dyspnoea, tachypnoea, cough, wheeze
- GI signs: anorexia, polyphagia, vomiting, diarrhoea, hepatic encephalopathy
- Right heart failure due to tamponade
How do traumatic diaphragmatic hernias occur?
- Usually due to blunt trauma with glottis open
- Increased pleuroperitoneal pressure gradient causes tearing of muscle of diaphragm
- Occasionally iatrogenic due to sharp trauma
List the clinical signs of a traumatic diaphragmatic hernia
- Respiratory insufficency
- May present several weeks after trauma
- Dyspnoea and exercise intolerance most common
- Head extended / elbows abducted
- Lethargy, weight loss and difficulty lying down
- Signs associated with other injuries
Where do perineal hernias usually occur?
Herniation usually occurs between the levator ani and the external anal sphincter
Describe the predispositions for perineal hernias
- Various breeds incl. border collies, boxers, poodles, OES
- Older intact males (castration reduced recurrence)
- Weaker pelvic diaphragm in males: relaxin secreted by prostate / cysts
List the clinical signs of perineal hernias
- Unilateral / bilateral perineal swelling
- Erythema / oedema / ulceration of skin
- Faecal tenesmus / pain on defaecation
- Constipation
- Flatulence
- Faecal incontinence
- Altered tail carriage
- Bladder retroflexion and dysuria
List the indications for hernia repair
- Pain
- Inflammation
- Incarceration / strangulation
- Significant protrusion affecting animal’s quality of life
- Significant risk of hollow organ incarceration / strangulation
What are the 4 goals of hernia repair?
- Ensure entrapped contents remain viable
- Release/return of viable contents to their original location
- Obliteration of redundant sac
- Tension-free and secure closure of the defect
A direct (incision over the hernia) is the approach for surgical repair in which hernia?
Uncomplicated hernia
A ventral midline coeliotomy is the surgical approach for which hernias?
- Bilateral hernias
- Internal abdominal hernias
- Traumatic hernias
- Strangulated hernias
List the possible complications of hernia repair during surgery
- Anaesthetic complications
- Haemorrhage
- Contamination
- Inability to close defect
- Loss of domain
- Poor tissue strength around repair
List the possible complications of hernia repair post-operatively
- Seroma / haematoma
- Dermatitis
- Infection
- Dehiscence / evisceration
- Pain
- Sinus tracts / enterocutaneous fistulae
- Recurrence
How can problems linked to surgical repair of hernias be prevented?
- Prepare / stabilise patient, resolve predisposing factors
- Understand anatomy and possible complications
- Correct technique / use of tissues for closure
- Control patient
- Recognise / treat complications
- Eliminate factors putting pressure on repair
