Abdominal wall reconstruction and hernias Flashcards
Describe the components of a hernia
What is the difference between a true and false hernia?
True hernia is within a normal aperture in the abdominal wall (often congenital), false hernia is in another area (often traumatic)
Are traumatic or congenital hernias more likely to be covered in a peritoneal hernial sac?
Congenital, although traumatic hernias may form a peritoneal sac over time (peritonealization). The absence of a sac in traumatic hernias places them at risk of adhesions
What is an autopenetrating hernia?
A hernia caused by a fractured rib penetrating the abdominal musculature
Describe the anatomy of the abdominal wall, specifically the levels of the fascial attachments to the linea alba as they relate to the rectus abdominis muscle.
What is the arcuate line?
The cranial most aspect where the aponeurosis of the internal abdominal oblique and transverse abdominal muscles first transition to a superficial location
What are the origins of the external abdominal oblique, internal abdominal oblique and transverse abdominal oblique muscles?
- external abdominal oblique muscles: originate from the fourth or fifth to the twelfth rib and from the last rib and thoracodorsal fascia and extend in a caudoventral direction
- internal abdominal oblique muscle: arise from the thoracolumbar fascia caudal to the last rib and from the tuber coxae. These fibers extend cranioventrally.
- transverse abdominal muscle comes from two parts: the lumbar portion arises from the transverse processes of the lumbar vertebrae and the thoracolumbar fascia, and the costal portion arises from the medial sides of the twelfth and thirteenth ribs and from the eighth to eleventh costal cartilages. Fibers from this muscle extend in a dorsoventral direction.
Label the following diagram of the location of common abdominal hernias.
What are some potential life threatening sequelae associated with abdominal herniation?
Loss of domain, incarceration and strangulation.
What are the sequelae of forcing abdominal hernia contents back into the abdomen in instances of loss of domain?
Acute pulmonary complications, poor organ perfusion (abdominal compartment syndrome).
Progressive pneumoperitoneum, inflatable silastic expanders, and the use of mesh have all been described in humans to combat loss of domain.
What is strangulation and what can cause it?
Strangulation is the devitalization of incarcerated hernial contents due to arrested circulation.
Can occur secondary to constriction of blood supply at the hernia ring, or torsion of the vascular pedicle.
What are the sequelae of strangulated viscera?
Significant blood, protein and fluid loss. Rupture will cause toxemia and septicemia. Systemic effects may be greater for hernias surrounded by peritoneum as this will allow more rapid uptake of vasoactive substances.
What are the main goals of hernia repair?
- Ensure the viability of the entrapped hernia contents.
- Release and return viable hernia contents into their normal location.
- Obliterate redundant hernial sac tissue.
- Provide a tension free and secure primary closure.
When are autologous muscle or fascial flap development preferred over prosthetic implants (such as polypropylene mesh) for hernia closure?
In an infected environment/presence of gross contamination.
What are the three indications for surgical repair of an abdominal hernia?
- Hernia is symptomatic
- Large protrusion that affects quality of life
- Risk of strangulation
The falciform ligament is the remnant of which embryonic structure?
The umbilical vein (the middle umbilical ligament of the bladder is the remnant of the urachus)
Are umbilical hernias considered inherited?
Yes, affected animals should not be bred
What other congenital abnormalities have been reported with umbilical herniation?
Failure of caudal sternal fusion, cranioventral abdominal hernias, cryptorchidism, concomitant diaphragmatic hernias.
Any patient presenting with an umbilical hernia should be thoroughly investigated for other congenital abnormalities.
Which breeds of dogs are predisposed to umbilical herniation?
Airedale terriers, Basenjis, Pekingese, Pointers and Weimaraners
Is there a sex predilection for umbilical herniation?
Not for the general population. Females overrepresented amongst at risk breeds
What is an omphalocele?
Large midline umbilical and skin defect that permits abdominal organs to protrude from the body. Usually covered by a transparent membrane of amniotic tissue.
Is conservative management reasonable in a puppy with a small asymptomatic (<2-3mm) umbilical hernia?
Yes, may spontaneously regress by 6 months of age
What are some techniques that can be used in instances of large abdominal wall defects with umbilical hernia repair?
Fascial release incisions, component separation technique, prosthetic materials.
Describe the difference between a direct and indirect inguinal hernia?
Indirect hernias enter the cavity of the vaginal process, whereas direct hernias pass through the inguinal rings adjacent to the vaginal process.
Are direct or indirect inguinal hernias more likely to result in strangulation?
Indirect, because the vaginal process is narrow at the inelastic inguinal ring.
Are congenital inguinal hernias more likely in male or female dogs?
Male, possibly due to delayed inguinal ring narrowing and late testicular descent.
Acquired inguinal hernias are most frequently seen in which patients?
Middle-aged, intact bitches
What are the vessels that pass through the caudomedial aspect of the inguinal canal?
External pudendal vessels, genital branch of the genitofemoral nerve, artery and vein
What are the anatomic boundaries of the internal and external inguinal rings?
Which breeds of dog have a proven inheritable influence for inguinal hernia development?
Golden retrievers, Cocker spaniels and Dachshunds
What are the factors potentially involved in inguinal hernia formation?
Anatomic: increased size of vaginal process, short wide inguinal canal in bitches.
Hormonal: Estrogen thought to play a role
Metabolic: obesity may increase abdominal pressure and fat may dilate the vaginal process
What concurrent condition are male dogs with inguinal hernia at increased risk for?
Cryptorchidism, an association between inguinal and perineal hernias has also been described.
On which side are inguinal hernias more likely to occur?
Left
Is strangulation of hernia contents more common in male or female dogs?
Male
What are some clinical signs that might suggest strangulated intestine in an inguinal hernia?
Vomiting, abdominal pain, depression
What are some DDx for scrotal hernias?
Testicular torsion, testicular or scrotal abscess, neoplasia, orchitis, hydrocele
Why do you need to leave a gap caudally when performing inguinal hernia repair?
To allow unconstrained passage of the external pudendal and genitofemoral vessels, genitofemoral nerve, and spermatic cord (in intact dogs).
What muscle flap could potentially be used to augment large inguinal hernia defects?
Sartorius. This can be combined with prosthetic mesh if required.
Up to what stage of gestation may an incarcerated gravid uterus in an inguinal hernia potentially be salvaged?
7 weeks
What are the most common complications after inguinal hernia repair?
Seroma and hematoma. If castration is not performed swelling of the scrotum may occur in instances of lymphatic and venous drainage occlusion - may require surgical revision.
True or false? An increased incidence of testicular tumours in dogs has been associated with scrotal hernias?
True. Castration is recommended with scrotal hernia repair for this reason and to prevent production of offspring.
In a strangulated inguinal hernia is the surgical approach abdominal or extraabdominal?
Should be abdominal to ligate and transect structures entering the inguinal ring, this allows for en bloc resection of the hernial sac (+/- scrotal ablation) and removal of macerated tissues.
When castration is not performed at the time of scrotal hernia repair, how is recurrent hernia formation prevented?
Partial ligation of the parietal vaginal tunic
What is the prognosis for inguinal hernia repair?
Good to excellent if uncomplicated (3% mortality rate).
Describe the anatomy of the femoral canal
Femoral herniation typically occurs caudomedial to the femoral vessels and lateral to the inguinal ligament through a potential space known as the femoral canal.
What are the most common causes of femoral herniation?
Iatrogenic damage to the pectineus or blunt trauma (can result in a large defect from avulsion of both the pubic and inguinal ligaments)
How is closure of an uncomplicated femoral hernia achieved?
Suturing of the pectineus muscle to the inguinal ligament. If contents are incarcerated or strangulated may require a concurrent ventral abdominal approach.
What should be placed post-operatively in the case of a tenuous femoral hernia repair?
Hobbles
If significant distal limb swelling is observed following femoral hernia repair, what could be the cause?
Obstruction of the lymphatic or venous drainage at the femoral canal. Re-exploration is indicated (or if a femoral nerve deficit is present post-op).
What are the most common areas of herniation following blunt trauma?
Ventrolateral abdomen (inguinal, prepubic regions) and paracostal regions. Dorsolateral and paracostal hernias might be more common in cats.
A sudden increase in intraabdominal pressure following blunt trauma commonly results in injuries to which area of the abdominal wall?
The paracostal area (between the origins of the tranverse and external abdominal oblique muscles).
What are common body wall hernias that result from avulsion forces (contracted abdominal muscles and open glottis limiting increases in intrabdominal pressure)?
Prepubic, inguinal and dorsolateral (muscle avulsion from the transverse processes of the lumbar vertebrae)
What injury is commonly found in conjunction with paracostal herniation?
Diaphragmatic herniation
What percentage of patients with abdominal hernias have other significant injuries?
75%
What are the most definitive radiographic signs of abdominal herniation?
Loss of abdominal strip, absence of an organ from its normal location, organ displacement into the subcutaneous tissues.
Ultrasound, CT, MRI may be beneficial in difficult to diagnose cases.
What is the ideal time of repair of acute traumatic herniation?
Controversial - delay of a few days if non-urgent may improve the quality of tissue for closure (reduced edema, improved blood supply), excessive delay may result in contraction and strangulation or increased adhesions.
Are acute or chronic abdominal body wall hernias best approached directly over the hernia or via a ventral midline approach?
Acute: often best approached through ventral midline. Allows assessment of abdominal organs and often more easily repaired intra-abdominally.
Chronic: can be repaired via direct incision over the defect (so long as no strangulation of content)
Why are vascularized tissue flaps preferred over the use of prosthetic mesh in hernia repair where possible?
Can survive in an infected or highly contaminated environment
Describe a decision making tree for abdominal hernia repair.
How are prepubic tendon ruptures repaired?
Suture placed through holes in the cranial pubic ligament and then through holes in the pelvis (modified dorsal recumbency position useful to reduce tension on the closure). A rectus abdominus muscle flap has also been described.
What can be used to augment repair of a prepubic ligament rupture when shredded or avulsed?
Mesh cuff or double layer mesh technique.
How are paracostal hernias repaired when there is limited soft tissue attachments remaining to bone?
By passing sutures through bone tunnels, or bone anchors or around ribs. If there is adequate soft tissue the transverse abdominal, internal and external abdominal oblique muscles are repaired primarily via an intraabdominal approach.
What are some potential causes of incisional herniation?
Technical causes are the most common!
Otherwise excessive forces on the incision (increased intra-abdominal pressure), or poor holding strength of the wound (incorporating fat in sutures, inappropriate material/size, infection, inappropriate suture interval [should be 4:1 suture to length of the wound, i.e. 5-7 mm fascial bites, and 3-4 mm of travel])
What is an early sign of impending incisional dehiscence?
Swelling and serosanginous discharge
What are some difficulties associated with chronic incisional hernia repair?
May have loss of domain, significant fibrous tissue may make identification of the holding layers difficult. May require repair with prosthetic mesh materials.
What are some factors associated with an increased duration of hospitalization in patients with evisceration?
Evisceration secondary to trauma, high lactate on admission, small body size.
What are the advantages of autologous vs. mesh hernia repair?
Autologous: dynamic and vascular support particularly in a contaminated environment.
Mesh: simpler to perform and no donor site morbidity.
What are some autologous repair options for large body wall hernias?
Vacuum-assisted closure, separation of abdominal body wall components (fascial releasing incisions and adjacent tissue transfer [see image]), abdominal wall partitioning (a series of parasagittal staggered incisions in the fascia), muscular flaps (cranial sartorius, external abdominal oblique, rectus abdominis).
What are the limits of the cranial sartorius muscle flap?
Can cover 30% of caudal abdomen when positioned transversely along pubis, can reach 80% of length of abdomen if positioned parallel to midline. Good for prepubic, inguinal and femoral hernias.
What vascular pedicle supplies the cranial sartorius muscle flap?
A branch of the femoral artery
What defects are external abdominal oblique myofascial flaps useful for?
Ventral, cranial to mid-abdominal wall defects (10 x 10cm in size has been reported). Is an island flap reliant on the cranial branch of the cranial abdominal artery.
What vessels supply the rectus abdominis muscle flap?
The cranial and caudal superficial epigastric vessels. It is thicker than the sartorius muscle flap. Good for prepubic tendon rupture
What vessels supply the cranial sartorius muscle flap?
A branch of the femoral artery and vein in the proximal third of the muscle
What vessels supply the rectus abdominus flap?
The cranial and caudal superficial epigastric vessels. Provides additional thickness and strength compared to the cranial sartorius.
What are the typical causes of prosthetic material failure in hernia repair?
Infection or tension. Also require adequate skin and subcutaneous coverage.
Why is it ideal to interpose omentum on the peritoneal surface of a prosthetic material?
Helps to seal the defect, brings blood supply and healing cells to the area, avoids the risk for visceral adhesions
What are the main disadvantages of prosthetic implant materials in hernia repair?
Sinus formation and chronic infection
What is the most widely used synthetic mesh material?
Polypropylene (porous non-absorbable material that allows abundant growth of fibrous tissue). Composite meshes may have benefits but are yet to be studied in animals.
What are some potential advantages and disadvantages of tissue grafts over synthetic mesh materials?
Tissue grafts (SIS, dermis or pericardium) are completely resorbed and replaced by native collagenous tissues. This may increase wound strength and reduce the risk of chronic FB inflammatory responses. However, remodelling and replacement may be inconsistent and it remains to be determined whether use of tissue grafts results in strong wounds long term. Their response in infected wounds is also unknown.
What are the different mesh implantation techniques?
Overlay, underlay and interpositional
Which mesh implantation technique is preferred?
Underlay, as has the lowest rate of reherniation and wound related complications (infection, seroma, hematoma). Downside is direct contact with abdominal viscera which may result in enterocutaneous fistula formation and adhesions. This can be minimized with the use of omentum.
Why are interpositional mesh implantation techniques infrequently used?
Minimal attachment between the mesh and the adjacent fascia (strength holding layer) resulting in frequent re-herniation.
What is the disadvantage of overlay mesh techniques?
High rate of wound related complications (seroma, hematoma, extrusion, infection). Advantage is that there is minimal contact with the abdominal viscera reducing the risk of adhesion and enterocutaneous fistula formation.
What are the common complications associated with abdominal wall herniorrhaphy?
