David Michael Tillson Department of Clinical Sciences, Auburn University, Auburn, AL, USA Hernias are defined as an opening in the body wall that permits the protrusion or movement of organ(s) or tissues out of the body cavity. Hernias are typically designated by anatomic location (e.g., umbilical hernia). Hernias can be congenital, traumatic, or surgical.1 Congenital hernias are natural openings that are present at birth. Congenital hernias can have herniated tissues in the hernia when discovered or may represent a potential opening that may develop at a future date. Traumatic hernias occur when otherwise normal tissues are torn, ripped, or ruptured, creating a defect. While most traumatic hernias occur in previously normal tissues, it is possible for traumatic events to increase the size of congenital hernias, thereby, creating a traumatic hernia in a congenital location (e.g., traumatic rupture of an inguinal ring with intestinal herniation). Surgical hernias occur after technically poor incisional closure, incomplete incisional closure, or traumatic injury that reopens a perilously secured incisional closure. This chapter will focus on three commonly encountered abdominal hernias: the umbilical hernia, the inguinal hernia, and the diaphragmatic hernia. Hernias can have three components: the hernia sac, the hernia ring, and the contents within the sac. A hernia sac is seen primarily with congenital or “true” hernias that have a peritoneal lining, such as umbilical, inguinal, and peritoneopericardial diaphragmatic hernias.1,2 Traumatic hernias, such as pleuro‐peritoneal diaphragmatic hernias or body wall ruptures, have no peritoneal lining and are called “false” hernias. As such, they have no real hernia sac, and the hernia ring tissue surrounding the protrusion is initially regular as opposed to a fibrous band in the congenital type. Hernias are further classified as being “reducible” (i.e., the hernia contents can easily spontaneously return or be manipulated into the abdominal cavity) or “non‐reducible” (i.e., the contents are not able to be replaced within the abdominal cavity). Non‐reducible hernias are additionally divided into “incarcerated” and “strangulated” hernias. Incarcerated hernias have their contents trapped in the herniated location, but the contents are typically uncompromised. Strangulated hernias have the contents entrapped as well, but these hernias also have a compromised vascular supply, resulting in the questionable vitality of the herniated tissues. Incarcerated hernias can become strangulated over time due to constriction of the hernia borders around the herniated tissues, which may eventually lead to edema, vascular congestion, and/or mispositioning of the entrapped tissues within the hernia. This means incarcerated hernias must be closely monitored until definitive repair. Conversely, strangulated hernias are surgical emergencies, requiring appropriate management in an expedited manner. It has been stated that the principles of hernia repair involve four steps.1 First, replace the herniated contents into their original anatomic location. The next steps include securely closing the hernia ring to prevent recurrence and removing any redundant material associated with the hernia sac. Finally, the surgeon should strive to use the patient’s own tissues to close the hernia whenever possible. Umbilical hernias are typically congenital and are associated with a failure of the umbilical ring to form the umbilical scar.1–3 This can occur because the ring is too large, because there is a failure of contraction, or because the umbilicus is abnormally formed, and the result is a defect that becomes an umbilical hernia.2 Most umbilical hernias are small and contain a small portion of falciform fat, creating a small, softly palpable mass at the site of the umbilicus.4 Larger umbilical hernias can occur, often having intestines and abdominal fat protruding through the hernia. Omphaloceles, which are large hernias with no subcutaneous layer or skin over the herniated viscera, are rare in veterinary medicine. Until herniation, the viscera are precariously kept in the abdominal cavity by only a peritoneal sac. Most are euthanized in veterinary medicine; however, if management of an omphalocele is attempted, the peritoneal sac‐enveloped viscera should be kept covered with an occlusive dressing until surgical reduction and hernia closure can be performed. The diagnosis of an umbilical hernia is made on physical examination. For neonates that are born via C‐section or are presented to a veterinarian shortly after birth, the physical evaluation should include checking for large umbilical hernias. Otherwise, the initial veterinary visit for routine vaccinations may be the first time an umbilical hernia is noted. The presence of a soft tissue mass on the ventral midline at the level of the umbilicus is diagnostic, and other diagnostic tests or imaging modalities are generally not required. It is important to document the size and the reducibility of the hernia in the medical record when first identified. The majority of umbilical hernias are small, non‐painful, non‐reducible masses filled with falciform or omental fat. While it is always wise to instruct owners to monitor an umbilical hernia for acute changes, these umbilical hernias are benign and are unlikely to ever be more than a minor imperfection. If desired, they are routinely addressed at the time of surgical neutering or during another abdominal procedure. Umbilical hernias are considered heritable in several breeds, such as the Pekinese, Basenji, Poodle, Airedale terrier, and Weimaraner.1–3 Umbilical hernias are also associated with numerous other congenital abnormalities, so the veterinarian needs to completely evaluate affected patients for other abnormalities. Large umbilical or cranial abdominal wall hernias in the Weimaraner breed should prompt thoracic films to evaluate the dog for a peritoneopericardial hernia. Given the benign nature of most umbilical hernias, no immediate intervention is required; rather, these hernias are often repaired in conjunction with surgical neutering. If the umbilical hernia is reducible, owners should be shown how to monitor the hernia, ensuring herniated structures do not become strangulated. This should be done on a daily basis. Sudden increases in the size of the hernia, localized swelling, and/or pain on gentle palpation warrant immediate re‐evaluation of the hernia. A change in a hernia from “reducible” to “non‐reducible” suggests surgical correction should be forthcoming, while a strangulated hernia is an emergent situation needing immediate surgery to correct the strangulation, replace or resect damaged tissues or organs, and close the defect. Most umbilical hernias are small and of minimal concern. They typically contain small protrusions of fat from the falciform ligament or the omentum. As such, they are at very low risk of clinically important herniations. Some umbilical hernias can be moderate to substantial in size with abdominal contents that readily herniate and then reduce spontaneously. While the smaller hernias may not necessitate repair, hernias that are easily reducible have the potential for tissues to eventually get trapped and potentially become strangulated. These hernias warrant monitoring and eventual repair. Umbilical hernias are seldom emergency procedures. After routine patient preparation, a ventral midline incision is made. If an ovariohysterectomy or other abdominal procedure is being performed, the standard incision is extended over the umbilical hernia for an additional 2–4 cm. Care is taken to not prematurely incise into the hernia sac, which reduces the risk of damaging hernia contents during the approach. This is especially important when the hernia is large and non‐reducible and is suspected to contain materials other than fat. If there is a concern, the surgeon can make their initial abdominal incision caudal to the umbilicus and use a finger to probe the hernia site to guide further incision and dissection. The hernia sac is dissected free, and the abdominal incision is continued to the level of the umbilicus. As the incision is continued cranially, the fibrous umbilical ring is removed on either side of the incision, and the incision continues as far cranially as needed. The defect created in this manner can be closed along with the rest of the ventral midline incision. Excessive skin associated with the hernia may need to be resected prior to final closure. If the umbilical hernia is being repaired independently of other abdominal procedures, an elliptical incision is made around the base of the hernia, and the incision is deepened to the level of the external rectus fascia. The tissue surrounding the hernia is carefully undermined until the hernia sac is encountered. The overlying skin and subcutaneous tissue are removed if excessive or incised, and the hernia sac is exposed (Figure 30.1). When the hernia is reducible, the hernia contents are pressed back into the abdominal cavity, the hernia sac is opened, and excessive tissue associated with the sac is removed. This should leave the hernia ring clearly exposed. The hernia is not ready for closure. Figure 30.1 (a) A large umbilical hernia in a male dog. The overlying skin of this umbilical hernia was continuously being abraded with daily activity, and there was concern that trauma could result in an open wound leading into the abdominal cavity and potential evisceration. Cranial is to the left in the image. (b) A ventral midline approach with herniated viscera reduced and the hernia sac opened. Surgical repair would entail resection of the hernia sac, debridement of the hernia ring, and primary closure of the hernia as a part of the midline closure. Cranial is at the top of the image. If the hernia contents are incarcerated or strangulated, additional dissection to permit resection of the hernia contents may be required. This typically involves a larger abdominal incision extending cranially and caudally from the umbilical hernia. These adjacent incisions allow the surgeon to palpate the hernia from the visceral side and determine the extensiveness of the adhesions and the vulnerability of the hernia contents that could be damaged during surgical manipulation. While small clumps of strangulated adipose tissue offer little concern, larger volumes of compromised tissues can release vasoactive compounds if the tissues are suddenly exposed to a returning blood supply. If the tissues are compromised, an attempt should be made to isolate the damaged tissues before releasing them from their strangulated location. Options for closure of the umbilical hernia are based on whether the hernia ring was resected and the size of the hernia defect. When the hernia ring is resected (i.e., “the edges are freshened”), the thick fibrous ring is removed until normal tissue is exposed. This should permit primary wound healing of the body wall, including where the former umbilical hernia was located (Figure 30.2). If the hernia defect is a part of a larger incision, it is sutured as a part of the ventral midline incision closure. The author recommends closing the body wall with a simple continuous pattern. Alternatively, if the defect is small, it can be closed with the surgeon’s preferred suture pattern: simple interrupted, simple continuous, cruciate mattress, or horizontal mattress sutures. A long‐lasting, absorbable suture material is appropriate when the ring has been resected. If the clinician decides to not resect the hernia ring, there is a concern that the wound healing might not be sufficient to prevent reoccurrence.5 In that situation, a non‐absorbable suture material, with whichever pattern, might reduce the potential for re‐herniation. The need to use a special hernia suture pattern, such as a vest‐over‐pants pattern, is typically not required in small animals. In the rare situation when an umbilical defect is too large to permit primary closure, other strategies may be needed.2 First, the surgeon can consider placing large, tension‐relieving, horizontal or vertical mattress sutures to counteract the tension across the suture line, allowing tension‐free, primary wound apposition. Another technique is to cover the defect with a polypropylene mesh sutured to the external sheath of the rectus abdominus muscle. Many surgeons will use omentum to cover the abdominal side of the mesh in an effort to minimize potential adhesion formation between the mesh and the abdominal viscera. A final technique for large defects is to use releasing incisions to create two bipedicle flaps from the rectus sheath, which can be advanced toward the midline for closure. Careful inspection of the flaps is needed to ensure that there is adherence of the external sheath to the underlying muscle, otherwise, this technique could create a new avenue for visceral herniation. Figure 30.2 Canine patient with an umbilical hernia. Cranial is to the left in the images. (a) An elliptical incision is made around the umbilical hernia, taking care to avoid injury to any underlying or herniated tissues. (b) Dissection is continued, and the hernia sac is identified and resected. (c) After dissection and reduction of all the herniated tissues, the ring of fibrous tissue surrounding the hernia is removed to expose the external rectus fascia and rectus muscle along the hernia edge. This allows for primary closure using either a long‐lasting absorbable or a non‐absorbable monofilament suture material. It is important that the closure be accomplished without excessive tension along the herniorrhaphy. Once body wall closure is accomplished, the subcutaneous closure is completed, and the skin is apposed as normal. No special postoperative care is required after umbilical hernia repair. Appropriate analgesics and a brief two‐week period of exercise restriction are all that is needed. It is a good idea to encourage owners to continue to check the surgical site for recurrence, although the likelihood of such should be very small. Inguinal hernias are typically congenital; however, traumatic abdominal injuries can also cause herniation of abdominal organs through an inguinal ring. Organs that have been identified in inguinal hernia contents include the urinary bladder, intestinal segments, and the uterus.2,3,6 Inguinal hernia is reported more frequently in female dogs compared with the males7,8 and is very rare in cats.6 Numerous breeds, including Basenji, Pekingese, Poodle, Basset hound, Cairn and West Highland White terriers, Cavalier King Charles spaniels, Chihuahua, Cocker spaniel, miniature Dachshund, Pomeranian, and Maltese dogs, have all been associated with inguinal hernias.2,3,9 In addition to occurring more commonly in females and in small dogs, non‐traumatic inguinal hernias seem to have a higher predilection for the left side.9 The uterus was the most commonly herniated organ in one report, with the intestines being the second most frequently herniated organ.9 It can be challenging to distinguish the normal fat in the vaginal process and inguinal fat from herniated organs or abdominal fat. Occasionally, local lymphadenopathy or inguinal abscesses may mimic herniated tissue. In one case series, several cats were presented with inguinal swelling after vehicular accidents with inguinal swellings that had to be differentiated from an inguinal hernia,10 and in another report, a dog developed an inguinal enterocutaneous fistula after intestinal adhesion at the level of the inguinal canal without apparent herniation.11 Traumatic episodes with subsequent increases in intra‐abdominal pressure can result in inguinal hernias that may include damage to the adjacent body wall. The influence of reproductive status and the role of reproductive hormones may also be a factor in acquired inguinal hernias, since these hernias most commonly occur in intact, middle‐aged female dogs during estrus or pregnancy.1,3 Herniation of a uterine horn can occur, requiring repair prior to full gestation to prevent parturition complications. In the male dog, herniation of abdominal viscera into the vaginal process can result in a scrotal hernia. This herniation needs to the differentiated from other testicular conditions, such as testicular torsion, neoplasia, or orchitis.8 Anatomically, the inguinal canal comprises internal and external inguinal rings and the passage that connects the two. The internal and external rings are also referred to as the deep and superficial inguinal rings, respectively. The inguinal rings are typically located approximately a centimeter cranial and medial to the femoral ring. In traumatic injuries involving the inguinal canal, these two structures may merge, resulting in a larger defect for potential herniation. The deep/internal inguinal ring is bordered medially by the rectus abdominis muscle, cranially by the internal abdominal oblique muscle, and laterally and caudally by the inguinal ligament. The superficial/external inguinal ring is a craniocaudal aperture within the aponeurosis of the external abdominal oblique muscle.12 The inguinal canal is the passage connecting the internal and external inguinal rings. Several structures normally run through the inguinal canal. These include the external pudendal vessels and genital nerve, which run along the caudal aspect of the inguinal canal, as well as the vaginal process, which contains fat and the round ligament in a female or the spermatic cord in the male. For this reason, a herniorrhaphy involving the inguinal canal should not close the defect entirely. Inguinal hernias are less commonly encountered compared to umbilical hernias, but they can occur together. The diagnosis of an inguinal hernia is made on physical examination. During the initial veterinary visit, there should be a careful palpation of the inguinal rings in puppies, since differentiation between inguinal fat and an inguinal hernia can be challenging. If the inguinal mass is large or painful, additional diagnostic imaging would be appropriate to determine the contents of the hernia. Radiographs can frequently identify intestines, urinary bladder, and other viscera. Ultrasound can help determine the viability of the contents by assessing the blood flow to the various structures. Advanced imaging is seldom required, but there may be utility in some clinical situations, like a traumatic inguinal hernia with concurrent injuries. Inguinal hernias are frequently bilateral – even if there is only active herniation on one side. The author prefers a ventral midline incision extending from the umbilicus to the pubic brim, allowing for bilateral inspection and closure of each inguinal ring. After the initial incision, the skin, subcutaneous tissues, and any mammary tissue are dissected free from the rectus fascia and retracted to expose the inguinal ring. A Gelpi or a ring retractor is useful for improved visualization when performing the procedure, especially if surgical assistance is not available. General anesthesia and the manipulations associated with surgical preparation may have reduced the herniated contents by the time the approach was made. Careful palpation will locate the inguinal hernia and determine the extent of hernia contents (Figure 30.3). Dissection of the inguinal hernia sac can be challenging, as there are frequent adhesions between the peritoneal lining of the hernia sac and the subcutaneous fat and surrounding fascia. Delicate dissection is needed to free the sac and prevent iatrogenic injury to the herniated tissues. During dissection, the hernia sac may inadvertently be opened. This is not a major issue unless the herniated tissues within the sac are damaged.
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Inguinal, Umbilical, and Diaphragmatic Hernias
Introduction
Umbilical Hernia
Etiology
Diagnosis
Timing of Surgical Repair
Surgical Procedure – Umbilical Herniorrhaphy
Closure
Postoperative Management
Inguinal Hernia
Etiology
Surgical Anatomy
Diagnosis
Surgical Procedure – Inguinal Herniorrhaphy
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