Incisional Hernia

Etiology

Incisional hernias can occur after any abdominal surgical procedure where the abdominal wall is incised. Incisional hernia has also been reported after traumatic abdominal wall injuries[1]. Incisional hernias develop because of the failure of the abdominal wall to close properly[2]. Despite advancements in techniques for abdominal wall closure the incisional hernia rate following laparotomy is as high 15% to 20%. Although research is ongoing for the ideal closure methods to prevent incisional hernias, and recent guidelines have been published, surgeons are still often faced with incisional hernias. Reasons for failure to close properly include: patients related factors, disease-related factors, and technical factors[3][4][5].

Patient-related factors that impair proper wound healing and affect the strength of the new tissue to support the abdominal wall increase the incidence of incisional hernia. Systemic chronic diseases like DM, renal failure, obesity, smoking, and malnutrition conditions; or systemic long term medications like steroids and immunosuppressants increase the likelihood of developing an incisional hernia. Morbid obesity is a common associated risk factor[6].

Disease-related factors including incision site, timing, and urgency of procedure, complications, and the underlying disease play an important role in the occurrence of incisional hernia. Emergency surgeries[7], midline incisions, infection[8], and acute abdominal surgeries are associated with a higher incidence of incisional hernia development. Wound infection, in particular, is a commonly associated risk factor with incisional hernia.

Technical factors related to the surgical technique or suture materials used for closure. Poor surgical technique may result in acute wound dehiscence or delayed healing failure in the form of incisional hernia[9]. When the fascial edges are not approximated side to side appropriately with using the appropriate strength and length of suture material incisional hernia is more likely to occur. Despite advancements in techniques for abdominal wall closure the incisional hernia rate following laparotomy is as high 15% to 20%[10]. Although research is ongoing for the ideal closure methods to prevent incisional hernias, and recent guidelines have been published, surgeons are still often faced with incisional hernias.

Epidemiology

Millions of abdominal surgeries are done in the USA and globally. It is estimated that wound healing problems occur in at least 20% of cases, many of which eventually result in an incisional hernia. Initially, the hernia may not be obvious but in almost all cases, it progresses and the patient may complain of a bulge. The condition can occur in individuals of all ages, both genders, and all ethnicities.

Pathophysiology

The exact pathophysiologic mechanism for development for an incisional hernia is not clearly known[11]. It is believed to be multifactorial. Associated factors like technical factors, including those relating to suturing techniques of the fascia, disease factors, and patient factors contribute to the occurrence of an incisional hernia. Intimate edge to edge fascial healing is necessary to provide the strength of fascia against the development of hernia[12]. The presence of gaps between the two healing edges that will be filled with healing scar predisposes for incisional hernia. These gaps or poor healing sites can be caused by the above risk factors in variable combinations. Chronically increased intraabdominal pressure predisposes more weak areas to develop hernias.

Non-midline incisional hernias are less common. Pathophysiologically, improper healing in more than one layer of the abdominal wall is required before hernia can fully develop. Less obvious or not well-defined hernias may develop from a weakness in one layer of the three abdominal muscles. Recognizing and treating this entity might be challenging. In addition, a ventral hernia can  predispose the patient to the classical complications of incarceration, obstruction or strangulation.

History and Physical

Incisional hernias are often noticed as a protrusion of the abdominal wall at the site of the incision from previous abdominal surgery[13]. This is typically more pronounced with increased intraabdominal pressure. Symptoms can range from no symptoms to discomfort, pain, or symptoms of complications like bowel obstruction and or strangulation. In most people, hernias limit patients' physical activities either due to the associated symptoms or as a precaution to avoid worsening. 

The physical exam involves abdominal palpation. In most of the cases, hernial content can be palpated. Occasional the edges of hernial defect can be felt and the size can be estimated. Planning for a surgical approach can be discussed with the patient on that visit. Although most cases of an incisional hernia are diagnosed with a history and physical, imaging is sometimes warranted like in early stages, obese patients, or complex cases[14]. Computed Tomography (CT) scanning focused on the abdominal wall is not only helpful to confirm the diagnosis when it is not clear but helps in planning the surgical approach and extent of repair[15].

Occasionally small incisional hernias are identified intraoperatively when the patients undergo another abdominal surgery. Incisions made at the same scar site or laparoscopic approach may show the fascial defects with occasional fat incarceration.

Evaluation

History and physical exam will allow for diagnosis of incisional hernias in the vast majority of cases. In cases of occult hernias, either small incisional hernias or hernias in obese patients, further workup with imaging is warranted. The computed tomography (CT) scan is the most commonly used method to diagnose an incisional hernia and can be useful in complex cases as well in helping plan operative management[15][16]. Ultrasound techniques have also been described for the evaluation of abdominal wall hernias (Dynamic Ultrasonography Assessment for Hernia-DASH). MRI can also be used to assess abdominal wall hernias but are less commonly used and is institution dependent.

Complete evaluation of incisional hernias includes confirming the diagnosis, sizing the defect, identifying the herniated content, and assessing the abdominal cavity to plan the surgical treatment in complex hernias. CT scan imaging is useful for obtaining these details.

Treatment / Management

Treatment strategies for an incisional hernia involve surgical repair or conservative nonoperative treatment[17]. In this section, a general review of the treatment principles will be discussed.  The decision to choose between the two options depends on a few factors like symptoms, the size of a hernia, complications and patients' preference. Small and asymptomatic hernias can be observed safely with a low risk of complication, 2.6% annually in some studies[7]. Unless contraindicated, large or symptomatic hernias should be surgically repaired to avoid complications, relieve symptoms, and improve quality of life. (B2)

Open, laparoscopic, and robotic techniques have been commonly used to repair incisional hernias and must be tailored to the patient and hernia characteristics[18].  In general, the mesh should be used to repair the majority of incisional hernias as they reduce the rate of recurrence compared to primary suture repair. Mesh provides the strength for the repair and scaffold for the healing tissue. There are different options for mesh placement. Onlay (above the fascial defect), inlay (between the fascial edges), sublay (below the fascial defect but above the posterior rectus sheet), and underlay or Intraperitoneal onlay (intraperitoneally below the fascial defect). 

Several different types of meshes are available.  Meshes are characterized as permanent vs. absorbable, and synthetic vs. biologic. Permanent synthetic meshes are commonly used[19]. Absorbable meshes are used in the contaminated or infected field. Biologic meshes can be used for the same reasons when long-standing support is needed and for other special indications.

In general, the fascial closure should be performed when the defect is 10 cm or smaller, and the closure augmented with mesh. If fascial closure cannot be achieved secondary to tension, other techniques such as component separation have been used. Details of the surgical repair are discussed in other articles.

Differential Diagnosis

• Cancer
• Cyst
• Lipoma
• Wound infection
• Rectus diastasis

Prognosis

The prognosis for patients with incisional hernias is guarded. Despite the use of mesh and minimally invasive techniques, incisional hernias have high recurrence rates. Infection, pain, and recurrence are common problems. If the patient does not eliminate the risk factors the risk of recurrence remains high. Bowel obstruction, strangulation, and incarceration are also serious complications of the incisional hernias.

Complications

The natural history of incisional hernia is progressive enlargement over a variable time period. It can be asymptomatic or produce one or a combination of symptoms as discussed above. Possible complications include:

- Incarceration. Incarceration can be chronic nonsymptomatic as in large defect hernias, or acute and likely symptomatic incarceration[20]. It can be reducible or irreducible, associated with other complications like obstruction or with no complication.  In chronically incarcerated hernias, adhesions develop between the hernial content and the sac. While in acutely incarcerated hernias the small defect size the cause of the incarceration.

- Obstruction. Luminal obstruction of the bowel is an acute complication that may lead to more serious complications like strangulation or perforation[21].

- Strangulation. Incarceration or obstruction can lead to strangulation, a more serious and acute complication. Strangulation should be relieved emergently.