Clinical features, diagnosis, and prevention of incisional hernias

INTRODUCTION — The clinical features, diagnosis, and prevention of incisional hernias will be discussed here. The management of incisional hernias is discussed separately. (See "Management of ventral hernias" and "Laparoscopic ventral hernia repair".)

Other types of abdominal wall hernias are described in another topic. (See "Overview of abdominal wall hernias in adults".)

EPIDEMIOLOGY AND RISK FACTORS — Incisional hernia occurs in approximately 10 to 15 percent of patients with a prior abdominal incision [1]. It can develop after any type of incision, including midline, paramedian, subcostal, McBurney, Pfannenstiel, and flank incisions. The incidence depends upon the location and size of the incisions [2,3]:

●Midline incisions have the highest incidences of incisional hernias (3 to 20 percent) [4,5]. In a systematic review, the risk of incisional hernia was higher for midline incisions than transverse incisions (relative risk [RR] 1.77, 95% CI 1.09-2.87) and paramedian incisions (RR 3.41, 95% CI 1.02-11.45), respectively [6]. (See "Incisions for open abdominal surgery".)

●Vertical incisions have a higher risk for hernia than transverse/oblique incisions, and upper abdominal incisions are more susceptible to hernia than lower abdominal incisions [6-10].

●Flank incisional hernia typically develops following open surgeries involving a retroperitoneal approach, such as nephrectomy, adrenalectomy, abdominal aortic aneurysm repair, or hepatic resection. Flank incisional hernias are discussed in detail in another topic. (See "Overview of abdominal wall hernias in adults", section on 'Lumbar hernia'.)

●Incisional hernias can also develop at some laparoscopic trocar sites. (See "Abdominal access techniques used in laparoscopic surgery", section on 'Access locations'.)

Risk factors — Incisional hernias result from a breakdown of the fascial closure. The mechanism for development of an incisional hernia is multifactorial, with contributions from both patient and technical factors [11]:

Patient factors — Comorbid conditions, including old age, obesity, smoking, malnutrition, immunosuppressive therapy, and connective tissue disorders, among others, can impede normal wound healing and increase the risk for incisional hernia [12,13]. (See "Risk factors for impaired wound healing and wound complications".)

Obesity is arguably the most important patient factor that predisposes to incisional hernia formation. Obesity has been associated with increased risks of incisional hernia formation and incarceration as well as complications and recurrences following hernia repair [14,15]. In most hernia studies, the average patient had a body mass index of 33 kg/m², or class I obesity according to the World Health Organization [16,17]. (See "Preanesthesia medical evaluation of the patient with obesity", section on 'Classification of obesity'.)

Technical factors — Factors related to the abdominal surgery can also predispose to incisional hernia formation. The development of incisional hernia early in the postoperative course suggests that one or more of such technical factors (eg, infection, tension, technique) are responsible for hernia formation.

●Wound infection – Wound infection interferes with the normal wound healing process. Among patients with a surgical site infection, up to 25 percent will develop an incisional hernia; the incidence is even higher following infection in a midline incision [4,18]. (See "Complications of abdominal surgical incisions", section on 'Surgical site infection' and "Overview of the evaluation and management of surgical site infection".)

●Suboptimal fascial closure also contributes to the development of incisional hernia. As examples, excess wound tension and not achieving a suture to wound length ratio of >4:1 have both been associated with incisional hernia formation. Proper techniques of abdominal wound closure are discussed in another topic. (See "Principles of abdominal wall closure".)

●Abdominal fascial dehiscence, which may be related to broken sutures or loss of integrity of the abdominal fascia, leads to incisional hernia if not corrected. Risk factors for the development of wound dehiscence include age >70 years, male sex, chronic pulmonary disease, ascites, jaundice, anemia, emergency surgery, coughing, type of surgery, and wound infection [19]. (See "Complications of abdominal surgical incisions", section on 'Fascial dehiscence'.)

●Type of abdominal surgery – Certain types of abdominal surgery (eg, open abdominal aortic aneurysm repair or open bariatric surgery) have been identified as risk factors for incisional hernia formation [13].

Hernia risk predicting models — Models that can predict individual patients' risk of developing incision hernia have been constructed using data from large retrospective studies.

As an example, in one retrospective study of close to 30,000 abdominal surgeries, the incidence of incisional hernia requiring operative repair was 3.8 percent at close to five-year follow-up [20]. Incisional hernias occurred most frequently after colorectal (7.7 percent) and vascular surgery (5.2 percent), while prior abdominal surgery (87.5 percent) and smoking (75 percent) were the strongest patient predictors. Predictive models were constructed for eight specific operations (colorectal, bariatric, gastrectomy, gynecologic, hepatobiliary, transplant, urology, vascular) and can be used to calculate individual patient risk using an app (Penn Hernia Calc app).

DEFINITION AND CLASSIFICATION — An incisional hernia is defined as "any abdominal wall gap with or without a bulge in the area of a postoperative scar perceptible or palpable by clinical examination or imaging" [21]. Incisional hernias can be classified by anatomical or clinical criteria.

Anatomical classification — The most critical anatomical information about an incisional hernia is its location on the abdominal wall and its size.

The European Hernia Society (EHS) classification for incisional abdominal wall hernias divides the abdomen into a medial zone and a lateral zone. The medial zone, defined as medial to the lateral margin of the rectus sheath, is subdivided into five subzones (subxiphoid, epigastric, umbilical, infraumbilical, and suprapubic). The lateral zone is subdivided into four subzones (subcostal, flank, iliac, and lumbar) (figure 1). As an indication of its size, the width of a hernia is classified into three categories of <4 cm, 4 to 10 cm, and >10 cm [22]. Hernias with a defect width >10 cm are designated by some experts as complex or "giant" ventral hernias, which deserve additional scrutiny (eg, imaging) and preparation before operative repair [23]. (See 'Diagnostic evaluation' below.)

Adopting a unified classification permits direct comparison of studies on the treatment and outcomes of incisional hernia repair.

Clinical classification — Based on the clinical presentation, incisional hernias can be asymptomatic, reducible, incarcerated, or strangulated.

An incarcerated hernia is one in which the content has become irreducible due to a narrow opening in the abdominal wall fascial defect or adhesions between the content and hernia sac [24]. An incarcerated hernia containing a loop of intestine may cause bowel obstruction [25]. A population study of over 23,000 patients undergoing nonoperative management of an incisional hernia reported a cumulative incarceration rate of 1.24 percent at one year and 2.59 percent at five years [26]. Although rare, incarcerated incisional hernia can be associated with a high all-cause mortality (7.2, 10, and 14 percent at 30, 90, and 365 days, respectively).

Strangulation of a hernia occurs when the blood supply to the contents of the hernia (eg, omentum, bowel) is compromised [24]. Early intervention is crucial as delayed diagnosis or treatment can result in the need for bowel resection, which significantly increases the risk of the repair.

CLINICAL FEATURES — Incisional hernias typically develop in the early postoperative period but can present as late as 10 years after surgery; delayed presentations may be due to expansion of one or more previously undetected small hernias.

History — Patients with an incisional hernia typically complain of a bulge in the abdominal wall at the site of a prior incision. The bulge may cause varying degrees of discomfort and/or be a cosmetic concern only. Symptoms are usually aggravated by coughing or straining, with which the hernia contents protrude through the abdominal wall defect (figure 2). Large (>10 cm in width) or complex (loss of domain) abdominal wall defects can be associated with other problems such as chronic back pain, respiratory compromise, and altered body image.

Examination — On physical examination, patients usually present with a protrusion of the abdominal wall at the site of a previous incision. This is typically more pronounced with abdominal exertion or straining. In thin patients, the hernia is usually easy to identify, and the edges of the fascial defect can often be palpated. The abdominal wall should be carefully examined along the length of all incisions since multiple adjacent hernias separated by narrow bands of intact fascia ("swiss cheese"-type hernia) can be present. Large or complex incisional hernias can contain a significant amount of small or large bowel outside of the abdominal cavity, which is called loss of domain (image 1). The skin overlying large incisional hernias may show erythema, ischemia, or ulceration.

DIAGNOSIS — An incisional hernia can be diagnosed clinically in most patients without obesity. An incisional hernia should be suspected in a patient with a history of prior abdominal surgery who presents with abdominal pain or discomfort associated with an abdominal bulge. The diagnosis can be confirmed by palpation of a bulge at or near the site of a previous abdominal incision and a discrete fascial defect upon the patient relaxing the abdominal wall musculature.

Diagnostic evaluation — Patients with a suspected incisional hernia that cannot be confirmed on physical examination should undergo computed tomography (CT) of the abdomen and/or pelvis to confirm the presence of a hernia and identify any contents that might be contained within the hernia sac. Contrast is usually not necessary for the CT scan. Ultrasound has also been described for evaluation of abdominal wall hernias (Dynamic Ultrasonography Assessment for Hernia [DASH]) [27] but is more operator dependent and less widely available than CT for evaluating hernias.

CT imaging — Preoperative CT imaging is recommended for complex ventral hernias defined by a large size (>10 cm in width) and/or significant loss of domain (>20 to 30 percent of the viscera residing outside the abdominal cavity in the hernia sac) [23]. Repair of such hernias often requires advanced abdominal wall reconstructive techniques such as component separation, and patients are at a higher risk of developing major complications such as abdominal compartment syndrome postoperatively when a significant portion of the viscera is returned to the limited space of the abdominal cavity.

Preoperative CT scan can define hernia morphology, contents, the quality of abdominal musculature, and any associated conditions that could complicate the repair (eg, fistula). By knowing the precise location and size of the hernia, surgeons can better assess the potential scale of the repair operation (eg, simple repair versus component separation) and decide whether to refer to a center of excellence specializing in abdominal wall reconstruction [23]. (See "Overview of component separation".)

The radiographic relationship between the hernia sac volume and the residual abdominopelvic cavity volume is a good indication of the degree of loss of domain. The volume of the hernia sac and abdominopelvic cavity can be estimated on CT scan by multiplying the length, width, and depth of each space by a factor (eg, 0.52) to estimate ellipsoid volume [23].

The degree of loss of domain has been calculated differently by different authors. When calculated as the ratio of hernia sac volume to residual abdominopelvic cavity volume, 0.25 was the threshold above which preoperative abdominal expansion is required [28]. When calculated as the ratio of hernia sac volume to the entire peritoneal volume (ie, the sum of the hernia sac volume and the residual abdominopelvic cavity volume), a threshold >0.2 predicts difficulty with closure [29]. Sustained hypertension in the abdominopelvic cavity due to hernia reduction, visceral edema, and postoperative fluid resuscitation may lead to serious complications such as abdominal compartment syndrome. (See "Abdominal compartment syndrome in adults".)

Differential diagnosis — When discrete, separated edges of a fascial defect can be palpated or seen on imaging studies, an incisional hernia is rarely confused with other entities. However, for patients who present with abdominal pain and discomfort, it is important to ascertain whether the symptoms are caused by the hernia or another intra-abdominal pathology. (See "Causes of abdominal pain in adults".)

Occasionally, patients present with an abdominal bulge but no discrete fascial defect is palpated. In such patients, it is important to exclude alternative abdominal pathologies such as:

●Rectus abdominis diastasis (RAD) describes a condition in which an abnormally wide distance separates the two rectus muscles. When a patient with RAD raises their head and begins to sit up, the increase in intra-abdominal pressure as the two rectus muscles contract can result in a diffuse fusiform bulge, often with a protrusion of abdominal contents into the thinned, bulged midline fascia, which can be seen as a prominent ridge extending from the xiphoid to the umbilicus. However, there is no fascial defect and, therefore, no hernia. Ventral hernia can coexist with RAD, particularly if there has been a previous laparotomy. Patients with acquired RAD typically have one of two profiles: middle-aged and older men with central obesity or small, fit women who have carried a large fetus or twins to term. (See "Rectus abdominis diastasis".)

●Rectus sheath hematoma (RSH) is a rare clinical entity that results from accumulation of blood within the rectus sheath. RSH most often presents acutely with abdominal pain and a palpable abdominal mass. Due to the pattern of arterial blood supply to the rectus muscles, most RSHs occur in the lower abdomen. RSH can be distinguished from ventral hernia by CT imaging and by the lack of a palpable fascial gap. (See "Spontaneous retroperitoneal hematoma and rectus sheath hematoma".)

●Rarely, tumor involvement of the abdominal wall (eg, desmoid tumor, abdominal wall sarcoma, or metastatic cancer) can present as an abdominal bulge. However, such tumors are solid, nonreducible, and without any associated fascial gap. They are also readily discernable by CT imaging. (See "Overview of abdominal wall hernias in adults", section on 'Differential diagnosis'.)

PREVENTION — Given the high incidences of incisional hernia following open abdominal surgery, surgeons should be aware of several principles when performing a laparotomy:

Choosing an off-midline incision when appropriate — There is evidence that compared with midline incisions, off-midline incisions are associated with fewer incisional hernias. Therefore, when clinically appropriate, surgeons should choose an off-midline incision. Nevertheless, a midline incision is required in certain clinical scenarios (eg, trauma, oncology) because of the exposure that it affords. (See "Incisions for open abdominal surgery".)

Closing abdominal incisions properly — Although it is widely practiced, the technique of abdominal wound closure is not standardized. For midline wounds, we recommend a continuous suturing technique using slowly absorbable monofilament sutures at a suture to wound length ratio of >4:1. The fascia should be reapproximated en masse with low tension to prevent ischemia. In Europe, a further reduction in suture width (commonly referred to as "travel") from 10 mm to 5 to 8 mm is advocated by the 2015 European Hernia Society guidelines on the closure of abdominal wall incisions [30]. The techniques of closing midline and other abdominal incisions are discussed in detail in another topic. (See "Principles of abdominal wall closure".)

Prophylactic mesh placement — There is increasing interest in the role of prophylactic mesh at the time of abdominal closure to prevent ventral incisional hernias from occurring. However, placing mesh to repair a hernia and placing mesh prophylactically to prevent a hernia are inherently different, with the former generally accepted and the latter much more controversial.

Although prophylactic mesh placement may reduce the short-term risk of ventral incisional hernia formation, longer-term data suggest that complications may outweigh the short-term benefits. Thus, we suggest against routine prophylactic mesh placement for most patients undergoing laparotomy. However, some surgeons may choose to use prophylactic mesh in selected patients, such as those with one or more known risk factors for ventral incisional hernia. (See 'Patient factors' above.)

Prophylactic mesh placement is discussed elsewhere in a dedicated topic. (See "Prophylactic mesh for ventral incisional hernia prevention".)

MANAGEMENT — Incisional hernias can be managed expectantly or operatively, depending on the acuity of presentation and severity of symptoms. Incisional hernia repairs can be performed open or laparoscopically with techniques selected based on the location of the hernia:

●Anterior (mostly midline) incisional hernias are managed as other ventral hernias (ie, primary ventral hernias). (See "Management of ventral hernias" and "Laparoscopic ventral hernia repair".)

●Flank incisional hernias are managed as other flank or lumbar hernias. (See "Overview of abdominal wall hernias in adults", section on 'Lumbar hernia'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Ventral hernia".)

SUMMARY AND RECOMMENDATIONS

●Incidences and risk factors – Incisional hernias occur in approximately 10 to 15 percent of patients after any type of abdominal wall incision. The risk is highest after midline incisions (3 to 20 percent). Risk factors include any conditions that could adversely impact wound healing, including surgical site infection, obesity, smoking, malnutrition, and poor surgical technique. (See 'Epidemiology and risk factors' above.)

●Clinical features – Incisional hernias typically present as an abdominal bulge at or near a previous incision. In patients without obesity, the separated edges of the fascial defect can often be palpated, which is diagnostic. (See 'Clinical features' above.)

●Diagnosis – For patients with a suspected incisional hernia that cannot be confirmed on physical examination, we perform CT of the abdomen and/or pelvis to confirm the presence of a hernia and identify any contents that might be contained within the hernia sac. (See 'Diagnosis' above.)

We perform preoperative CT imaging for complex ventral hernias defined by a large size (>10 cm in width) and/or significant loss of domain (>20 to 30 percent of the viscera outside of the abdominal cavity in the hernia sac). Patients with significant loss of domain may require preoperative abdominal expansion to reduce the risk of postoperative abdominal compartment syndrome. (See 'Diagnostic evaluation' above.)

●Prevention – To reduce the risk of incisional hernia, surgeons should consider an off-midline incision when clinically appropriate and use proper fascia-closing techniques. Placing mesh prophylactically at the time of abdominal incision closure is investigational; we suggest against its routine use at the present time. Although it has some short-term benefits, the prevalence of long-term mesh-related complications is not yet known. (See 'Prevention' above.)

●Management – The management of incisional hernias can be expectant or operative, which is discussed in other topics. (See "Management of ventral hernias" and "Laparoscopic ventral hernia repair" and "Overview of abdominal wall hernias in adults", section on 'Lumbar hernia'.)