Risk factors for hernia development Smoking, infection, obesity, chronic cough, excessive straining during bowel movements or while urinating, pregnancy, straining to lift heavy objects, and persistent sneezing, such as might accompany allergies, are clear risk factors for causing or exacerbating an existing hernia. The common basis for these risk factors, with the exception of smoking (excluding smoker's cough) is increased pressure on the abdominal wall. The link between smoking and hernia formation relates to metastatic emphysema, in which the same tobacco-induced defect in collagen formation that leads to alveolar stretching and breaking in the lung tissue also causes abnormal collagen formation in the abdominal muscles. Similarly, in patients with diverticulitis, the cause of weakness in the intestinal wall seems to carry over to a weakened abdominal wall and an increased risk of hernia. Patients with an aortic aneurysm may also have a biochemical or structural predisposition to hernia due to an underlying collagen defect. Other risk factors for hernia formation include cirrhosis with abdominal ascites and other debilitating disorders that cause decreased tissue strength and muscle mass.

Smoking cessation and weight reduction in overweight or obese patients are 2 strategies for reducing the risk of hernia. In patients with a known predisposition to hernia formation, avoiding heavy lifting or straining might lessen the chances of hernia formation. Improving muscle tone through aerobic exercise or weight lifting does not appear to be preventive; even athletes with good muscle development and strength experience hernias.

Why treat the asymptomatic hernia? A patient whose hernia causes no discomfort and reduces spontaneously is in no immediate danger. A hernia that reduced spontaneously could become incarcerated and strangulated, however, and lack of symptoms does not necessarily mean that a hernia is harmless and can be left alone. Unless a defect is very large—with a decreased risk of the herniated sac becoming trapped outside the abdominal wall—it should be surgically repaired. An abdominal wall defect which is very small, causes no lifestyle changes, and remains asymptomatic may be followed with regular observation, unless a change in status requires repair. In patients who are poor candidates for surgery, large defects should be followed regularly, and the defect should be repaired if and when the patient can be cleared for surgery. Although most hernias will be asymptomatic when detected, they require repair in a timely fashion. Delaying surgery until it becomes emergent introduces additional risk, including ischemic damage to the affected tissue before the trapped tissue can be freed, as well as the inability to stop medications such as aspirin prior to surgical intervention.

A relatively new class of hernias, called trochar site hernias, in particular requires timely diagnosis and repair. These hernias may result from laparoscopic abdominal surgeries such as cholecystectomy, hysterectomy, hernia repair, or appendectomy, when the holes made by trochars or access ports do not close properly. As the use of laparoscopy increases for many operations, the incidence of trochar site hernia is likely to increase.

Table 1: Differentiating abdominal wall hernias

Confirming the clinical diagnosis The typical presentation of an abdominal wall hernia is a visible, palpable, and identifiable bulge. Symptoms may include a sensation of fullness in the affected area and mild or moderate discomfort, especially with heavy lifting or straining. The pain might worsen as the day progresses, particularly if the patient is standing for long periods of time. Asymptomatic hernias are frequently discovered on routine physical examination, and many are not found until they become symptomatic (see Table 1). Obesity, scar tissue from a previous incision, or musculoskeletal pain can complicate the clinical diagnosis.³ Strangulation and blockage of intestinal tissue occur may cause severe pain, vomiting, fever, constipation, and shock.

In patients who are not overweight, the physician may be able to feel the defect in the abdominal wall by moving the patient from a supine to an upright position, by recreating a situation known to cause the hernia to bulge such as having the patient cough forcefully or by performing a Valsalva's maneuver. It might be more difficult to detect a hernia that has been repaired multiple times, as scar tissue could prevent the hernia from bulging sufficiently to be seen or felt.

The differential diagnosis of a potential hernia will typically include lipoma, hematoma (following trauma or surgery), lymphadenopathy, and tumor. With a tumor or lipoma, however, there is no hole to palpate and the tumor does not reduce in response to pressure.

Herniography and CT are the gold standard diagnostic tools for incisional hernias. The CT order should specifically instruct the technician to determine the presence and location of an abdominal wall hernia, the number of defects present, and the contents of the herniated sac. It is important that the technician know whether the patient has undergone a previous mesh repair.

Because abdominal wall hernias tend to bulge when the patient is upright, it would make sense to simulate that position for imaging purposes. One report demonstrated how CT can be done with patients performing a Valsalva's maneuver while in the decubitus position toincrease pressure on the abdominal wall.⁴ Ultrasound (US) imaging is a less expensive alternative to CT but one that requires a skilled technician and the patient's ability to push out the hernia.

Unusual presentations Less common abdominal wall hernias are differentiated by the sac contents.⁵ A spigelian hernia, for example, has a preperitoneal or peritoneal sac that usually contains small or large bowel but can also house the stomach, omentum, or appendix. It constitutes no more than 2% of all abdominal wall hernias, can be congenital or acquired, and tends to occur in women more than men. It may be confused with an abdominal wall lipoma.⁶ About half of all cases of spigelian hernia occur in patients with previous abdominal surgery.⁵ Typically while standing, a patient feels pain and a mass that the physician can not palpate. US is a valuable tool in detecting these hernias, which usually have a small neck size, contributing to a 20% to 30% incarceration rate on surgical presentation.⁵

Littre's hernia is an incarcerated or strangulated Meckel's diverticulum that is present in any type of abdominal wall hernia.⁵ Symptoms include middle abdominal pain, nausea, vomiting, and signs of intestinal obstruction. In Richter's hernia, the antimesenteric border wall becomes strangulated or incarcerated. Symptoms may include nausea, vomiting, localized pain—perhaps over the site of a previous incision, fever, and leukocytosis. Signs of partial bowel obstruction may also be present. Richter's hernia is more common in elderly patients who have been ill and become dehydrated.

Internal abdominal hernias are a group of rare herniations in which an abdominal organ protrudes through a normal or abnormal mesenteric or peritoneal aperture.⁷ These hernias may develop as a result of trauma or surgery or may be related to congenital peritoneal defects. Nonspecific symptoms may include mild abdominal discomfort, episodic, intense periumbilical pain, and nausea. This type of hernia is very difficult to diagnose, even on radiographic studies.

Surgical treatment options Nonsurgical approaches have proven unsuccessful in treating hernia. Belts or trusses designed to apply counterpressure to the abdomen may provide some symptomatic relief, but they do not decrease the risk of enlargement or incarceration and, if worn improperly, may actually increase the risk of incarceration.

Historically, hernia repair involved securing a defect by sewing it closed. Over time the hole typically reopened—analogous to a tear in the knee of a pair of jeans that is repaired by sewing together the torn ends of fabric, which ultimately cannot hold with repeated stress on the seam. Modern approaches to hernia repair can be compared to patching the hole in the jeans rather than stitching it closed. Advances and improved outcomes have come from experimenting with different types of patch materials and from modifications of the method used to attach the patch to the defect, for example, sewing the patch over the hole from the inside or from the outside. State-of-the-art hernia repair utilizes a mesh patch, which varies in its make-up and physical characteristics and is stitched in place using an open surgical or laparoscopic technique.

The key to achieving a recurrence rate of less than 1% is to prevent tension at the site of the repair. (Note that the rate of recurrence for incisional hernias at the site of a previous surgical procedure is greater than that for inguinal hernia, which is less than 2%.) A strong, long-lasting repair is the responsibility of the surgeon, who selects the appropriate surgical technique, the site of mesh placement, and the type of patch to use.

Comparing open and laparoscopic mesh repair of incisional hernias, one study demonstrated a higher rate of postoperative infections—14% versus 4%—with open repair.⁸ The recurrence rate at 2 years was 18% after open repair and 15% after laparoscopic repair. All the recurrences in the laparoscopic group occurred among the first several cases, in which staples were used to attach the mesh. The main advantage of laparoscopic hernia repair is the absence of a large incision and the fact that patients will typically feel better sooner. Questions remain, however, as to whether a laparoscopic repair will be as effective and last as long.

In a study comparing mesh and suture repair of incisional hernia, 181 patients with a first-time midline incisional hernia were randomly assigned to suture or mesh repair.⁹ The authors reported a 10-year cumulative rate of recurrence (based on 75 to 81 months of follow-up) of 63% for suture repair and 32% for mesh repair (P <0.001). For small incisional hernias, the recurrence rates after suture and mesh repair were 67% and 17%, respectively. In this study, patients who underwent suture repair reported more frequent abdominal pain.

Complications of hernia surgery include those of any surgical procedure, such as infection, bleeding, and fluid collection. Infection poses an additional risk in hernia surgery; depending on the type of mesh used, the mesh itself can become infected and require removal, and the hernia re-repaired. Bacteria can infiltrate the pores of nonabsorbable mesh material. Even if the mesh pores are smaller than 10 μm in size, for example, a 1-μm bacterium could penetrate the mesh. A 10-μm WBC, such as a protective macrophage, however, would not be able to enter. Other potential complications of hernia surgery include enterocutaneous fistula, intestinal obstruction, wound sinus infection, deep vein thrombosis, and pulmonary problems.¹⁰

Due to the risk of infection, it is desirable for a nonabsorbable mesh to have a pore size larger than 15 μm. For further benefit, having some pores larger than 150 μm in size would allow the patient's tissue to penetrate the mesh, helping to keep it in place and strengthening the repair. The wider the weave and the more holes in the mesh, the more easily tissue can penetrate and the lighter and more flexible the material. Ideally, the mesh should be made from a monofilament to prevent bacteria from lodging in the spaces created by braided fibers. To allow for contraction, mesh used for hernia repair should be bigger than the hole.

Advances in hernia repair surgery Ongoing advances in hernia repair surgery center on the biomaterials used to close the hole in the abdominal fascia using tension-free repair techniques. Driving these innovations is the search for an optimal mesh that combines several key qualities: strength and resistance to tearing, flexibility, resistance to infection, and a surface that will not adhere to the bowel during healing, which can lead to erosion and intestinal fistulas.

To enhance the strength of an incisional hernia repair, placing the mesh patch under the abdominal muscle, rather than on top of it, has proven effective. The mesh should be situated as deeply as possible, preferably above the peritoneal layer without being placed in the peritoneal cavity if the mesh lacks a protective layer against the bowel. A mesh inlay will better resist the intra-abdominal pressure pushing outward on the defect, and, in fact, the intra-abdominal pressure that caused the hernia to form could actually be protective.

The preferred placement of a mesh inlay is between the peritoneum and the abdominal wall muscle, behind the abdominal rectus muscle. This approach yields very low recurrence rates: 2% to 5% for large hernias and approaching 0% for small hernias. Alternatively, the mesh can be placed inside the peritoneum. One problem with this method is that the mesh will come in contact with the intestines, resulting in possible infiltration and intestinal fistula formation. Attempts to place a protective bioabsorbable layer between the mesh and the bowel have had limited success. Nonabsorbable materials have been shown to work well.

These findings led to the development of composite materials that contain a layer of mesh bound to a layer of nonabsorbable material. The material is placed so that the protective layer comes in contact with the intestine. The most commonly used materials to create this protective layer are silicone rubber, polypropylene, and polytetrafluoroethylene (PTFE).

Biosynthetic meshes have some advantages over permanent meshes. They are more resistant to infection, and, over time, they stimulate tissue growth in the area of the defect and become incorporated into the patient's tissue. A determination on their long-term effectiveness and associated recurrence rates will require ongoing evaluation.

This consensus article was written by Vicki Glaser in consultation with Drs Amid, Graham, and Selwyn.

Dr Graham discloses that he has an ongoing relationship with Ethicon.

Drs Selwyn and Amid discloses that they have no financial involvements with any companies doing business in this field.

REFERENCES 1. The American Medical Association: The causes and surgical treatment of abdominal hernia. Available at: http://www.medem.com/MedLB/article_detaillb.cfm?article_ID=ZZZESG4TWAC&sub_cat=195. Accessed March 31, 2005.

2. Rutkow IM. Demographic and socioeconomic aspects of hernia repair in the United States in 2003. Surg Clin North Am. 2003;83:1045-1051.

3. Aguirre DA, Casola G, Sirlin C. Abdominal wall hernias: MDCT findings. Am J Roentgenol. 2004;183:681-690.

4. Emby DJ, Aoun G. CT technique for suspected anterior abdominal wall hernia. Am J Roentgenol. 2003;181:431-433.

5. Montes IS, Deysine M. Spigelian and other uncommon hernia repairs. Surg Clin North Am. 2003;83:1235-1253.

6. Bell RL, Longo WE. Spigelian hernia. J Am Coll Surg. 2003;199:161.

7. Mathieu D, Luciani A; GERMAD group. Internal abdominal herniations. Am J Roentgenol. 2004;183:397-404.

8. van't RM, Vrijland WW, Lange JF, et al. Mesh repair of incisional hernia: comparison of laparoscopic and open repair. Eur J Surg. 2002;168:684-689.

9. Burger JW, Luijendijk RW, Hop WC, et al. Long-term follow-up of a randomized controlled trial of suture versus mesh repair of incisional hernia. Ann Surg. 2004;240:578-583.

10. Basoglu M, Yildirgan MI, Yilmax I, et al. Late complications of incisional hernias following prosthetic mesh repair. Acta Chir Belg. 2004;104:425-428.