Abstract
An abdominal wall hernia is the abnormal protrusion of an intra-abdominal viscus, or part of a viscus, through a defect in the muscular and fascial layers of the abdominal wall. A prompt and thorough assessment must be carried out in order to differentiate hernias, particularly those containing bowel, from other causes of abdominal swelling. Abdominal wall hernias are one of the commonest types of hernia that a GP will encounter in their daily practice. This article discusses the diagnosis, differential diagnosis and management of commonly presenting abdominal wall hernias.
Clinical case scenario
You are asked to review a previously independent 78-year-old lady who presents with a 2-day history of abdominal pain and vomiting. The daughter reports that the vomitus is very dark in colour and foul-smelling. On examination, she appears clinically dehydrated. Her abdomen has no scars, is distended and tympanic, and there is a tender, irreducible lump in her left groin. You make the diagnosis of an obstructed femoral hernia and make an urgent referral to the on-call general surgeons.
Definition
The term ‘hernia' is derived from Latin meaning ‘rupture' and denotes the protrusion of a viscus, or part of a viscus, through an abnormal opening in a wall of the cavity that normally contains it. The most common hernias to present to general practice are those of the abdominal wall. In this context, the herniating tissue is typically bowel, omentum or intra-abdominal fat, and the abnormal opening is a defect or focal weakness within the complex layering of muscle and fascia of the anterior, lateral and occasionally posterior, abdominal wall. As the herniating tissue increasingly protrudes through the defect, it takes with it the lining of the cavity (usually peritoneum), which thereafter encloses the hernia and is known as the hernia ‘sac’. The area of the hernia at the abdominal wall defect is the ‘neck’ of the hernia. The anatomy of a hernia is illustrated in Fig. 1. Abdominal wall hernias commonly presenting to general practice are illustrated in Fig. 2.
The anatomy of a hernia. The hernia sac (yellow) is derived from peritoneum, which lines the abdominal cavity and encloses the hernia as it protrudes through the musculofascial layer (blue) of the abdominal wall. The hernia neck is the portion of hernia at the level of the muscular defect and represents the hernia "pinch point". Abdominal wall hernias commonly presenting to general practice.
Epidemiology
Abdominal wall hernias are common, with an estimated prevalence of 4% in those above the age of 45 years and a lifetime risk of developing an abdominal wall hernia of 5%. Inguinal hernias are by far the most common type of hernia seen both in men and women, accounting for approximately 75% of all abdominal wall hernias, followed by paraumbilical/umbilical, epigastric, incisional and femoral. Groin hernia repairs are therefore one of the commonest performed surgical procedures, with nearly 80 000 repairs carried out in England every year and a staggering 20 000 000 groin hernia repairs carried out worldwide (Simons et al., 2018).
Aetiology of abdominal hernias
Congenital hernias are rare, present from birth and result from an abdominal wall defect that fails to close during fetal development. The most severe forms of these are associated with other chromosomal abnormalities, prematurity and low birth weight. Hence, exomphalos occurs where the bowel fails to return into the abdominal cavity during fetal gut development and herniates alongside the umbilical cord. Gastroschisis occurs when the bowel returns to the abdominal cavity following development, but the abdominal wall defect fails to close. The prenatal diagnosis of these disorders on ultrasound allows planned delivery in a tertiary neonatal centre and early surgical repair following birth. More straightforward and less severe congenital hernias are primary umbilical and epigastric hernias. More than 80% of congenital umbilical hernias will close before the age of 5 years and do not require repair unless complicated. Other hereditary disorders associated with hernias include cystic fibrosis and connective tissue disorders such as Ehlers–Danlos syndrome.
Acquired hernias are much more common in occurrence with increasing age and co-morbidity. They typically result from weakness of the abdominal wall musculature combined with a sustained or repeated rise in intra-abdominal pressure. They are more commonly seen in patients with chronic systemic diseases such as diabetes, renal failure, malnutrition, and patients taking long-term steroids or immunosuppressant medications. Other risk factors include smoking, morbid obesity, chronic obstructive airways disease and chronic straining associated with benign prostatic hyperplasia and constipation. Acquired hernias may also occur from weakness caused by a previous surgical incision (incisional hernias). Interestingly, evidence has emerged of a positive correlation between abdominal wall hernias and the development of abdominal aortic aneurysms (AAAs). Patients undergoing AAA repairs are more likely to develop inguinal and incisional hernias; this suggests a common underlying defect in collagen metabolism in affected patients (Antoniou et al., 2010).
Complications of abdominal wall hernias
Hernias may be reducible, incarcerated, obstructed or strangulated. They may also be primary, in the absence of any previous hernia, or recurrent, following a previous attempted repair.
A reducible hernia is one which returns freely back into its original cavity. Hernias may reduce spontaneously when intra-abdominal pressure is reduced and the abdominal wall musculature is relaxed (e.g. when the patient lies down) or may be reduced manually by applying gentle pressure (sometimes more easily achieved by asking the patient to reduce it themselves!).
A hernia may be fully or partially irreducible (incarcerated) when it does not return freely into its original cavity. This in itself is not necessarily a worrying feature. The longer the hernia spends outside its original cavity, the more likely it is to become irreducible, as a result of the hernia sac developing adhesions (connective tissue) with the neck of the hernia and surrounding tissue. However, if a hernia becomes acutely incarcerated and painful (for example, following a straining episode), then it must be referred urgently for surgical assessment (see Fig. 3).
Incarcerated paraumbilical hernia.
An obstructed hernia is one in which the hernia sac contains small bowel that becomes obstructed within the neck of the hernia but remains viable. Abdominal wall hernias are one of the commonest causes of acute small bowel obstruction (the others being intra-abdominal adhesions from previous surgery and malignancy) and should always be sought on examination. The patient typically presents with an acutely painful, irreducible hernia and a distended abdomen, in which vomiting may be a prominent feature. In the case of a proximal small bowel obstruction, the vomitus may appear bile-stained, having a green or yellow tinge. However, vomitus from a distal small bowel obstruction may be very dark brown / black and foul-smelling (‘faeculent’) and in the authors’ experience, may be initially mistaken for haematemesis in the acutely unwell patient. A ‘closed loop’ small bowel obstruction is a variant that occurs when both afferent and efferent loops of small bowel within a hernia become obstructed. Hence, the small bowel segment is obstructed at both ends and quickly becomes strangulated. Obstructed hernias may quickly become strangulated as the small bowel's blood supply through the neck of the hernia is gradually compromised. They should, therefore, be promptly referred.
Strangulation refers to an acute compromise in blood supply to the hernia contents. A small bowel may quickly become necrotic and perforate. An acutely painful hernia requiring opioid analgesia should therefore always be assessed for strangulation causing ischaemia of the hernia contents. However, this cannot be conclusively determined until surgery, when the hernia contents (e.g. small bowel) can be directly inspected to determine their viability (see Fig. 4). The requirement for a small bowel resection at surgery in addition to the hernia repair significantly increases the morbidity and mortality of the patient.
An incarcerated hernia may progress to obstruction and then strangulation, in which the hernia contents become non-viable, increasing the likelihood that a laparotomy and small bowel resection is required.
Presentation and diagnosis
The majority of hernias are diagnosed on the basis of history and examination findings. Occasionally, if a small or ‘occult’ hernia is suspected or not obvious on examination, further imaging may be required in the form of ultrasound, computed tomography (CT) or magnetic resonance imaging.
History
Hernias may be asymptomatic, and noted incidentally on abdominal examination, or on a CT scan performed for other reasons. Asymptomatic hernias in their early stages tend to be fully reducible, with a wide neck that allows the hernia to pass in and out freely. Hernias tend to become increasingly symptomatic over time. The patient may complain of an increasing ‘ache’ in the region of the hernia, worse towards the end of the day or following activity and improved on lying down or when the swelling is reduced. Hernias typically become more painful as the hernia content (e.g. small bowel) becomes increasingly pinched by the neck of the hernia, or their blood supply becomes compromised. Alternatively, they may present acutely as an emergency after a sudden rise in intra-abdominal pressure (e.g. a coughing fit or strenuous exercise), in which the hernia contents are forcibly pushed through a tight neck with resulting development of ischaemia.
Examination
Differential diagnosis of abdominal wall hernia.
Inguinal hernia
Inguinal hernias are the most common type of abdominal wall hernia, being seen in both men and women; they occur when the hernia sac protrudes along the inguinal canal. The inguinal canal is an oblique passageway through the anterior abdominal wall over the medial half of the inguinal ligament. In men, the relatively larger canal conveys the spermatic cord to the testis. In women it is smaller and conveys the round ligament, between the uterus and labium major. Inguinal hernias are said to be indirect if they pass through the deep inguinal ring and along the inguinal canal, or direct, if they bulge into the posterior aspect of the inguinal canal. Historically, differentiating between the two was made on the basis that indirect hernias were thought to be more likely to develop complications. However, differentiating between the two is often clinically very difficult. In men, both indirect and direct hernias may progress into the scrotum with time, forming an inguinoscrotal hernia. In women, inguinal hernias may present with swelling of the labia majora. In both men and women, inguinal hernias may be differentiated from femoral hernias by their position in relation to the pubic tubercle. Inguinal hernias always originate above (and medial) to the pubic tubercle, whereas femoral hernias always originate below (and lateral) to the pubic tubercle. Very small inguinal hernias are often difficult to diagnose on clinical examination. They may initially present with groin pain alone and further imaging may be required to differentiate them from musculoskeletal causes.
Femoral hernia
Femoral hernias are less common overall than inguinal hernias; they occur more commonly in women than men and are more likely to result in complications. The classic presentation is an elderly female patient with a virgin abdomen who presents with small bowel obstruction. Examination of the groins reveals an obstructing femoral hernia. Femoral hernias occur through the femoral ring, the upper part of the femoral canal, lying in the very medial aspect of the groin, that between the femoral vein laterally and the lacunar ligament of the pubis medially. Clinically they form a palpable lump below and lateral to the pubic tubercle. They can be difficult to distinguish clinically from inguinal hernias, therefore, it is recommended that all groin hernias in women should be referred as urgent (Nilsson et al., 2007).
Paraumbilical hernia
Hernias in the abdominal anterior or anterolateral wall are collectively known as ventral hernias, and include paraumbilical, umbilical, epigastric, spigelian and incisional hernias. Paraumbilical hernias are the commonest type of ventral hernia and occur via defects alongside the umbilical stalk. They are more common in women. They have a higher tendency to develop complications, and therefore, should be referred for surgical repair. True umbilical hernias are less common. They are herniations through the centre of the umbilical stalk and occur in two main groups of patients. The first are neonates, where there is a congenital defect present in the umbilical ring. The second group is adults with longstanding ascites, commonly due to advanced liver disease, where there is a gradual unravelling of the layers umbilical stalk due to longstanding increased intra-abdominal pressure. In neonates, the defect commonly closes spontaneously by 2 years of age and should only be operated on before this if the hernia becomes strangulated. In adults with chronic ascitie, the ‘hernia’ usually comprises skin with underlying ascitic fluid rather than small bowel. Even so, as these patients typically have significant co-morbidity, they are not appropriate candidates for surgical repair and should be managed non-operatively where possible.
Epigastric hernia
Epigstric hernias occur in the upper abdomen, between the xiphisternum and the umbilicus, and are typically seen in middle-aged men. They have a lower tendency to develop complications. They should not be confused with a rectus abdominus divarication (or diastasis), seen typically in obese patients, where the rectus strap muscles are forced apart, but the underlying fascia remains intact. The latter do not require surgical repair and should not be referred for such.
Spigelian hernia
Spigelian hernias are rare and occur laterally, just below the level of the umbilicus. The defect is a weakness between the lateral border of the rectus abdominus muscle (the linea semilunaris) and the arcuate line (a horizontal line just below the umbilicus that demarcates the lower aspect of the posterior border of the rectus sheath). Spigelian hernias tend to be small, but have a higher risk of complications.
Lumbar hernia
Lumbar hernias are uncommon hernias occuring posteriorly through the lumbar triangles (costo-iliac spaces). They tend to occur in older men, are usually left sided and may contain retroperitoneal viscera such as the kdney, ureter and pancreas.
Incisional hernia
Incisional hernias occur at the site of a previous surgical incision. They arise because scar tissue provides only around 70–80% of the strength of the original tissue, 6 months after repair. They are especially common in the abdominal midline, occurring in up to 20% of patients following midline laparotomy (Paterson-Brown and Paterson, 2018). They may also occur through port sites following laparoscopic surgery. They are more likely to occur following wound infections and emergency procedures and have a higher tendency to develop complications.
Parastomal hernia
A parastomal hernia is a form of incisional hernia, in which the hernia protrudes through the defect in the musculofascial layer originally created for the stoma. They have a high risk of complications and frequently recur when repaired.
Imaging
Both ultrasound and cross-sectional imaging complement history and examination in the diagnosis of an abdominal wall hernia and may be required to differentiate a hernia from the other causes of abdominal lumps and bumps. Ultrasound is useful in children, as it avoids ionising radiation. It is also dynamic, and in adults the sonographer may be able to demonstrate a hernia as the patient performs the Valsalva manouevre. CT is useful in the emergency scenario to confirm whether a hernia is present, especially in patient with large body habitus who may be difficult to examine. It is also used to determine whether a hernia is acutely obstructed or strangulated and can detect other causes of small bowel obstruction in patients with an incidental hernia such as adhesions from previous surgery. CT is also being increasingly used pre-operatively in patients with large or complex incisional hernias, to allow preoperative planning for operative repair. In particular, three-dimensional reconstructions of the abdomens of such patients may be used to assess the size of the defect, the presence and quality of surrounding muscular layers, and the proportion of viscera within the hernia rather than within the abdomen cavity (Fig. 5).
Axial CT image of a large left lateral incisional hernia containing multiple loops of small bowel. The original incision was in the left lower abdominal quadrant from elective colostomy closure. The patient originally underwent emergency laparotomy, sigmoid colon resection and end colostomy (Hartmann's procedure) for perforated sigmoid diverticular disease. Such hernias require careful pre-operative planning and patient optimisation prior to surgery.
Management of abdominal wall hernias
The management of a hernia will depend on whether the hernia is symptomatic and whether it presents electively or as an emergency. All acutely painful hernias should be assessed urgently and referred to the on-call general surgical team if thought to be obstructed or strangulated. However, minimally symptomatic or asymptomatic hernias may be referred routinely to the general surgery out-patient clinic, where they may be formally diagnosed and monitored over time (‘watchful waiting’). Many asymptomatic hernias will become increasingly symptomatic over time. For example, follow-up studies of asymptomatic inguinal hernias have shown that the watchful waiting approach results in surgery in 70% of patients in this group by 5 years (Fitzgibbons et al., 2013). Some surgeons may, therefore, advocate repair of asymptomatic or minimally symptomatic inguinal hernias as being most cost-effective.
Non-operative management
In patients who are unfit for surgery, or who do not want surgery after appropriate information has been provided, a hernia support may help to ease symptoms and keep the hernia reduced. Such devices include a hernia truss for inguinal hernias or abdominal wall binder for ventral hernias. These may also be useful in patients who are being considered for surgery but first require a period of pre-operative optimisation (e.g. smoking cessation therapy or weight loss), or post-operatively to reduce the risk of seroma.
Operative management
Most acutely painful hernias will require urgent operative intervention to prevent strangulation of the hernia contents. However, if strangulation does occur, the patient requires a bowel resection in addition to repair of the hernia, which significantly increases morbidity and mortality. Such a procedure would usually require open surgery or possibly a full midline laparotomy if a small bowel resection is required. Elective symptomatic hernias are more likely to be repaired laparoscopically and as a day-case, conferring all the usual benefits of minimally invasive surgery.
The principles of operative repair of hernias are largely the same regardless of whether the patients present electively or as an emergency. The hernia sac is freed from the neck and from surrounding tissue and before being reduced the sac is typically opened to ensure that the contents (potentially small bowel) are viable. The sac is then closed and the hernia reduced. The defect in the abdominal wall must then be repaired, either with sutures alone or with a combination of sutures and mesh. If a small bowel resection is performed, the defect is usually repaired with sutures alone, as using mesh in the presence of potential bowel content risks the possibility of a mesh infection. In elective surgery, mesh repair results in a significantly lower recurrence rate compared with using sutures alone.
The recovery period following elective abdominal wall surgery varies according to the size and complexity of the procedure and individual fitness of the patient. Convalescence following abdominal wall surgery is of socioeconomic importance. For most straightforward primary inguinal hernia repairs, 1 to 2 weeks should be adequate. Pain is the most common cause of a delay in returning to work, followed by wound complications (Bay-Nielsen et al., 2004).
Elective referral of the symptomatic hernia and individual funding requests
Clinical Commissioning Groups (CCGs) commission most of the hospital elective services in the local areas for which they are responsible. Due to acute financial pressures, CCGs in some regions have attempted to reduce their spending on procedures they consider to be of low clinical value, including inguinal hernia repairs. They have, therefore, introduced guidelines limiting which symptomatic hernia patients may be referred for consideration of surgical repair. Many GPs will be already familiar with such individual funding requests. In such cases, even if a patient is experiencing significant symptoms from their hernia and a GP wishes to refer them for surgical repair, further criteria may have to be fulfilled which justifies their ‘exceptionality’ over other patients with hernias and who have not been referred. These criteria may include a history of painful incarceration, or the hernia increasing in size from month to month (which interestingly bears no correlation with likelihood of strangulation). Unsurprisingly, therefore, a recent review has suggested that this stricter approach by some CCGs produces worse clinical outcomes by increasing the risk of strangulation, and is less cost-effective (Nilsson et al., 2007; Orchard et al., 2016).
Post-operative complications
Patients undergoing hernia surgery may present to their GPs in the days or weeks following surgery with a number of potential complaints, including pain or swelling at the site of surgery. The following complications should be considered.
Haematoma
A haemamtoma often occurs following inguinal hernia surgery, or surgery which has involved a large amount of soft tissue dissection. It presents as a firm lump deep to the wound and in inguinal hernia repair, may be associated with quite significant purple / blue scrotal-skin discolouration. The diagnosis is made clinically or confirmed with ultrasound. Haematomas are managed conservatively, unless they become infected where they may require a wound washout and course of antibiotics.
Seroma
Seromas are fluctuant fluid-filled collections developing in the space previously occupied by the hernia, and usually occur following a large amount of soft-tissue dissection. They are usually asymptomatic and tend to recur if aspirated. Numerous surgical strategies are employed to reduce the risk of seroma, including the use of suction drains or abdominal wall binders post-operatively to attempt to reduce the amount of dead-space that remains following hernia repair.
Chronic groin pain
Chronic groin pain is pain that is present for more than 6 months following inguinal hernia surgery, occurring in approximately 5% of open mesh repairs, and slightly lower in those performed laparoscopically. There is increasing evidence the pain is neuropathic in origin and may be helped with the use of low-dose amitryptiline and other neuropathic analgesics (Simons et al., 2018).
Hernia recurrence
An early hernia recurrence within the first few weeks results from failure of the surgical repair and can be differentiated from other causes of wound swelling such as haematoma or seroma by ultrasound. Longer term recurrence risk is associated with obesity and wound complications.
KEY POINTS
An abdominal wall hernia is the abnormal protrusion of an intra-abdominal viscus, frequently small bowel, through a defect in the abdominal wall musculature The most common abdominal wall hernias seen in general practice are inguinal, ventral and femoral hernias Abdominal wall hernias may be reducible, incarcerated, obstructed or strangulated All acutely symptomatic hernias should be urgently referred to exclude strangulation of the hernia contents which may result in a significant increase in morbidity and mortality Asymptomatic abdominal wall hernias require referral only if at high risk of complications, such as femoral hernias; otherwise, they can undergo ‘watchful waiting’ in the community and may benefit from trusses or abdominal wall supports Mildly symptomatic hernias without suspected complications may be referred electively and may require an individual funding request from the regional CCG
