An inguinal hernia occurs when abdominal cavity contents enter into the inguinal canal.
They are the most common type of hernia and account for around 75% of all anterior abdominal wall hernias, with a prevalence of 4% in those over 45 years.
In this article, we shall look at the classification, clinical features and management of inguinal herniae.
A hernia is defined as the protrusion of part or whole of an organ or tissue through the wall of the cavity that normally contains it.
For the inguinal herniae, there are two main subtypes that can occur:
- Direct inguinal hernia (20%) – Bowel enters the inguinal canal “directly” through a weakness in the posterior wall of the canal, termed Hesselbach’s triangle
- They occur more commonly in older patients, often secondary to abdominal wall laxity or a significant increase in intra-abdominal pressure
- Indirect inguinal hernia (80%) – Bowel enters the inguinal canal via the deep inguinal ring
- They arise from incomplete closure of the processus vaginalis, an outpouching of peritoneum allowing for embryonic testicular descent, therefore are usually deemed congenital in origin
These two types of inguinal hernia can only be reliably differentiated at the time of surgery by identifying the inferior epigastric vessels – indirect hernias will be lateral to the vessels whilst direct hernias will be medial to the vessels.
The main factors that increase the risk of developing an inguinal hernia:
- Increasing age
- Raised intra-abdominal pressure, from chronic cough, heavy lifting, or chronic constipation
The most common presenting symptom is a lump in the groin, which (for reducible hernia) will initially disappear with minimal pressure or when the patient lies down. There may be mild to moderate discomfort which can worsen with activity or standing.
If the hernia becomes incarcerated, it can become painful, tender, and erythematous. The patient may also present with clinical features of bowel obstruction if the bowel lumen becomes blocked, or with features of strangulation* if the blood supply becomes compromised.
*A hernia that has strangulated will present as an irreducible and tender tense lump, with the pain often being out of proportion to clinical signs; this may be accompanied with clinical features of obstruction
When examining any groin lump, specific features to note for any suspected inguinal hernia include:
- Cough impulse – remember that an irreducible hernia may not have a cough impulse
- Location – inguinal (superomedial to the pubic tubercle) or femoral (inferolateral to the pubic tubercle)*
- Reducible – On lying down +/- minimal pressure
- If it enters the scrotum, can you get above it / is it separate from the testis
*This is not always clear on examination, especially if large and tender
Differentiation of Inguinal Hernia
Theoretically, to differentiate a direct from an indirect inguinal hernia, the examiner must reduce the hernia and then place pressure over the deep inguinal ring (located at the mid-point of the inguinal ligament), before asking the patient to cough.
If the hernia protrudes despite occlusion of the deep inguinal ring, this indicates a direct hernia, whereas if the hernia does not protrude, this indicates an indirect hernia. However, this assessment is often seen as unreliable and the only definite method to differentiate them is at the time of surgery.
A hernia is typically a clinical diagnosis. Current Royal College of Surgeons Guidelines state that imaging should only be considered in patients if there is diagnostic uncertainty or to exclude other pathology.
If necessary, an ultrasound scan is recommended as first line imaging in the outpatient setting. For patients with features of obstruction or strangulation, CT imaging will be required.
Any patient with a symptomatic inguinal hernia (significant mass or discomfort) should be offered surgical intervention (see below).
The risk of strangulation is no more than about 2% per year with an inguinal hernia. Any patients presenting with evidence of strangulation (such as pain out of proportion to clinical features or deranged biochemical results) nearly always require urgent surgical exploration.
A third of patients with an inguinal hernia will never experience any symptoms and most of these patients can be managed conservatively, however discussion should take place around the likelihood of future surgical intervention and the symptoms of potential strangulation.
Hernia repairs can be performed via open repair (Lichtenstein technique most commonly used) or laparoscopic repair (either total extraperitoneal (TEP) or transabdominal pre-peritoneal (TAPP)).
Open mesh repairs are preferred for those with primary inguinal hernias and are deemed the most cost-effective technique in this patient group. They can be performed under general, spinal or local anaesthesia, dependent on patient fitness and surgeon preference.
A laparoscopic approach is preferred* in those with bilateral or recurrent inguinal hernias. It can also be considered in certain patients with a primary unilateral hernia, mainly those at a high risk of chronic pain (young and active, previous chronic pain, or with a predominant symptom of pain) or in females (due to the increased risk of the presence of a femoral hernia).
*Laparoscopic repairs are associated with longer operating times but quicker post-operative recovery, fewer complications, and less post-operative pain.
Emergency Management of a Hernia
The serious complications of a hernia that require urgent intervention are:
- Irreducible / incarcerated – the contents of the hernia are unable to return to their original cavity
- Obstruction – the bowel lumen has become obstructed, leading to the clinical features of bowel obstruction
- Strangulation – compression of the hernia has compromised the blood supply, leading to the bowel becoming ischaemic
A strangulated hernia is a surgical emergency, due to the time-dependent risk of bowel infarction.
The diagnosis is typically a clinical one and requires urgent surgical exploration; due to the time critical nature of the condition, rarely will further imaging be requested.
The specific management for strangulated hernia will vary depending on the type of hernia involved. Mortality is much higher in emergency cases compared to elective operations for all hernia.
The main complications of an inguinal hernia are incarceration, strangulation, and obstruction.
Post-operative complications of hernia repair include:
- Pain, bruising, haematoma, infection, or urinary retention
- Recurrence, approximately 1.0% within 5 years of surgery
- Chronic pain (persisting 3 months after hernia repair), can occur in up to 30% patients and is disabling in ~2%
- Damage to vas deferens or testicular vessels, leading to ischaemic orchitis (and potentially sub-fertility)
- An inguinal hernia can be classified as direct or indirect
- The diagnosis is a clinical one and only warrants further investigation if there is diagnostic uncertainty
- Most cases are repaired via open approach, unless bilateral or recurrent