Hernias are a common surgical pathology that is poorly understood by medical students and junior trainees. Getting to grips with the underlying anatomy will hopefully provide you with the framework to be able to understand, diagnose and appreciate the principles of their management.
The often recited surgical definition of a hernia is ‘the protrusion of a viscus into an abnormal space’. In simple terms, a hernia describes a structure that passes through a space or defect, into an abnormal location.
This article will hopefully provide an overview of the more common abdominal hernias and a brief description of how they can be managed. Before we dive into the different types, I wanted to unpick some of the common terms used in relation to hernias (e.g. “56 year-old-male with an irreducible inguinal hernia”).
Reducible: when the contents of the hernia can be manipulated back into their original position through the defect from which they emerge
Incarcerated hernia (irreducible): the hernia is compressed by the defect causing it to be irreducible (i.e. unable to be pushed back into its original position)
Obstructed hernia: refers mainly to hernias containing bowel, where the contents of the hernia are compressed to the extent that the bowel lumen is no longer patent and causes bowel obstruction
Strangulated hernia: the compression around the hernia prevents blood flow into the hernial contents causing ischaemia of the tissues and associated pain
The most common type of abdominal hernia is an inguinal hernia, which typically presents with a lump in the groin. I think it is best to first look at the basic anatomy of the inguinal canal to aid the understanding of the clinical findings and then move on to the principles of management.
Anatomy of the inguinal canal
The inguinal ligament runs between the anterior superior iliac spine (ASIS) and the pubic tubercle (PT). Within this ligament runs a tube-like structure known as the inguinal canal. The function of this canal is to provide a passageway for abdominal contents to exit the abdomen. To be more specific, in males this is the spermatic cord (to facilitate ejaculation), and in females the round ligament. In both sexes, the canal also carries a sensory nerve known as the ilioinguinal nerve. The tube has an entry point from the abdominal cavity into the canal (deep inguinal ring) and an exit point (superficial inguinal ring) as it leaves the canal. The location of these two points is clinically important and is also a common exam question. The deep inguinal ring is located just above the mid-point of the inguinal ligament. The superficial ring lies just above and lateral to the pubic tubercle (see illustration below).
Deep vs superficial inguinal ring
Deep inguinal ring: just above the midpoint of the inguinal ligament
Superficial inguinal ring: just above and lateral to the pubic tubercle
Direct vs indirect inguinal hernias
An inguinal hernia is a protrusion of abdominal contents that ultimately emerges from the superficial inguinal ring. There are two main ways in which inguinal hernias can arise, which are discussed below.
Direct inguinal hernia
A direct inguinal hernia is caused by a weakness in the posterior wall of the inguinal canal. The abdominal contents (usually just fatty tissue, sometimes with bowel) are forced through this defect and enter the inguinal canal. This means that the contents emerge in the canal medial to the deep ring (as shown).
Indirect inguinal hernia
An indirect inguinal hernia, however, does not pierce the posterior wall. The abdominal contents pass through the deep inguinal ring, passing through the inguinal canal and exiting via the superficial ring.
Differences between indirect and direct inguinal hernias
Both types of hernias can exit via the superficial ring and emerge within the scrotum, however, it is more common for indirect inguinal hernias to do this as the path through both anatomical inguinal rings, rather than a muscle defect, has less resistance.
An appreciation of the anatomical differences can help to distinguish between the two using clinical examination. The principle of this is that if you can place your finger over the deep inguinal ring (just above the mid-point of the inguinal ligament), then you can control an indirect inguinal hernia which has been reduced. If when you press the deep ring, the hernia still protrudes, then the hernia is emerging via a defect in the posterior wall medial to this point and is, therefore, a direct hernia. It is useful to understand this clinical test as it helps remember the difference between the two. The clinical application of this kind of assessment, however, is limited as it is not very reliable and doesn’t change management.
What causes an inguinal hernia?
The easiest way to think about the causes of inguinal hernias is to think of:
Increased intra-abdominal pressure
Weakness of the abdominal muscles
The causes are, therefore, as follows:
How do hernias present?
Most commonly patients will present to their GP, with a painless swelling in the groin that develops over time.
The swelling is often otherwise asymptomatic and may come and go.
Alternatively, the swelling may have emerged suddenly after heavy lifting, for example.
Hernias can become symptomatic, presenting with clinical features such as:
Pain: particularly when coughing or stooping
Change in bowel habit
Burning sensation in the groin
Scrotal swelling (in males)
The majority of inguinal hernias can be accurately identified with a clinical examination. Where there is diagnostic uncertainty an ultrasound scan of the groin can help differentiate between other possible causes such as enlarged lymph nodes, fatty lumps, or vascular pathology.
So when and why do we fix them?
It is a common-sense approach with regards to the management of inguinal hernias. If the lump is small, not increasing in size and is asymptomatic the patient may wish to leave it alone. If however the hernia is causing pain or altering bowel habit then surgical management may be required. If the hernial contents become strangulated or obstructed this represents a surgical emergency and urgent operative fixation is required.
Both direct and indirect inguinal hernias are repaired in the same way. The main decision to be made is whether to fix the hernia via an open or a laparoscopic technique.
Open inguinal hernia repair
An open technique explores the inguinal canal, identifies the important structures within it (which need to be carefully protected), reduces the hernial contents back into the abdominal cavity and places a mesh that strengthens the posterior wall to prevent further herniation. It is a simple operation with excellent results and can be done with either general or local anaesthetic.
Laparoscopic inguinal hernia repair
Laparoscopic inguinal hernia repair is also an excellent operation in experienced hands. It has the added benefit of less post-operative pain and quicker recovery, particularly if bilateral hernia repair is performed. The basic steps of the operation involve visualising the defect from within the abdominal cavity, reducing or pulling back the contents of the hernia, and repairing the defect from within the abdomen.
Passing beneath the inguinal ligament are some important structures travelling to the upper leg. Most notably this includes the femoral artery, the femoral vein and the femoral nerve. The order in which these structures lie is easily remembered by the ‘NAVY VAN’ mnemonic. With the ‘Y’ signifying the creases of the groin, it illustrates how from lateral to medial the structures lie (nerve, artery, vein).
The femoral artery and vein are enclosed within a sheath (see diagram below). Lying medial to the femoral vein is a space known as the femoral canal. The function of this space is to allow expansion of the femoral vein in order to increase venous return. In health, the femoral canal contains just a small amount of fatty tissue and a lymph node (known as the lymph node of Cloquet).
This space, particularly in elderly women, can be a defect through which abdominal contents can protrude. It is important to note that this space is quite tight, and it is bordered medially by the sharp edge of the lacunar ligament. Therefore, femoral hernias are at high risk of strangulation and obstruction.