The inguinal canal is an exam favourite…
The inguinal canal is a frequent topic in the MRCEM Part A, and will no doubt remain a regular feature of the new FRCEM Primary exam. It is therefore worth taking the time to develop a sound understanding of the inguinal canal; including the contents, boundaries, anatomical landmarks and clinical relevance.
The RCEM Basic Science Curriculum states the following as required knowledge:
- Knowledge of the inguinal region enables understanding of the basis of hernias as well as the procedural anatomy of line placement and regional nerve blockade.
- Knowledge of the inguinal canal:
- Roof, walls and floor
- Origin of the superficial inguinal ring
- Origin of the deep inguinal ring
- Anatomical relations of the nerves, arteries & veins in the inguinal region and the position of psoas
Teachmeanatomy is a useful resource covering the development and anatomy of the inguinal canal to the level of detail required for the FRCEM Primary.
The following video is a great reminder of the anatomy of the inguinal canal, its relations and its boundaries. (Video courtesy of Access Anatomy)
A useful mnemonic to remember the structures that contribute to the walls of the inguinal canal is 2MALT:
From superior to posterior:
- Superior wall (roof): 2 Muscles
- internal oblique Muscle
- transversus abdominus Muscle
- Anterior wall: 2 Aponeuroses
- Aponeurosis of external oblique
- Aponeurosis of internal oblique
- Lower wall (floor): 2 Ligaments
- inguinal Ligament·
- lacunar Ligament
- Posterior wall: 2Ts
- Transversalis fascia
- conjoint Tendon
Another useful mnemonic for remembering the contents of the canal is:
Sperm IN Ringer Lactate
Spermatic Cord (in males)
IlioiNguinal nerve (in both sexes)
Round Ligament (in females)
The main clinical importance of the inguinal canal relates to inguinal hernias.
Inguinal hernias can be subdivided into:
- Direct – the peritoneal sac enters the canal through the posterior wall.
- Indirect – the peritoneal sac enters the canal through the deep inguinal ring.
Direct inguinal hernias are acquired due to a weakening in the abdominal wall in a region known as Hesselbach’s triangle. This allows the peritoneal sac to protrude into the canal through the posterior wall. The sac is medial to the inferior epigastric vessels. Direct inguinal hernias are ten times more common in men compared to women, and tend to occur in the middle-aged and elderly as the abdominal wall weakens.
Indirect inguinal hernias are congenital in nature, resulting from the failed closure of some part, or all, of the embryonic processus vaginalis. An indirect hernia enters the inguinal canal at the deep inguinal ring, lateral to the inferior epigastric vessels. It passes inferomedially emerging via the superficial ring. Indirect hernias are the most common groin hernia.