Inguinal Region and Hernias

• A hernia is a bulge created by the rupture of a containing organ.
• An abdominal hernia involves a protrusion of peritoneum through the abdominal boundaries (diaphragm, abdominal walls, pelvic floor).

  Abdominal hernias arise in weakened areas, such as the umbilicus and the linea alba.
• The umbilicus is an area of weakness in the abdominal wall because this was the region where the wall of the abdomen was breached during development in order for the foetus to be connected to the placenta via the umbilical cord.
• The linea alba is considered a weakness in the abdominal wall because the linea alba is formed from the raphe of interdigitating tendons of the anterior muscles.
• Hernias may occur in the abdomen because the pressure inside the abdominal cavity is greater than the outside, and there is a weakness of the abdominal wall.
• An abdominal hernia may just be a protrusion of the peritoneum, or it may contain viscera, such as a loop of bowel.

  If the hernia does contain viscera, then the supply of blood to the viscera within the hernia could become compromised. This can result in necrosis of the tissue isolated in the hernia due to a lack of oxygen and nutrients. This type of hernia is known as a strangulated hernia.
• There are various types of abdominal hernias:

  • umbilical hernias
  • epigastric hernias
  • paraumbilical hernias
  • suprapubic hernias
  • Spigelian hernias (hernias in the region of the linea semilunaris).
  • lumbar hernias (hernias through the lumbar fascia).
  • incisional hernias (hernias through weakness in the abdominal wall due to surgery or stab wounds).
  • Hiatus hernias (hernias through the oesophageal hiatus in the diaphragm).
  • Inguinal hernias
  • Femoral hernias
• Inguinal hernias and femoral hernias are the most common type of abdominal hernia.

  Umbilical hernias, epigastric hernias, paraumbilical hernias, and suprapubic hernias are occur down the midline (linea alba) of the abdomen.
• Umbilical hernias can either be congenital or acquired.
• The umbilicus represents a natural hernia that occurs in the uterus, because there may not be enough space within the foetal abdominal cavity to contain the viscera as it elongates and develops. Usually these hernias close up, but an umbilical hernia after birth is usually due to the umbilical scar failing to close. This is a congenital umbilical hernia.
• Adult hernias are usually acquired hernias. Ways in which hernias can be acquired are through:

  • multiparity - a woman giving birth multiple times. This can cause the abdominal wall to weaken with each birth.
  • Abdominal pathologies
  • Obesity
• Small umbilical hernias less than 1cm in diameter, and most childhood hernias tend to close spontaneously. Adult hernias, or larger hernias may require surgical repair, especially in the case of strangulated hernias.
• Behind the inguinal ligament, there is a vascular bundle that supplies the lower limb, consisting of the femoral vein, femoral artery, and the lymphatics. These vessels are contained within a sheath called the femoral sheath.

  Each vessel has it's own compartment, and the femoral artery and the femoral vein are solidly contained within their respective compartments. The lymphatics however, are thin vessels surrounded by fat, and the remaining space inside this compartment is known as the femoral canal.
• Below the inguinal ligament, there is an opening in the deep fascia where superficial veins and superficial lymphatics can join the deep vessels within the femoral sheath. This opening is called the saphenous opening.
• The femoral nerve doesn't pass through the femoral sheath with the vasculature. Instead, it continues downwards, 4cm below the inguinal ligament, and disappears by blending into the adventitia (outer layer of fibrous connecting tissue surrounding an organ/tissue) of the femoral vessels.
• The femoral canal is a weak spot, so a femoral hernia is a protrusion through the femoral canal and out through the saphenous opening. The femoral hernia shows as a bulge in the thigh. Femoral hernia are more common in females than males because females have a wider pelvis, and hence, have a wider femoral canal.
• At the medial end of the inguinal ligament, there is another ligament that curves back sharply onto the pelvis. This is the lacunar ligament. The lacunar ligament acts as a harsh cutting edge to any femoral hernia, and may compress them at this point, turning the hernia into a strangulated femoral hernia.
• The inguinal canal is a canal located just above the inguinal ligament. The reason this region is a weak spot in the abdomen is because there is a gap created for the descent of the gonads. The ovaria never use this gap because the inguinal canal was created before the gonads sufficiently formed.
• In males, the inguinal canal is the route taken by the testes to meet the scrotum. Specifically, the inguinal canal functions to connect the spermatic cord from the testes in the scrotum to the pelvic cavity.

  In females, the inguinal canal is used for the round ligament of the uterus to connect the labia majora of the external genitalia to the uterus within the pelvis.
• The entrance to the inguinal canal is created in the transversalis fascia deep in the abdominal wall. This entrance point is called the deep inguinal ring (or internal ring). The deep inguinal ring is located just lateral to the origin of the inferior epigastric artery, 1.25cm above the mid-point of the inguinal ligament. The deep inguinal ring is circular in shape.
• The exit of the inguinal canal is through the external oblique aponeurosis. This exit point is called the superficial inguinal ring (or external ring). The external oblique aponeurosis is attached to the pubic tubercle and the pubic crest; the gap between these attachments is the superficial ring, and this ring is triangular in shape.
• In the foetus and in early infancy, the deep inguinal ring and superficial inguinal ring lie close together. This alignment increases the chance of an inguinal hernia forming each time the intra-abdominal pressure increases. In comparison, in an adult, the inguinal canal is longer, and so the deep ring and superficial ring are further apart, so a hernia is less likely to form.
• When the pressure in the abdomen rises, there is an increased risk of herniation. However, since the inguinal ligament is oblique, an indirect hernia can't pass straight through. Instead, it has to pass along the plane of the inguinal canal, which is the abdominal wall itself. And since the wall is being compressed by the expanding abdomen (due to the rise in pressure), the passage for an indirect hernia is made more difficult.

  The obliquity of the inguinal canal reduces the chances of an indirect inguinal hernia forming.
• The inguinal canal has a roof, floor, and walls:

  • The roof is made up of the arched fibres of the conjoint tendon (made from the internal oblique and transversus abdominis aponeuroses).
  • The floor is made from the upturned lower border of external oblique abdominis (which forms the inguinal ligament).
  • The anterior wall is made from the external oblique aponeurosis and internal oblique abdominis (in the canal's lateral third).
  • The posterior wall is made from transversalis fascia and the conjoint tendon (in the canal's medial third).
• There are two types of inguinal hernias: indirect inguinal hernias and direct inguinal hernias.
• Indirect inguinal hernias are protrusions of the peritoneum (possibly with loops of bowel as well) into the deep inguinal ring, through the inguinal canal, and out through the superficial inguinal ring.

  The deep ring can be considered a weak spot because if internal oblique and external oblique (the layers that make up the anterior inguinal wall) are weak, and if the internal pressure in the peritoneal cavity is high enough, then the peritoneum may be allowed to enter the inguinal canal through the deep ring.
• A direct inguinal hernia is a protrusion of the peritoneum straight through a specific weak spot in the abdominal wall, or a hernia that exits through the superficial inguinal ring, but doesn't enter through the deep inguinal ring.
• The weak spot in the anterior abdominal wall where direct hernias can occur is called the inguinal tringle (or Hesselbach's triangle). This is region protected only by transversalis fascia and the external oblique aponeurosis, with the latter providing no support at the superficial ring.
• The inguinal triangle has three borders: the medial border is rectus semilunaris, the lateral border is the inferior epigastric artery, and the inferior border is the inguinal ligament.

  The lower half of the inguinal triangle is particularly vulnerable to direct inguinal herniation because this specific region is only protected by transversalis fascia. To prevent herniation in this region, the conjoint tendon - located in the upper half of the triangle - is pulled down as it contracts, which adds a layer of protection.
• The muscles forming the conjoint tendon are internal oblique abdominis and transversus abdominis. These muscles are supplied y the ilioinguinal and iliohypogastric nerves from L1.

  Direct inguinal herniation is likely to occur should the lower fibres of the conjoint tendon become paralysed.
• An indirect hernia can often be felt emerging from the superficial ring by placing a finger into the scrotal wall. A small hernia may be reduced by pushing it back through the ring. However, not all inguinal hernias will pass through the length of the canal, such as the direct inguinal hernias that would end up passing through the inguinal triangle instead.
• The testis develops high up in the posterior abdominal wall, and is guided into the scrotum by a fibrous cord called the gubernaculum. The testis moves along the gubernaculum and as it moves, the proximal part behind disintegrates. By the time the testis have reached the scrotum, the small amount of the gubernaculum left becomes known as the scrotal ligament. The scrotal ligament attaches the testis to the scrotal wall.
• For the gubernaculum and the testis to get into the scrotum, layers of the abdominal wall have to be breached. And since the deep and superficial inguinal rings are more aligned in a foetus, this is a straight passage. The evaginations of these anterior abdominal layers will eventually form the spermatic cord.
• Formation of the spermatic cord starts with the indentation into the transversalis fascia - the deep inguinal ring. From the transversalis fascia, a layer of fascia is obtained. This layer is called the internal spermatic fascia.

  It then passes under the internal oblique, and receives a layer of fascia and muscle from internal oblique. These become known as the cremasteric fascia and cremasteric muscle respectively.

  The final layer that's breeched - external oblique - gives a layer of fascia to the developing spermatic cord known as the external spermatic fascia.
• The descending testis leaves a trail of the anterior abdominal wall layers wrapped around the ductus (vas) deferens and the neurovascular bundle. This structure is the spermatic cord.

  • The internal spermatic fascia is derived from transversalis fascia.
  • The cremasteric fascia and cremasteric muscle are both derived from internal oblique obdominis
  • The external spermatic fascia is derived from external oblique abdominis.
• Scarpa's fascia and Camper's fascia are both continuous with the scrotal wall. (Transversalis fascia, internal oblique, and external oblique are continuous with the spermatic cord).

  Scarpa's fascia becomes Colles' fascia, and superficial to that, Camper's fascia becomes continuous with Dartos muscle.
• The peritoneal cavity also starts to pass into the inguinal canal during the development of the spermatic cord. This forms a protrusion of the peritoneal cavity called the processus vaginalis. A terminal portion of the processus vaginalis buds off and forms the tunica vaginalis, which the testis is embedded in. The remainder of the processus vaginalis regresses, leaving behind a fibrous chord, and isolating the tunica vaginalis as a sac of serous fluid.
• Normally, the processus vaginalis closes and leaves behind a fibrous cord. However, in some cases, this may remain open, and form a connection between the peritoneal cavity and the tunica vaginalis. This is known as a patent processus vaginalis, meaning that fluid is allowed to move into the tunica vaginalis when intra-abdominal pressure increases.

  A patent processus vaginalis can also cause herniation of the abdominal content into the scrotum.
• The amount of serous fluid in the tunica vaginalis is often increased as a result of trauma to the scrotum or testis, or as a result of an infection of the testis, scrotum, or tunica vaginalis.

  The enlargement of the tunica vaginalis is known as hydrocele testis, which is felt as a painless swelling in the scrotum.

  There can also sometimes be a hydrocele of the processes vaginalis, which is usually isolated and harmless.