The inguinal canal is a short passage that extends inferiorly and medially through the inferior part of the abdominal wall. It is superior and parallel to the inguinal ligament, and serves as a pathway by which structures can pass from the abdominal wall to the external genitalia. This makes it of great clinical importance, as it is a common site of herniation. In this article, we will look at the anatomy of the inguinal canal: from its development and borders to its contents and clinical relevance.
During development, the tissue that will become gonads (either testes or ovaries) establish in the posterior abdominal wall, and descend through the abdominal cavity. A fibrous cord of tissue called the gubernaculum attaches the inferior portion of the gonad to the future scrotum or labia, and guides them during their descent. The inguinal canal is the pathway by which the testes (in an individual with an XY karyotype) leave the abdominal cavity and enter the scrotum. In the embryological stage, the canal is flanked by an out-pocketing of the peritoneum (processus vaginalis) and the abdominal musculature.
The processus vaginalis normally degenerates, but a failure to do so can cause an indirect inguinal hernia, a hydrocele, or interfere with the descent of the testes. The gubernaculum (once it has shortened in the process of the descent of the testes) becomes a small scrotal ligament, tethering the testes to the scrotum and limiting their movement. Individuals with an XX karyotype also have a gubernaculum, which attaches the ovaries to the uterus and future labia majora. Because the ovaries are attached to the uterus by the gubernaculum, they are prevented from descending as far as the testes, instead moving into the pelvic cavity. The gubernaculum then becomes two structures in the adult- the ovarian ligament and round ligament of uterus.
The inguinal canal has four borders - anterior, posterior, roof, and floor. Anteriorly, the canal is bounded by the aponeurosis of the external oblique. The posterior boundary is formed by the transversalis fascia. The roof of the canal is formed by the internal oblique and transversus abdominis muscles, while the floor is formed by the inguinal ligament. The mid-inguinal point is a useful anatomical landmark, at the midpoint of the inguinal ligament.
The inguinal canal contains the spermatic cord (biological males only) and round ligament (biological females only). Additionally, two nerves pass through the canal - the ilioinguinal nerve and the genital branch of the genitofemoral nerve.
A hernia is defined as the protrusion of an organ or fascia through the wall of a cavity that normally contains it. During periods of increased intra-abdominal pressure, the abdominal viscera are pushed into the posterior wall of the inguinal canal. To prevent herniation of viscera into the canal, the muscles of the anterior and posterior wall contract, and ‘clamp down’ on the canal. Inguinal hernias form either through congenital defects in the abdominal wall or due to increased intra-abdominal pressure and weakened abdominal wall, for example due to pregnancy or straining.
Indirect hernias occur when a portion of the small intestine passes through the internal ring of the inguinal canal (the opening to the canal) and into the scrotum. Direct hernias occur when the small intestine passes through the posterior wall of the inguinal canal, instead of the internal ring. Indirect hernias are most common in men, while women are more likely to experience direct hernias. Both indirect and direct hernias can occur in either sex, however.
Inguinal hernias should not be taken lightly, as they can cause pain, intestinal obstruction or strangulation. Treatment typically involves surgical repair, in which the hernia is pushed back into the abdominal cavity and the weakened area of the abdominal wall is surgically reinforced. The surgeon may use a mesh patch to provide additional support to the area, preventing recurrence of the hernia.
The inguinal canal is an important anatomical structure, connecting the abdominal wall with the external genitalia. It is of great clinical relevance as a potential weakness in the abdominal wall, and thus a common site of herniation. Understanding the anatomical borders, contents and clinical relevance of this structure is essential for diagnosis and treatment of inguinal hernia, as well as any other hernias of the abdominal wall.
Hernias involving the inguinal canal can be divided into two primary categories.
Both types of inguinal hernia can present as lumps in the scrotum or labia majora.
During the development of the inguinal canal, the tissue which will become the gonads (ovaries or testes) establish in the posterior abdominal wall and begins to descend through the abdominal cavity. To aid this process, a fibrous cord of tissue called the gubernaculum attaches the inferior portion of the gonad to the future scrotum or labia majora and helps guide them. The inguinal canal is the pathway by which the testes exit the abdominal cavity and enter the scrotum. At this stage, it is flanked by an out-pocketing of the peritoneum (the processus vaginalis) and the abdominal musculature. Normally, the processus vaginalis will degenerate; however, if it fails to do so, it can cause an indirect inguinal hernia, a hydrocele, or interfere with the descent of the testes. The gubernaculum shortens during the descent of the testes and becomes a small scrotal ligament, tethering the testes to the scrotum and limiting their movement.
In individuals with an XX karyotype, the gubernaculum attaches the ovaries to the uterus and the future labia majora. Because the ovaries remain attached to the uterus by the gubernaculum, they are prevented from descending as far as the testes, instead moving into the pelvic cavity. Following this process, the gubernaculum becomes two structures in the adult: the ovarian ligament and round ligament of uterus.
In this article, two terms are often mentioned, and confused with one another. These terms are the mid-inguinal point and the midpoint of the inguinal ligament.
The inguinal canal is bordered by four walls; anterior, posterior, superior (roof) and inferior (floor). There are two openings to it, the superficial and deep rings.
At times of increased intra-abdominal pressure, the abdominal viscera are pushed into the posterior wall of the inguinal canal. To prevent herniation of viscera into the canal, the muscles of the anterior and posterior walls contract and ‘clamp down’ on the canal.
The two openings to the inguinal canal are known as rings, one deep (internal) and one superficial (external).
The inguinal canal is a triangle-shaped opening formed by the invagination of the external oblique, containing intercrural fibres. These fibres run perpendicular to the aponeurosis of the external oblique and prevent the ring from widening. The contents of the inguinal canal vary between anatomical sexes.
The inguinal canal is an important structure of the lower abdominal wall, which begins embryologically from the deep inguinal ring and extends to the midpoint of the inguinal ligament, known as the mid-inguinal point. This canal is comprised of four distinct boundary walls - anterior, posterior, floor, and roof. The anterior wall is composed of the external oblique and the transversalis fascia, while the posterior wall is made up of the transversalis fascia alone. The roof is formed by the internal oblique and the transversalis fascia, and the floor is formed by the transversalis fascia, conjoint tendon, and the external oblique aponeurosis. The spermatic cord, round ligament, ilioinguinal, and genitofemoral nerves pass through the inguinal canal.
The walls of the inguinal canal are generally collapsed and serve to help prevent other structures from entering and becoming stuck in the canal. Clinically, hernias within the inguinal canal can be divided into two main categories: indirect hernias, which enter through the deep inguinal ring, and direct hernias which pass through the posterior wall of the inguinal canal. Indirect hernias are more common in males, and are often caused by a weakened or stretched inner wall of the abdominal cavity, which allows a loop of the intestines to protrude through to the inguinal canal.
Direct hernias enter through the posterior wall of the canal and are due to a weaken or deficient posterior wall. Unlike indirect hernias, direct hernias can sometimes enter through the indirect inguinal ring as well as through the posterior wall of the inguinal canal. Direct herniae are also more common in women than in men.
In either case, a hernia can cause significant discomfort and can lead to additional issues if untreated. If a hernia occurs, it is important to seek medical attention in order to prevent further injury or complications. A physician will be able to determine the best course of treatment for the hernia.
The inguinal canal and hernias within it are clinically relevant and should be understood by healthcare professionals. Knowing the anatomy of the canal and the two types of herniat can help in providing the best possible care for patients with inguinal issues.
