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Structure of the inguinal canal and femoral sheath.
Hello everyone! This is Megan from Kenhub, and welcome to another anatomy tutorial. In today's tutorial, we'll be covering the inguinal canal and related structures. We will start our tutorial by examining the lateral musculature of the anterior abdominal wall. As we will see, the abdominal oblique muscles and the transversus abdominis muscle contribute greatly to the formation of the walls of the inguinal canal. So, let's start with the external abdominal oblique muscles whose aponeurosis forms the inguinal ligament.
The origin of this muscle is on the fifth to twelfth ribs and the insertion of this muscle is on the iliac crest, the rectus sheath and the linea alba. This large anterolaterally-situated muscle is the largest of the three flat muscles of the lateral anterior abdomen. This muscle is innervated by the intercostal nerves 5 to 12. This muscle facilitates lateral flexion, rotation of the trunk, and the lowering of the thorax. Muscle fibers from the external abdominal oblique muscle also contribute to the walls of the inguinal canal. In fact, the aponeurosis of this muscle covers the anterior border of the canal and its medial crus contributes to the formation of the canal's superior border.
The internal abdominal oblique muscle is one of the three abdominal muscles we will discuss in this tutorial. It lies inferiorly to the external abdominal oblique and superficial to the transversus abdominis muscle. The origins of this muscle are on the thoracolumbar fascia, the iliac crest and the inguinal ligament. This muscle then inserts on the tenth to twelfth ribs and the rectus sheath. Innervation for this muscle comes from the intercostal nerves 8 to 12 as well as the iliohypogastric nerve and the ilioinguinal nerve.
The internal abdominal oblique functions to facilitate forward and lateral flexion and the lowering of the rib cage. The muscle's fleshy part covers the anterior border of the canal and its musculoaponeurotic portion contributes to the formation of the canal's superior border.
The third anterior lateral muscle of the abdominal wall we will discuss is the transversus abdominis muscle. It is the innermost of the three abdominal muscles, lying beneath the internal abdominal oblique. This muscle has points of origin on the seventh to twelfth ribs, the thoracolumbar fascia, and the iliac crest as well as the inguinal ligament. This muscle only has one insertion point which is the rectus sheath. The transversus abdominis muscle is innervated by the seventh to twelfth intercostal nerves as well as the iliohypogastric nerve, the genitofemoral nerve, and the ilioinguinal nerve. This muscle also contributes to the formation of the roof of the abdominal canal.
Now, let's further discuss the inguinal canal. The inguinal canal is an obliquely-situated tubular opening found on the anterior wall of the abdomen at an angle and running inferiorly and medially. It is about 3.5 to 5 centimeters long. It is bordered by the inguinal ligament, external oblique aponeurosis, the internal oblique muscle, the transverse abdominis muscle, and the interfoveolar ligament. The superficial inguinal ring and the deep inguinal ring form the entrance and exit of the inguinal canal respectively.
Moving on now to discuss the borders of the inguinal canal. The canal has a superior border – the roof, an inferior border or the floor, and a posterior border and an anterior border. So, now let's move on to discuss each of these borders individually.
The superior border of the inguinal canal is also referred to as the roof of the inguinal canal. This roof is made up of the medial crus of the aponeurosis of the external oblique muscle, the musculoaponeurotic arches of the internal oblique muscle and the transversus abdominal muscles as well as the transversalis fascia. The transverse fascia is an aponeurosis extending from the inguinal region to the diaphragm where it joins with the fascia that covers the inferior surface of the diaphragm. This aponeurosis is situated between the transversus abdominis muscle and the parietal peritoneum and has an opening at the deep inguinal ring through which the spermatic cord in males and the round ligament of the uterus in females passes. This fascia is continuous with the pelvic fascia and the iliac fascia.
The inferior wall of the inguinal canal acts as the floor of the canal and supports the inguinal structures. It contains the inguinal ligament, the lacunar ligament and the iliopubic tract. In this image, we can see the inguinal ligament here and the lacunar ligament here.
The inguinal ligament extends from the anterior superior iliac spine to the pubic tubercle. It is the lower edge of the external abdominal oblique aponeurosis and forms the base of the inguinal canal. It is clinically significant as it marks the superior border of the femoral triangle as well as the inferior border of the inguinal triangle. It is also an important structure to identify when operating on hernia patients.
The lacunar ligament is a connective tissue ligament that connects the inguinal ligament to the pectineal ligament. This ligament is a continuation of the external oblique muscle aponeurosis. It is clinically significant in that in the case of a femoral hernia, this ligament is the only boundary of the femoral canal that can be cut to release the hernia. In the next image, we can see this structure highlighted in green.
The last ligament we're going to look at is the pectineal ligament. It is sometimes referred to as the inguinal ligament of Cooper. This ligament is the continuation of the lacunar ligament and it runs along the pectineal line of the pubic bone. Again, in the next image, we can see the structure highlighted in green.
Next, let us look at the anterior border of the inguinal canal. The anterior border is covered by the aponeurosis of the external oblique muscle, the fleshy part of the internal oblique muscle and the superficial inguinal ring.
The last border we will look at is the posterior border. This formation is contributed by the transversalis fascia and the conjoint tendon. This border is made up of the inguinal falx, the reflected part of the inguinal ligament, and finally, the deep inguinal ring.
We will now move on briefly to discuss the major fasciae close to the inguinal region. First, let's begin by looking at the fascia found in the femoral region. The first fascia I'm going to discuss is the fascia lata which is a deep fascial investment of the whole thigh. In our illustration, you can see the portion of the fascia lata covering the upper part of the thigh; however, it actually covers a much larger area and receives fibers from the gluteus maximus. The tensor fascia lata can be found inserted between the layers of the fascia lata.
Next, we have the iliac fascia. This is found in the pelvic region and divides the area between the inguinal ligament and the hip bone into two compartments – a medial vascular lacuna compartment which transmits the femoral artery and vein and a muscular lacuna compartment which transmits the femoral nerve, psoas major and the iliacus muscle.
The contents of the inguinal canal can differ between the sexes. In both males and females, the contents of the inguinal canal include the blood vessels, lymphatic vessels and the inguinal nerve. In the male pelvis, the spermatic cord is contained in the inguinal canal and in the female pelvis, it's the round ligament of the uterus.
We've briefly mentioned the differences of the contents of the inguinal canal across to both sexes. We will now proceed further to describe the contents of the male inguinal canal – a set of delicate structures with high clinical relevance.
One of the contents of the male inguinal canal is the external spermatic fascia. The external spermatic fascia is a thin membrane that is derived from the aponeurosis of the external oblique muscle. It covers the spermatic cord and the testes. The spermatic cord – seen here highlighted in green – contains various structures within it including the vas deferens, the testicular, deferential, and cremasteric arteries, the genital branch of the genitofemoral nerve, the testicular nerves, the pampiniform plexus, the tunica vaginalis, and the lymphatic vessels.
The covering of the spermatic cord – as I mentioned previously – is made up of the external spermatic fascia as well as the cremasteric muscle and its fascia and the internal spermatic fascia. In the next image, we can see the spermatic cord and its contents highlighted in green. The vas deferens – also known as the ductus deferens – connect the epididymis to the ejaculatory duct. These two ducts transport the sperm to the ejaculatory ducts and a part of the spermatic cords. They're supplied by a similarly-named artery that accompanies the duct – the artery of vas deferens. In the next image, we can see the vas deferens highlighted in green contained within the spermatic cord.
Now that we've covered some of the structures found in the male inguinal canal, I just want to briefly show you this structure here which is the ureter. Be very careful not to confuse the spermatic cord with the ureter. The ureter is the excretory duct of the kidneys that connects the renal pelvis to the bladder. It is a retroperitoneal structure with no ties whatsoever to the inguinal region or canal. It is presented here simply to allow for a fuller understanding of spatial relationships with the inguinal region and to help avoid confusion.
Let's move on to discuss the arterial vessels of the thigh, pelvic and inguinal region. We will initially look at the major vessels then move on to the branches of these vessels directly related to the inguinal canal. The first artery that we will look at is the common iliac artery. The common iliac arteries are paired arteries that arise from the bifurcation of the abdominal aorta at the level of L4. They course inferolaterally along the medial border of the psoas major muscles and bifurcate in front of the sacroiliac joint giving the external iliac artery and the internal iliac artery. These two branches of the common iliac artery will be discussed briefly in the following slides.
So as I mentioned previously, the internal iliac artery arises from the bifurcation of the common iliac artery. It is the main artery of the pelvis. It gives off several branches that supply the walls and viscera of the pelvis. It gives off branches that supply the bladder, the reproductive organs and the medial compartment of the thigh. For more on the branches of the internal iliac artery, please check out the tutorials on the blood vessels of the female pelvis and the blood vessels of the male pelvis on our website.
The next branch of the common iliac artery that arises from its bifurcation in front of the sacroiliac joint is the external iliac artery. This artery – as you can see highlighted in green – travels inferiorly, anteriorly and laterally to the lower limb. The external iliac artery exits the pelvic girdle behind and inferior to the inguinal ligament and courses into the lower limb as the femoral artery. Aside from the femoral artery, the external iliac artery gives off two other branches that supply the muscles and skin of the lower abdominal wall. These are the inferior epigastric artery and the deep circumflex iliac artery.
The femoral artery is the main artery of the lower limb and, as I mentioned earlier, is a continuation of the external iliac artery extending from the inguinal ligament to the popliteal artery. In the next image, we can see the femoral artery within the femoral triangle. So, here is the femoral triangle and here we have the femoral artery, the femoral vein, and the femoral nerve. The deep femoral artery which is a branch of the femoral artery is the larger of the branches of the femoral artery and lies more deeply.
Another branch of the external iliac artery that we will discuss is the inferior epigastric artery. It arises from the external iliac artery immediately above and behind the inguinal ligament. It courses upward and passes between the rectus abdominis muscle and the posterior lamella of the muscle sheet. The inferior epigastric artery gives off numerous branches and also forms an anastomosis with the superior epigastric artery. This artery has a high clinical importance in hernia differential diagnosis. Hernias that arise medially to the inferior epigastric artery are classified as direct hernias while hernias protruding laterally from the artery are classified as indirect hernias.
The next artery we can see is the cremasteric artery that arises from the inferior epigastric artery. The cremasteric artery – as the name suggests – supplies blood to the cremaster muscle and the spermatic cord and forms an anastomosis with the testicular artery. In the female pelvis, this artery corresponds to the artery of the round ligament of the uterus. In the next image, we can see this structure in relation to the spermatic cord.
The next structure we are going to looking at is a paired artery of the male gonads and that's the testicular artery. As I just mentioned previously, the testicular artery anastomosis with the cremasteric artery. It arises from the abdominal aorta at approximately the level of the L2. These paired male gonadal arteries pass obliquely downward passing through the abdominal inguinal ring along with other contents of the spermatic cord through the inguinal canal and finally to the scrotum. These arteries supply blood to the testes and are innervated by post-ganglionic fibers from the celiac ganglion. This way they also provide sympathetic innervation to the testes.
The female gonadal arteries are the ovarian arteries which course differently to the testicular arteries due to the position of the ovaries in the female pelvis. Let's begin talking about the veins of the inguinal region by discussing the pampiniform plexus. The plexus refers to a rich network of interconnecting veins that surround the testicular artery within the spermatic cord. It is formed by the union of multiple veins arising from the back of the testes. As the plexus leaves the scrotum and enters the spermatic cord, its branches begin to coalesce until there are four branches. At the deep inguinal ring on either side of the testicular artery, a couple of branches fuse to form two valvular testicular veins. When the valves of the testicular veins malfunction, the plexus enlarges abnormally resulting in a condition known as a varicocele.
The testicular veins are paired male gonadal veins that carry deoxygenated blood from the pampiniform plexus to the inferior vena cava. They arise at the level of the deep inguinal ring as a venous pair surrounding the testicular artery on both sides of the body. Therefore, two valvular testicular veins travel alongside each testicular artery towards their drainage points. Shortly, thereafter, they combine into a single testicular vein traveling laterally to each testicular artery. It is important to know that the course of these veins differs on the right and left. The right testicular vein drains directly into the inferior vena cava while the left testicular vein drains into the left renal vein rather than draining directly into the inferior vena cava.
The femoral vein is a continuation of the popliteal vein and accompanies the femoral artery extending from the tendineus hiatus of the adductor canal to the inguinal ligament. It drains into the external iliac vein and receives tributaries from the popliteal vein, the deep femoral vein and the great saphenous vein. In the next image, we can see the femoral vein running parallel to the femoral artery.
Like the femoral vein, the inferior epigastric vein is also a tributary of the external iliac vein. It arises from the superior epigastric vein on the posterior side of the anterior abdominal wall and courses along with the inferior epigastric artery. The external iliac arteries are accompanied by the external iliac veins. As I mentioned previously, these two veins receive tributaries from the femoral vein and the inferior epigastric vein. They arise from the femoral veins at the inferior margin of the inguinal ligaments on the left and right side and join with the internal iliac veins to form the common iliac vein into which they drain.
The internal iliac vein which joins with the external iliac vein to form the common iliac vein persist upward from the upper part of the greater sciatic foramen accompanied by and running medial to the internal iliac artery. It receives tributaries from the veins of the pelvic viscera and the perineum. As already mentioned, the common iliac veins are formed by the joining of the external iliac vein and the internal iliac veins. The left and right common iliac veins form the inferior vena cava.
Next, let's move on to the innervation of the inguinal canal. The genitofemoral nerve which arises from the lumbar plexus L1 to L2 pierces the psoas major muscle and passes on top of it. This nerve gives off two branches – a genital branch and a femoral branch. The genital branch of the femoral nerve passes into the deep inguinal ring and through the inguinal canal. In females, the genital branch of the genitofemoral nerve accompanies the round ligament of the uterus and goes on to innervate the skin of the mons pubis and the labia majora.
In males, the genital branch of the genitofemoral nerve innervates the cremaster muscle, the internal spermatic fasciae, the tunica vaginalis as well as the skin of the scrotum. In males, the genital branch is also responsible for the cremasteric reflex which describes the contraction of the cremaster muscle elicited by the light stroking of the superior medial part of the thigh. The reflex is absent in most cases of testicular torsion.
The second branch of the genitofemoral nerve is the femoral branch. This branch passes underneath the inguinal ligament, courses between the femoral artery and the iliopectineal arch and, finally, through the saphenous hiatus to innervate the skin of the upper part of the anterior thigh. The femoral nerve which we can see in this next image is the largest branch of the lumbar plexus. It arises from the ventral rami of the lumbar nerves L2 to L4 and passes downwards through the fibers of the psoas major muscle. It courses further down between the iliacus and psoas major muscles and through the muscular lacuna. After it courses beneath the inguinal ligament, the nerve divides into an anterior and a posterior division.
The lateral femoral cutaneous nerve is a cutaneous nerve from the dorsal division of the lumbar plexus at L2 to L3. It innervates the skin of the lateral part of the thigh. It courses along the lateral margin of the psoas major beneath the iliac fascia and coursing beneath the inguinal ligament then through the lateral part of the muscular lacuna before passing over the sartorius major muscle to the lateral skin of the thigh.
The final structures of the inguinal region we will look at are the superficial inguinal lymph nodes. These lymph nodes are comprised of approximately ten lymph nodes and are situated in the femoral triangle of Scarpa. They form a chain immediately below the inguinal ligament and drain into the deep inguinal lymph nodes. The inguinal hernia is a very commonly occurring clinical condition and so before we finish this tutorial, I would like to share with you a couple of clinical notes.
An inguinal hernia is the protrusion or passage of a peritoneal sac, with or without abdominal contents, through a weakened part of the abdominal wall of the groin. It occurs because the peritoneal sac enters the inguinal canal either indirectly through the deep inguinal ring or directly through the posterior wall of the inguinal canal. Therefore, inguinal hernias are classed as either indirect or direct. The indirect inguinal hernia is the most common of the two types of hernias and is by far more common in men than in women. It occurs when part or all of the embryonic processus vaginalis remains open or patent. For this reason, it's considered as being congenital in origin. On the other hand, the direct inguinal hernia is usually described as acquired because it develops when abdominal musculature has been weakened and is commonly seen in older men.
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