Anatomy of the inguinal region

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Introduction0:00–0:32

The inguinal region, sometimes called the groin, is the lower part of the anterolateral abdominal wall. It’s a small area of great importance, as it serves as a passageway for structures such as the spermatic cord, vessels, and nerves to enter or leave the abdominal cavity.The inguinal region is a compact space, located superior to the thigh, lateral to the pubic tubercle, and inferomedial to the anterior superior iliac spine.

Inguinal ligament0:32–1:33

One important structure in this region is the inguinal ligament, which is a thick fibrous band formed by the inferior border of the external oblique aponeurosis.
The inguinal ligament extends from the anterior superior iliac spine of the ilium, to the pubic tubercle on the pubic bone.
Medially, the inguinal ligament’s attachment to the pubis is reinforced by a number of smaller fibrous extensions, including the lacunar ligament and the pectineal ligament.
The lacunar ligament attaches along the superior pubic ramus and some fibres continue along the pecten pubis as the pectineal ligament.
The lacunar ligament forms the medial border of the subinguinal space, located inferior to the inguinal ligament. Important structures that pass through this space include the psoas major and iliacus muscles and also the femoral nerve, artery and vein, and the lateral cutaneous nerve of the thigh.
Now, the most important feature of the inguinal region is the inguinal canal, which is a passage that extends inferomedially through the anterolateral abdominal wall.

Inguinal canal1:33–4:49

To better understand the anatomy of this canal, let’s look at how it develops!In genetically male individuals, the testes begin to develop in the extraperitoneal space of the posterior abdominal wall, and within the first few months each testis descends into the pelvis, pulled by a structure called the gubernaculum, which attaches to the anterolateral abdominal wall - and, later, to the developing scrotum.
As the testis descends from the abdominal cavity into the scrotum, its vessels and nerves migrate with it. When the testis gets closer to the anterolateral abdominal wall, a peritoneal outpouching called the processus vaginalis forms, and pulls the layers of the anterolateral abdominal wall with it into the developing scrotum.
The testis then follows the processus vaginalis into the scrotum. In males, the inguinal canal contains the ilioinguinal nerve and the spermatic cord, which includes the genital branch of the genitofemoral nerve.
In genetically female individuals, the development of the inguinal canal is slightly different. While the ovaries also begin their development in the abdomen, they only descend as far as the pelvis.
Because of this, the inguinal canal is less developed compared to males and obviously doesn’t contain a spermatic cord. However, the inguinal canal in females contains the ilioinguinal nerve, the genital branch of the genitofemoral nerve, and the round ligament of the uterus, which is a remnant of the gubernaculum that extends from each ovary to the labia majora.Alright, now, the inguinal canal starts at the deep inguinal ring, which is an opening in the transversalis fascia and is located at the midpoint of the inguinal ligament, just lateral to the inferior epigastric vessels.
The inguinal canal ends at the superficial inguinal ring, which is an opening in the external oblique aponeurosis. Structures passing through the inguinal canal enter through the deep inguinal ring - except the ilioinguinal nerve, which enters the canal distal to the ring - and they all exit through the superficial inguinal ring.Now, the inguinal canal has four boundaries, which include the anterior and posterior walls, the roof, and the floor.
The anterior wall is made up of the external oblique aponeurosis, while the posterior wall is formed by the transversalis fascia, and is reinforced medially by the conjoint tendon, which is the union of the transversus abdominis and internal oblique aponeuroses.
The roof is formed by different elements along the canal. Laterally, the roof of the inguinal canal is formed by the transversalis fascia, centrally by musculoaponeurotic arches of the internal oblique and transversus abdominis, and medially, by the medial crus of the external oblique aponeurosis.
Finally, the floor of the inguinal canal consists primarily of the gutter formed by the inguinal ligament, and is supported medially by the lacunar ligament.Alright, now feel free to pause the video and see if you can recall what structures pass through the inguinal canal in males!Alright, now let’s have a look at the spermatic cord itself, which suspends each testis in the scrotum.

Quiz4:49–5:01

Spermatic cord5:01–6:43

Including its fascial coverings, the spermatic cord contains twelve structures, which can be put into four groups of three.
So we can use the 3 3 3 3 rule to help remember them! The first group is the fascial layers of the spermatic cord.
From deep to superficial, the layers are: the internal spermatic fascia derived from the transversalis fascia, the cremasteric fascia derived from the internal oblique muscle, and the external spermatic fascia derived from the aponeurosis and deep fascia of the external oblique muscle.
Next up, are the 3 arteries, namely the artery to vas deferens, the testicular artery, and the cremasteric artery. Then, there are the 3 nerves, which are the genital branch of the genitofemoral nerve, sympathetic fibers, and visceral afferent fibers.
Finally, there are 3 other structures; the pampiniform venous plexus, the vas deferens, and the testicular lymphatic vessels.
Now let’s briefly look at the cremasteric fascia and muscle. The cremasteric fascia contains fibers of the cremaster muscle, which is derived from the lower fascicles of the internal oblique muscle that arise from the inguinal ligament and it extends inferiorly to form a covering of the spermatic cord and testis.
The cremaster muscle is innervated by the genital branch of the genitofemoral nerve, and its contraction helps retract the testis - or draw it superiorly - to regulate its temperature for optimal sperm production.Let’s have another pause, and see if you can remember the contents of the spermatic cord.

Quiz6:43–6:56

Now, let’s make our way down to the scrotum, which is made up of two main layers: the skin; and the dartos fascia.The dartos fascia is continuous anteriorly with the subcutaneous tissue of the abdomen called the Scarpa fascia, and posteriorly with the subcutaneous tissue of the perineum, or Colles fascia.

Scrotum6:56–7:43

Now, the dartos fascia contains smooth muscle - called the dartos muscle - and it’s attached to the scrotal skin. So when the muscle contracts, the skin moves with it, causing the scrotum to wrinkle when it’s cold.
It also helps retract the testis. Both of these functions limit heat loss.
The dartos muscle is innervated by sympathetic fibers of the genital branch of the genitofemoral nerve.Now let’s look within the scrotum at the testes and their coverings.

Testis7:43–9:58

Each testis is partially covered by a layer of the peritoneal membrane, called the tunica vaginalis, which is a serous membrane covering the testis.
In fact, it’s the embryological remnant of the processus vaginalis! The visceral layer of the tunica vaginalis covers the testis except for the part where the testis is attached to the epididymis and spermatic cord.
The visceral layer of the tunica vaginalis continues as the parietal layer, which lies adjacent to the internal spermatic fascia.
On their outer part, the testes have a tough fibrous capsule called the tunica albuginea, which is made up of dense connective fibrous tissue that continues inside the testes, creating septa that divide them into lobules.
These lobules contain the coiled seminiferous tubules, which is where sperm are produced. The sperm travel from the seminiferous tubules into the straight tubules and then into the rete testis, which is a network of collecting canals.
From here, the sperm move to the epididymis through efferent ductules. The epididymis has 3 parts, the head, where the efferent ductules merge; the body; and the tail, which continues as the vas deferens.
Each one of the two testes is supplied by a testicular artery, which is a direct branch of the abdominal aorta, emerging just inferior to the renal artery.
Their venous drainage is through a network of veins called the pampiniform plexus, which drains into the right or left testicular vein.
The right testicular vein drains into the inferior vena cava directly, whereas the left testicular vein drains into the left renal vein.
The lymphatic drainage of the testes is to the preaortic and lateral aortic lymph nodes. In contrast, the scrotum’s lymphatic drainage is to the nearby superficial inguinal lymph nodes.Remember, the testes develop in the abdomen and eventually descend, so it makes sense their lymphatic drainage is to lymph nodes in the abdomen, not to the inguinal lymph nodes.

Review9:58–11:54

Alright, as a quick recap. The inguinal ligament extends from the anterior superior iliac spine of the ilium to the pubic tubercle on the pubic bone.
The inguinal canal has a deep ring, located just lateral to the inferior epigastric artery, and a superficial ring. The inguinal canal has four boundaries, which are the anterior wall consisting of the external oblique aponeurosis, the posterior wall consisting of the transversalis fascia, the roof formed by internal oblique and transversus abdominis muscles; and finally, the floor, which consists of the inguinal and lacunar ligaments.
In both genetically male and female individuals, the inguinal canal transmits the ilioinguinal nerve and genital branch of the genitofemoral nerve.
In males, the inguinal canal also transmits the spermatic cord, while in females, it contains the round ligament of the uterus.
The male’s spermatic cord consists of 3 layers, which are internal spermatic fascia, the cremasteric fascia, and the external spermatic fascia.
It carries 3 arteries, which are the artery to vas deferens, the testicular artery, and the cremasteric artery; 3 nerves, namely the genital branch of the genitofemoral nerve, sympathetic fibers, and visceral afferent fibers and finally, 3 other structures, which are the pampiniform venous plexus, the vas deferens, and the testicular lymphatics.
The testes reside in the scrotum and are directly covered by the visceral layer of the tunica vaginalis, which is continuous with the parietal layer of the tunica vaginalis.
They are supplied by testicular arteries, which are direct branches of the abdominal aorta. Their venous drainage is through the pampiniform plexuses, while the lymphatic drainage is to the preaortic and lateral