The neurovascular structures of the pelvis include nerves, arteries, veins, and lymph nodes. These structures lie on the posterolateral walls of the pelvic cavity.
Generally the somatic nerves are the most lateral, arteries lie medial to nerves, and veins lie between these two.
Lymph nodes are usually clustered around the veins, and lymph vessels that come off these nodes ascend parallel to the veins. Now, let's take a closer look at the lymphatics and nerves of the pelvis specifically.
Let’s talk about the lymphatic drainage of the pelvis, which follows various major and minor groups of lymph nodes.
These lymph nodes have variable, sizes, numbers, and locations, and the lymph node clusters’ names are based on the adjacent structures and nearby blood supply.
Furthermore, these nodes are all interconnected, so their drainage often overlaps and can vary quite a bit.
First, there are the inguinal lymph nodes which lie around the inguinal ligament, and they’re divided into superficial and deep inguinal lymph nodes.
The superficial inguinal lymph nodes receive lymphatic drainage from the superficial lower limb, abdominal wall inferior to the umbilicus, gluteal region and superficial perineal structures such as the distal vagina, vulva and scrotum, and typically drain into the external iliac lymph nodes.
The deep inguinal lymph nodes receive lymph from the superficial inguinal nodes, as well as the deep portions of the lower limb, the glans clitoris in females or glans penis in males and the distal spongy urethra. These nodes typically drain into the external and common iliac lymph nodes.
Now, in addition to the inguinal lymph nodes, the external iliac lymph nodes also receive lymph from the anterior superior pelvic viscera, such as the body of the uterus, anterior cervix, and superior bladder.
Finally, the external iliac lymph nodes drain lymph into the common iliac lymph nodes, which lie around the common iliac artery
Next are the internal iliac lymph nodes, which lie along the anterior and posterior divisions of the internal iliac artery.
They drain lymph from inferior pelvic viscera and deep perineal structures such as the prostate, cervix, and proximal vagina.
Then, the internal iliac lymph nodes drain into the common iliac lymph nodes, just like the external iliac lymph nodes.
Next are the sacral lymph nodes, which lie in the concavity of the sacrum, near the median sacral blood vessels.
These lymph nodes receive lymph from the more posterior and inferior pelvic structures such as the inferior rectum and vagina. Then, they drain into the internal iliac lymph nodes or the common iliac lymph nodes.
Finally, there are the common iliac lymph nodes, which lie along the common iliac blood vessels. These lymph nodes receive lymph from the external iliac, internal iliac, and sacral lymph nodes.
Part of some pelvic viscera, like the neck of the urinary bladder and the inferior part of the vagina, may bypass their other sets of nodes and drain their lymph directly into the common iliac lymph nodes.
From the common iliac lymph nodes, lymph goes to the lumbar lymph nodes, which are also called caval or aortic lymph nodes.
The aortic lymph nodes also drain lymph directly from the testes and ovaries, and the fundus of the uterus.
Before wrapping up the pelvic lymph nodes, it’s worth mentioning a minor group of lymph nodes called pararectal lymph nodes.
These lymph nodes lie in the connective tissue that surrounds branches of the internal iliac blood vessels.
Alright, before we look at pelvic nerves, feel free to pause the video and see if you can name the main lymph node groups of the pelvis!
Okay, now, let’s switch gears and look at the nerves of the pelvis, which can be divided in somatic and autonomic nerves.
Somatic nerves arise from the lumbosacral and coccygeal plexus. These include the obturator nerve, the lumbosacral trunk, and spinal nerves that arise from the sacral and coccygeal segments of the spinal cord.
Sacral and coccygeal spinal nerves interconnect to form an extensive network of nerves called the sacral and coccygeal nerve plexuses, which lie on the piriformis and coccygeus muscles.
Let’s start with the obturator nerve, which arises from the lumbar plexus - specifically, the anterior rami of the second, third, and fourth lumbar spinal nerves.
This nerve enters the lesser pelvis and runs along the lateral wall of the pelvis to the obturator canal, which is an opening within the obturator membrane.
After entering the obturator canal, the obturator nerve divides into anterior and posterior branches, which actually don’t supply any structures within the pelvis. Instead, these branches enter the thigh and supply the adductor muscles of the medial thigh.
Now, right above the pelvic brim, the descending part of the fourth lumbar nerve unites with the anterior ramus of the fifth lumbar nerve, forming the lumbosacral trunk.
This trunk descends on the anterior surface of the ala of the sacrum, and it unites with the sacral plexus, forming the lumbosacral plexus.
So the lumbosacral plexus is formed by the anterior rami of spinal nerves L4 to S4. This plexus lies on the posterolateral wall of the lesser pelvis, and it gives off a number of branches for pelvic and lower limb structures.
The first of these branches is the sciatic nerve, which is the largest nerve of the human body. This nerve arises from the anterior rami of spinal nerves L4 to S3.
Then, it passes through the greater sciatic foramen, typically below the piriformis muscle, and enters the gluteal region.
Finally, it descends on the posterior aspect of the thigh and gives branches that supply the hip joint, posterior muscles of the thigh, and all the muscles of the leg and foot.
Second, there’s the pudendal nerve, which arises from spinal nerves S2, S3 and S4. After it forms, the pudendal nerve leaves the pelvis through the greater sciatic foramen, between the piriformis and coccygeus muscles.
Then, it winds around the ischial spine and the sacrospinous ligament. Finally, it passes through the lesser sciatic foramen and enters the perineum to provide sensory information to the external genitalia as well muscular branches to perineal muscles.
Two other branches of the lumbosacral plexus are the superior gluteal and inferior gluteal nerves. The superior gluteal nerve arises from L4, L5, and S1.
This nerve leaves the pelvis above the piriformis muscle, and it passes through the greater sciatic foramen to supply the gluteus medius and gluteus minimus muscles in the gluteal region.
Finally, the inferior gluteal nerve, which arises from L5, S1, and S2. This nerve also leaves the pelvis through the greater sciatic foramen, but below the piriformis muscle.
The inferior gluteal nerve supplies the gluteus maximus, which is the largest muscle of the gluteal region and, in fact, the entire body!
Here’s a memory trick! The relations of these nerves to the piriformis muscle correspond to their names.
The superior gluteal nerve passes above the piriformis, and the inferior gluteal nerve passes below the piriformis.