Are you ready to knock out lymphatic drainage of the pelvis and perineum? Let's face it, lymphatic drainage is hard, and easy to ignore because of it, especially when it comes to lymphatic drainage of the pelvis and perineum. There's just so many nodes, and so many routes to get lost in. The purpose of this video is to simplify that pattern and then highlight a few exceptions to the rules. Let's start with the basics. All lymph from below the waist, including that from the lower limbs, abdomen, and pelvis, is ultimately drained by the thoracic duct. While lymph from above the waist drains via the right lymphatic duct or the thoracic duct depending on whether it's the right or left side of the body respectively. The thoracic duct returns lymph back into the venous system at the left venous angle. Otherwise said as, somewhere in the vicinity of where the subclavian vein and internal jugular vein join together to form the brachiocephalic vein. But how does lymph from the lower half of the body get to the thoracic duct? Three main trunks come together to form the cisterna chyli, which is a dilated sac that marks the beginning, or inferior end, of the thoracic duct. These three trunks include the right and left lumbar trunks, and the intestinal trunk. Lymph from the lower limbs, abdominal pelvic wall, and pelvic organs, drains via the lumbar trunks, while the intestinal trunk drains most abdominal organs. Now let's look specifically at drainage patterns of the pelvis and perineum. Most organs of the pelvis and perineum drain lymph into one of three nodes known as the external iliac nodes, internal iliac nodes, or the sacral nodes. Broadly speaking you can think of the drainage pattern in terms of stripy blocks being drawn across the organs. The external iliac nodes drain the superior portion of anterior organs including the superior bladder, as well as the body of the uterus in females. The inferior block is drained by the internal iliac nodes, which includes the inferior portion of the bladder, as well as the prostate and much of the erectile tissue of the penis in males, and a portion of the vagina in females. The internal iliac nodes also drain the superior two-thirds of the anal canal in both sexes. The sacral nodes drain a posterior block of organs including the inferior rectum in both sexes, as well as a portion of the vagina in females. Lymph from these three nodes (and remember we're talking about the internal iliac nodes, the external iliac nodes, and the sacral nodes) all drain into common iliac nodes, followed by lumbar nodes, and lastly into the lumbar trunks. The lumbar nodes are also known as para-aortic nodes as a result of their lateral placement to the aorta. An exception to this pattern however is worth noting. Lymph from the testes and ovaries, as well as the uterine tube, and fundus of the uterus, takes a direct route back to the lumbar nodes rather than wasting any time in the iliac nodes. This makes perfect sense when you consider it because the embryological origins of the gonads were within the abdomen. The gonads also retained their abdominal blood supply and as you know, lymph has a tendency to follow blood. Lymph from somatic areas of the perineum, such as the inferior one-third of the anal canal and superficial fascia inferior to the umbilicus, first follow a superficial route to the superficial inguinal lymph nodes. This is important to realize because these nodes are palpable and their enlargement may be an indication of cancer in any of the organs they drain. An additional organ that drains into these nodes that you might not think of is a portion of the uterus. Lymph from the lateral horns follows the round ligament of the uterus to drain into the superficial inguinal nodes. From these nodes, the lymph then drains deep, following the external iliac pathway back to the lumbar trunks. Lymph from the GI tract follows a unique pathway from that previously discussed. Lymph from this area follows its blood supply back to a cluster of three pre-aortic nodes that lie superficial to the aorta. This includes the celiac, superior mesenteric, and inferior mesenteric nodes. If we are considering organs within the pelvis, the sigmoid colon and superior rectum will follow this pathway. Specifically, lymph from these organs will drain to the inferior mesenteric nodes and from there into the intestinal trunk. The key thing to remember here is that there is much interconnectivity between pelvic nodes, so the lymphatic drainage, as well as metastatic cancer, can pass in any number of directions. Are you ready to test your knowledge? I'll call out an organ, or part of an organ, and you tell me the first node into which the lymph will drain out of four possible options. It's kind of like multiple choice; however, instead of calling out a b c or d, you'll be doing various exercises as your answers. You ready to do this? Let's go! Bladder Remember you are selecting the first node out of the four options into which lymph from that organ will first drain. Then do the exercise assigned to that node. Have you got your answer? And the correct answer is.... Do it a few more times just for good measure. Lower one third of the anal canal Remember the lower one-third of the anus is derived from somatic tissue, so this area drains to the superficial inguinal nodes. Testes Lymph follows blood supply, so lymph from the testes bypasses the iliac nodes and takes a straight shot back to the para-aortic or lumbar nodes. Scrotum Another somatic feature derived as an out pouching of the anterior abdominal wall. So, superficial inguinal nodes it is. Body and cervix of the uterus Lymph from the uterus drains via multiple different pathways, but the body and cervix primarily drain to the internal or external iliac nodes. Superior rectum Once again, lymph follows blood supply. This region is supplied by the inferior mesenteric artery, so the lymph follows that pathway back to the inferior mesenteric nodes, which are part of the pre-aortic nodes. Lateral horns of the uterus This is a strange one. Lymph from this area follows the round ligament of the uterus through the anterior abdominal wall to drain into the superficial inguinal nodes. That's it. I hope you've enjoyed this knockout review of lymphatic drainage of the pelvis and perineum.