Lymphatic Vessels and Nodes of the Pelvis
The lymphatic vessels and nodes of the pelvis return lymph from pelvic organs, and follow a certain course that generally, but not reliably, follow the pattern of venous drainage of the pelvic structures. Lymphatic capillaries with fenestrated endothelial cell lining are blind ended tubes, they merge into lymphatic vessels which possess valves and contain muscles in their walls. These lymphatics drain into lymph nodes, the lymph nodes are present in the form of chain or rows. The final destination of lymph is into thoracic duct and subclavian vein.
Unlike the other organs, the pelvic organs do not have hilum so they are supplied and drained into both sides of pelvis. Pelvic organs are mostly suspended by dense connective tissue suspensory apparatus which carry blood vessels, nerves and lymphatics to these organs. Several groups of lymph nodes have been identified in pelvis and mainly include the sacral, internal, external, and common iliac lymph nodes. There are few minor groups of lymph nodes like pararectal nodes in the connective tissue along the branches of internal iliac vessels. The pelvic lymph nodes receive afferent from pelvic, peripheral, visceral and parietal structures and send efferents to proximal group of lymph nodes.
Lymph Nodes of the Pelvis
The location and number of several groups and sub-groups of lymph nodes receiving lymph drainage from the pelvic organs vary but four main groups are well known and can be described as follows:
- External iliac nodes: These group of lymph nodes are located above the pelvic brim, along the external iliac vessels. Apart from receiving lymph directly from pelvic structures, especially the superior parts of the middle to anterior pelvic organs, they also receive lymph from the inguinal lymph nodes. These inguinal lymph nodes are the main structures they drain. The external iliac nodes return lymph into the common iliac nodes.
- Internal iliac lymph nodes: These nodes derive their name from the internal iliac vessel. They form a cluster around the anterior and posterior divisions of the internal iliac artery and the origins of the gluteal arteries. They receive drainage from the inferior pelvic viscera, deep perineum, and gluteal region and like the external iliac nodes, drain into the common iliac nodes.
- Sacral lymph nodes: Within the pelvis, at the concavity of the sacrum, lies the sacral group of lymph nodes. They receive lymphatic vessels which course along the median sacral blood vessels. Specifically, they receive lymph from the posteroinferior pelvic viscera and drain either to internal or common iliac group of lymph nodes.
- Common iliac lymph nodes: The common iliac lymph nodes mainly drain other lymph nodes within the pelvis. They are located above the pelvis and receive drainage from the sacral, external iliac and internal iliac groups of lymph nodes. They mainly drain lymph into the caval and aortic groups of lymph nodes. Some direct lymph drainage into the common iliac nodes occurs from some pelvic organs, for example, the direct lymphatic vessels from the neck of the urinary bladder and the inferior parts of the vagina. Depending upon their location this group of lymph nodes is divided into three sub-groups:
- Lateral: direct continuation of external iliac lymph nodes
- Posterior: receives lymph from external and internal iliac nodes
- Medial: lies below the aortic bifurcation and receives lymph from internal iliac nodes
In females, lymphatic drainage from the ovaries and uterine tubes follow the ovarian veins to the lumbar lymph nodes (i.e., the caval and aortic lymph nodes). Furthermore, the lymphatic drainage of the testis and epididymis also drain to those lumbar nodes, even though these structures are located outside the pelvis. These nodes are composed of right and left lateral aortic chains, preaortic and retroaortic chains. Lateral receives drainage from common iliac and sacral nodes and also from ovary and testis. Preaortic receives lymph from rectum, anal canal, colon and anterior abdominal wall while retroaortic receives drainage from posterior abdominal wall.
Such sub-groups of lymph nodes, as well as the main groups like those of the pelvis described above, are usually highly interconnected to allow free flow of drainage. However, in some clinical conditions like cancer affecting one organ, there can be a spread to other regions through the interconnecting lymphatic network.