Lymphatics of the abdomen and the pelvis
The lymphatic system is part of the circulatory system, and plays an important role in the immune system as well. It is comprised of a network of lymphatic vessels and nodes that collect and filter excess tissue fluid called lymph, before returning it to the venous circulation. This is done by the right lymphatic duct and the thoracic duct that empty lymph into the right subclavian vein and the left subclavian vein, respectively.
Lymph is a colorless fluid similar in composition to the blood plasma, but also contains white blood cells. The lymphatic vessels of the abdomen and pelvis can be divided into superficial and deep vessels. The superficial lymphatics originate from the subcutaneous tissue. They tend to accompany the venous flow, and ultimately drain into the deep vessels. The deep vessels on the other hand, drain deeper structures, like the internal organs. They tend to accompany the arteries.
The superficial lymphatics of the abdominal wall located above the umbilicus run in a superior direction towards the axillary lymph nodes. Those located below the umbilicus run in an inferior direction towards the superficial inguinal lymph nodes. The deep lymphatic drainage of the abdominal wall follows the deep arteries back to the parasternal lymph nodes along the internal thoracic artery, the lumbar lymph nodes along the abdominal aorta, and the external iliac lymph nodes along the external iliac artery.
The lymphatic drainage of the abdominal portion of the gastrointestinal tract, including the inferior part of the rectum, the spleen, the pancreas, the gallbladder, and the liver, is through vessels and lymph nodes that end in large collections of pre-aortic lymph nodes at the origins of the anterior branches of the abdominal aorta. According to their corresponding branches, these collections are termed the celiac, superior mesenteric, and inferior mesenteric groups of pre-aortic lymph nodes.
The lymphatic drainage of the deep structures and regions of the body below the diaphragm converges mostly on collections of lymph nodes and vessels related to the major blood vessels of the posterior abdominal region. The lymph then proceeds to drain into the thoracic duct. The pre-aortic lymph nodes anterior to the abdominal aorta, together with the right and left lateral aortic or lumbar lymph nodes (para-aortic lymph nodes), pass through the posterior abdominal region and collect lymph from several structures. The lateral aortic or lumbar lymph nodes receive lymphatics from the body wall, the kidneys, the suprarenal glands, and the testes or ovaries.
Lymphatics from the pelvic region and viscera drain mainly into the lymph nodes distributed along the internal and external iliac arteries and their branches. They then drain into the lymph nodes related to the common iliac arteries, which drain into the lateral aortic or lumbar lymph nodes. These lymph nodes then drain into the lumbar trunks which continue over to the thoracic duct.
The lymphatics from the deep part of the perineum accompany the internal pudendal blood vessels and drain into the internal iliac lymph nodes present in the pelvis. The lymphatic vessels of the superficial tissue of the penis or clitoris run along with the superficial external pudendal blood vessels, and mainly drain into the superficial inguinal lymph nodes, just like the lymphatic vessels of the scrotum or labia majora. The glans penis, glans clitoris, labia minora, and the terminal inferior end of the vagina, all drain into the deep inguinal and external iliac lymph nodes.