Lymphatics of the Retroperitoneal Space
The abdominal cavity contains the largest portion of our digestive tract in addition to the internal component of our renal system. The lymphatic system responsible for draining these organs, as well as the abdominal musculature, of lymph is found not only adjacent to the individual organs, but also in the retroperitoneal space.
These retroperitoneal nodes and vessels are responsible for draining the lymph from the abdominopelvic gastrointestinal system as well as the deep tissue of the retroperitoneal space. More specifically, it receives tributaries with lymph from the skin, muscles and deep tissues of the posterior abdominal wall. This article will focus on the anatomical locations of these lymph nodes and vessels. Additionally, it will also look at clinically significant points relative to this segment of the lymphatic pathway.
Para-aortic Lymph Nodes
The retroperitoneal space is defined as the area of the abdominal cavity that is posterior to the parietal peritoneum and anterior to the anterior fascia of the posterior abdominal wall (fascia of quadratus lumborum). The lymph nodes of this cavity are closely associated with the abdominal aorta and its branches. The nodes are therefore referred to as the para-aortic group of lymph nodes. They can be further subdivided into pre-aortic, coeliac, mesenteric, lateral aortic and retro-aortic groups of lymph nodes.
Pre-aortic Lymph Nodes
- superior mesenteric and
- inferior mesenteric nodes,
Mesenteric Lymph NodesThe mesenteric nodes are the most caudal of the pre-aortic lymph nodes. They are further subdivided into the superior and inferior mesenteric nodes. The afferents to the superior mesenteric nodes arise from the mesenteric nodes (found between the layers of the mesentery), ileocolic nodes (found along the ileocolic artery and its branches) and the mesocolic nodes (within the mesocolon along the transverse colon). The similarities between these nodes and their associated arteries are uncanny. The superior mesenteric nodes are responsible for lymph drainage of the midgut (i.e. from the duodenojejunal flexure to the watershed area of the transverse colon).
Likewise, the inferior mesenteric nodes receive lymph from the same areas supplied by the artery for which it was named (i.e. the distal third of the transverse colon, descending colon, sigmoid colon and proximal rectum). This cluster of nodes include smaller groups associated with the sigmoid and left colic arteries, another cluster surrounding the superior hemorrhoidal artery and sigmoid mesocolon and a final pararectal cluster that is found next to the rectum. The inferior mesenteric nodes will drain to the superior mesenteric nodes, which then send efferent lymph vessels to the coeliac nodes.
Coeliac Lymph Nodes
The coeliac trunk, or coeliac axis, is the first and largest branch from the anterior surface of the abdominal aorta. The artery subsequently trifurcates into the left gastric, common hepatic and pancreaticosplenic arteries. Surrounding this large artery and its branches are the coeliac nodes. They are the terminal nodes of the pre-aortic and regional lymph nodes (those associated with the branches of the artery). The gastric nodes (surrounding the left gastric artery) drain lymph from the abdominal oesophagus, stomach, proximal duodenum and greater omentum. Hepatic nodes are those surrounding the hepatic arteries and biliary tree. They receive lymph from the liver, gallbladder and biliary tree. Finally, the pancreaticosplenic group of nodes drain the pancreas, spleen and a portion of the stomach.
Intestinal Lymph Trunks
The coeliac group of nodes give rise to the intestinal lymph trunk. In addition to receiving afferents directly from the coeliac nodes, it also receives lymph indirectly from the superior and inferior mesenteric nodes and their tributaries. This trunk forms part of the lymph channels in the retroperitoneum that is responsible for draining the abdominopelvic components of the gastrointestinal system.
Lateral Aortic Nodes
Anterior to the diaphragmatic crura, sympathetic trunk and medial borders of the psoas major muscle are the lateral aortic (para-aortic) lymph nodes. While these nodes are rarely found between the inferior vena cava and abdominal aorta, they can be seen anterolateral to the inferior vena cava at the distal end of the right renal vein. Tributaries to these nodes include structures that are perfused by the dorsal and lateral branches of the abdominal aorta. These include the kidneys and adrenal (suprarenal) glands, ureters, as well as the gonads, uterine tubes and cranial portion of the uterus (in females). The deep tissues of the posterior abdominal wall also drain to this group.
Lumbar Lymph Trunks
Efferent vessels of the lateral aortic node will coalesce and form the left and right lumbar lymph trunks. In addition to draining the tributaries of the lateral aortic nodes (named above) the lumbar trunks will also carry lymph from the perineal wall, pelvic wall and the region of the anterior abdominal walls caudal to the umbilicus as well as most of the deep tissue of the anterior abdominal wall cranial to the umbilicus.
The left and right branches of the lumbar lymph trunks converge anterolateral to the L1-L2 vertebrae to form the cisterna chyli. This is an approximately 5 – 7 cm long sac-like, fusiform dilatation that receives lymph from the major abdominal trunks. The cisterna chyli or confluence of lymph trunks extends cranially to the right of the abdominal aorta to form the abdominal part of the thoracic duct at the level of T12 or the thoracolumbar intervertebral disc.
The right lumbar azygous vein and two cranial lumbar arteries are medially related to the cisterna chyli, while the medial border of the right diaphragmatic crus is anteriorly related to the structure. While most of the lymph that passes through the cisterna chyli is delivered by the lumbar and intestinal trunks, it also receives direct tributaries from the right group of pre-aortic nodes (namely the right lateral aortic, coeliac and superior mesenteric nodes).
Retro-aortic Lymph Nodes
The retro-aortic lymph nodes is the smallest group of para-aortic nodes. While there isn’t a defined set of areas that drain to this set of nodes, it occasionally receives tributaries from the paraspinal posterior abdominal wall. Otherwise, it functions as intermediary group that drains to the lateral aortic nodes.
The abdominal lymph trunks along with the cisterna chyli are large vessels that carry a large volume of lymph. This makes it particularly difficult for them to automatically seal following trauma. Consequently, surgical procedures may be complicated by this factor owing to the close relationship between the lymphatic trunks and the abdominal aorta. Iatrogenic injury of this nature may give rise to a chylous ascites (i.e. ascites secondary to lymph extravasation). It should be noted, however, that this is a rare condition that has several aetiologies.
The retroperitoneal lymph nodes receive lymph from the lower limbs, genitals, pelvic viscera and retroperitoneal structures (including, but not limited to, the suprarenal glands, ureters, ascending and descending colon, kidneys and oesophagus). Tumor metastasis to these nodes from the afore-mentioned sites is not uncommon. In some cases of testicular carcinoma, renal cell carcinoma and upper urinary tract urothelial carcinoma and other urologic malignancies, a procedure known as retroperitoneal lymph node dissection can be conducted as both a diagnostic and therapeutic procedure.