The lymphatic system functions to drain tissue fluid, plasma proteins and other cellular debris back into the blood stream, and is also involved in immune defence. Once this collection of substances enters the lymphatic vessels it is known as lymph; lymph is subsequently filtered by lymph nodes and directed into the venous system.
This article will explore the anatomy of lymphatic drainage throughout the lower limb, and how this is relevant clinically.
The lymphatic vessels of the lower limb can be divided into two major groups; superficial vessels and deep vessels. Their distribution is similar to the veins of the lower limb.
Superficial Lymphatic Vessels
The superficial vessels can be divided into two major subsets; (i) medial vessels, which closely follow the course of the great saphenous vein and; (ii) lateral vessels which are more closely associated with the small saphenous vein.
The medial group originate on the dorsal surface of the foot. They travel up the anterior and posterior aspects of the medial lower leg, with the great saphenous vein, passing with it behind the medial condyle of the femur. This group of vessels ends in the groin, draining into the sub inguinal group of the inguinal lymph nodes.
The lateral vessels arise from the lateral surface of the foot and either accompany the small saphenous vein to enter the popliteal nodes, or ascend in front of the leg and cross just below the knee joint to join the medial group.
Deep Lymphatic Vessels
These are far fewer in number than their superficial counterparts and accompany the deep arteries of the lower leg. They are found in 3 main groups: anterior tibial, posterior tibial and peroneal following the corresponding artery respectively, and entering the popliteal lymph nodes.
The inguinal nodes are found in the upper aspect of the femoral triangle and are 1—20 in number.
They are subdivided into 2 groupings determined by their position relative to a horizontal line drawn at the level of termination of the great saphenous vein. Those below this line are the sub-inguinal nodes (consisting of a deep and superficial set) and those above are the superficial inguinal nodes.
Superficial Inguinal Nodes
These form a line directly below the inguinal ligament and receive lymph from the penis, scrotum, perineum, buttock and abdominal wall.
Superficial Sub-Inguinal Nodes
These are located on each side of the proximal section of the great saphenous vein. They receive afferent input primarily from the superficial lymphatic vessels of the lower leg.
Deep Sub-Inguinal Nodes
These are often found in one to three in number and are most commonly found on the medial aspect of the femoral vein. The afferent supply to these nodes is from the deep lymphatic trunks of the thigh which accompany the femoral vessels.
The popliteal lymphatic nodes are small in size, usually between five and seven in number, and are often found imbedded in fat reserves in the popliteal fossa. They receive lymph from the lateral superficial vessels.
The efferent vessels of the popliteal nodes pass almost entirely alongside the femoral vessels to empty into the deep inguinal nodes. However, some will accompany the great saphenous vein and drain into the sub-inguinal nodes.
Clinical Relevance: Lymphadenopathy
Lymphadenopathy is characterised by an abnormality in size, number or consistency of any lymphatic nodes within the body. This is usually in response to infection, malignancy or an auto-immune condition.
Abnormality of the inguinal vessels should always be viewed suspiciously. The superficial inguinal nodes receive drainage from the penis, scrotum, buttocks and abdominal wall as far as the umbilicus. Suspicion of lower limb lymphadenopathy therefore should include a full examination of both the lower limb and these structures.
In males, the testicles follow a different lymphatic route, and drain directly to the para-aortic nodes and therefore will rarely cause inguinal lymph node enlargement.