Lymphatic vessels
Lymph leaves the lower limb through two sets of vessels: a superficial set in the subcutaneous tissue, which carries most of the lymph, and a deep set beneath the deep fascia.
Superficial vessels
The superficial vessels begin as a fine plexus in the skin of the sole and dorsum of the foot and run upward with the superficial veins.
- Medial group: the larger group. These vessels accompany the great saphenous vein up the medial leg and thigh and end in the vertical group of superficial inguinal nodes. Many vessels from the lateral side of the foot and front of the leg cross over to join this group.
- Lateral group: vessels from the lateral border of the foot and the posterolateral calf follow the small saphenous vein, pierce the deep fascia of the popliteal fossa and end in the popliteal nodes.
Deep vessels
The deep vessels drain muscles, bones and joints. They run with the deep veins: those of the leg follow the anterior and posterior tibial and fibular vessels to the popliteal nodes, and those of the thigh follow the femoral vessels to the deep inguinal nodes. Deep lymphatics of the gluteal region follow the superior and inferior gluteal vessels to the internal iliac nodes, bypassing the groin.
Lymph vessels contain numerous valves. Flow up the limb depends on the contraction of the vessel walls, the calf muscle pump and movement of the limb, so lymph pools in an immobile, dependent leg.
Lymph nodes
The lymph nodes of the lower limb form three groups: the superficial inguinal, deep inguinal and popliteal nodes.
| Group | Location | Receives from | Drains to |
|---|---|---|---|
| Superficial inguinal nodes | Subcutaneous tissue of the upper thigh. Horizontal group just below and parallel to the inguinal ligament; vertical group along the end of the great saphenous vein | Superficial tissues of the limb (vertical group); lower anterior abdominal wall, buttock, perineum, external genitalia and lower anal canal (horizontal group) | Deep inguinal and external iliac nodes, through the saphenous opening |
| Deep inguinal nodes | Medial to the femoral vein under the fascia lata; the highest often in the femoral canal | Superficial inguinal nodes, deep vessels of the thigh, popliteal nodes, glans penis or clitoris | External iliac nodes, through the femoral canal |
| Popliteal nodes | Popliteal fat; one near the termination of the small saphenous vein, others around the popliteal vessels | Lateral foot and posterolateral calf via the small saphenous vessels; deep leg vessels; knee joint | Deep inguinal nodes, along the femoral vessels |
From the external iliac nodes, lymph passes to the common iliac and then the lumbar (lateral aortic) nodes. The lumbar trunks carry it to the cisterna chyli and on through the thoracic duct, which empties into the left venous angle at the junction of the left internal jugular and subclavian veins.
Drainage territories
Knowing which skin drains to the groin is the key clinical skill, because an enlarged inguinal node may come from anywhere in that territory.
- Superficial inguinal nodes drain the skin of almost the entire lower limb, the buttock, the anterior abdominal wall below the umbilicus, the perineum, the scrotum and skin of the penis or the vulva, the lower vagina, and the anal canal below the pectinate line. A small amount of lymph from the uterine fundus reaches them along the round ligament.
- Popliteal nodes are the first station only for the lateral foot, heel and posterolateral calf, and for the deep structures of the leg.
- Not the groin: the testis drains to the lumbar (para-aortic) nodes, following its vessels back to their origin at the level of L1 and L2, even though the scrotum around it drains to the superficial inguinal nodes.
Clinical relevance
The lymphatics of the lower limb matter clinically for the spread of cancer and infection and for lymphoedema.
Inguinal lymphadenopathy
Enlarged inguinal nodes demand examination of the whole territory: the foot and leg, the buttock, the perineum, the anal margin, the external genitalia and the lower abdominal wall. Small, soft, mobile nodes are common in healthy adults, particularly those who walk barefoot. A lump medial to the femoral vein below the inguinal ligament may be a deep inguinal node or a femoral hernia.
Cancer
Melanoma of the leg, and squamous cell carcinoma of the vulva, penis and anal margin, spread first to the inguinal nodes. Sentinel lymph node biopsy maps the first draining node with dye and radioisotope; a node positive for cancer may lead to inguinal or ilioinguinal node dissection. Lymphocele and wound breakdown are common after groin dissection because the area is rich in lymph vessels.
Infection
Cellulitis of the foot or leg can spread as lymphangitis, visible as red streaks running up the medial leg and thigh towards tender inguinal nodes.
Lymphoedema
Lymphoedema is swelling from failure of lymph drainage.
- Primary: developmental abnormalities of the lymphatics, presenting at birth (for example Milroy disease), around puberty or later in adult life.
- Secondary: filariasis, the commonest cause worldwide; in the UK, cancer treatment with inguinal or pelvic node dissection and radiotherapy, recurrent cellulitis, obesity and chronic venous disease.
The swelling starts distally, involves the toes and the dorsum of the foot, and the skin at the base of the second toe cannot be pinched up (Stemmer's sign).