Lymphatic drainage

The thoracic duct drains everything below the diaphragm plus the left half of the head and neck, the left upper limb and the left thorax, which is about three-quarters of the body, and ends at the left venous angle. The right lymphatic duct drains only the right head and neck, right upper limb and right hemithorax into the right venous angle.

The testis develops on the posterior abdominal wall and descends carrying its vessels and lymphatics, so testicular lymph runs with the testicular vessels to the para-aortic nodes at L2. Scrotal skin, a different embryological territory, drains to the superficial inguinal nodes, which is why orchidectomy is done through an inguinal incision with high cord ligation rather than through the scrotum.

It is the medial node of the left supraclavicular group, sitting at the termination of the thoracic duct, so tumour emboli from any abdominal or pelvic organ can lodge there. A palpable hard node is Troisier's sign, classically from gastric adenocarcinoma but also pancreatic, oesophageal, colonic, renal, testicular and ovarian primaries, and it signifies distant (M1) disease.

They are defined by pectoralis minor: level I lateral and inferior to it, level II deep to it (including Rotter's interpectoral nodes), and level III medial to it at the apex. Standard axillary clearance takes levels I and II; adding level III raises lymphoedema risk substantially for little extra staging information.

The duct ascends to the right of the midline from T12 and only crosses to the left at about T5, so a tear below T5 spills chyle into the right pleural space and a tear above T5 into the left. This is why oesophagectomy typically produces a right chylothorax and left neck dissection a left-sided leak.

Pleural fluid triglycerides above 1.24 mmol/L (110 mg/dL) or demonstrable chylomicrons confirm it, while a level below 0.56 mmol/L (50 mg/dL) effectively excludes it. Treat with drainage and a low-fat diet using medium-chain triglycerides (absorbed directly into the portal vein) or parenteral nutrition with octreotide, reserving duct ligation or embolisation for persistent high-volume loss.

Net capillary filtration under the Starling forces leaves about 2 to 4 litres a day, along with escaped plasma protein, in the interstitium. Lymphatic capillaries take it up through overlapping endothelial flaps opened by anchoring filaments, and valved lymphangions plus the skeletal muscle and respiratory pumps drive it centrally.