Lymphatic system
Lymphatic system and lymph node groups by region
Lymph runs from blind-ended capillaries through valved vessels and chains of nodes to the thoracic duct and right lymphatic duct, and tumours spread along the same predictable routes. CPSP asks where each organ drains first, which nodes are seen on CT, ultrasound and PET, how the thoracic duct runs, and what normal and abnormal nodes look like.
How lymph moves
- Lymphatic capillaries are blind-ended with loose overlapping endothelial junctions, so they take up protein, cells and particles too large for blood capillaries. This is why technetium-99m colloid injected between the toes outlines the leg lymphatics on lymphoscintigraphy.
- Collecting lymphatics have valves and smooth muscle that contracts rhythmically, pushing lymph in pulses even in a still limb; muscle and arterial pulsation help.
- Chyle is milky because intestinal lacteals carry chylomicrons (triglyceride); chylous ascites appears only once the patient eats normally.
Lymph nodes on imaging
- Lymph enters through afferent vessels on the convex surface and leaves at the hilum. B cells lie in cortical follicles, T cells in the paracortex. The spleen has no afferent lymphatics.
| Feature | Benign or reactive node | Malignant node |
|---|---|---|
| Shape | Oval (long axis much greater than short) | Round |
| Hilum | Bright fatty hilum | Hilum lost |
| Vessels | Hilar | Peripheral or chaotic |
| Other | Smooth | Necrosis, irregular margin, extracapsular spread |
- PET-CT: FDG uptake reflects glucose use, so activated inflammatory cells in tuberculosis or sarcoidosis are also avid; uptake does not prove cancer.
- Enlarged nodes draining a recent vaccination site are reactive.
- Hodgkin lymphoma spreads to contiguous node groups; non-Hodgkin lymphoma is often non-contiguous.
Thoracic duct and right lymphatic duct
- Cisterna chyli: at L1–L2, right of the aorta behind the right crus; injured at para-aortic dissection (chylous ascites).
- Thoracic duct passes through the aortic hiatus, ascends right of the midline between aorta and azygos vein, crosses to the left at about T5, then runs left of the oesophagus to end at the left venous angle (internal jugular and subclavian veins). Injury below T5 gives a right chylothorax, above T5 a left one.
- It drains everything except the right side of the head and neck, right arm and right chest, which go to the right lymphatic duct at the right venous angle. A leak there after right supraclavicular surgery is clear, not milky.
- Virchow node (left supraclavicular) receives abdominal tumour cells through the thoracic duct.
Head and neck
| Level | Nodes | Typical sources |
|---|---|---|
| I | Submental and submandibular | Lower lip (lateral part to submandibular), anterior tongue, floor of mouth, external nose |
| II | Upper jugular (jugulodigastric) | Tonsil, tongue, pharynx |
| III | Middle jugular (jugulo-omohyoid, where omohyoid crosses the internal jugular vein) | Tongue |
| IV | Lower jugular | Larynx, thyroid, oesophagus |
| V | Posterior triangle | Nasopharynx, scalp |
| VI | Central compartment | Papillary thyroid cancer |
- Posterior third of the tongue and midline lesions drain to both sides. The vocal folds have very few lymphatics, so glottic cancer rarely spreads to nodes.
- Rubella classically enlarges suboccipital and postauricular nodes.
Thorax
- Lung lymph runs intrapulmonary, hilar, then mediastinal nodes.
- Subcarinal nodes below the tracheal bifurcation splay the main bronchi, widen the carina and indent the oesophagus. Aortopulmonary window nodes receive the left upper lobe.
- Sarcoidosis: symmetrical lobulated bilateral hilar nodes separated from the heart borders, with right paratracheal nodes.
- Lymphangitis carcinomatosa (stomach, breast, lung primaries): irregular beaded thickening of the interlobular septa on high-resolution CT.
- Tumour in the bare area of the liver reaches diaphragmatic and paracardiac nodes through lymphatics crossing the diaphragm.
Abdomen and pelvis
- Gut nodes follow the arteries: epicolic, paracolic, intermediate (along the named branches), then main nodes at the artery's origin. Sigmoid cancer goes along the sigmoid arteries to the IMA origin; caecal cancer to ileocolic nodes; rectal cancer first to mesorectal nodes.
| Organ | First nodes on staging CT |
|---|---|
| Right testis | Interaortocaval nodes near L1–L2 |
| Left testis | Left para-aortic, just below the left renal vein |
| Kidney | Para-aortic at the renal hilum on the same side |
| Ovary, uterine fundus | Para-aortic (with the ovarian vessels) |
| Cervix, upper vagina | Obturator, internal and external iliac |
| Bladder lateral wall | External iliac |
- A testis removed through the scrotum adds inguinal nodes to its drainage.
Groin and lower limb
- Superficial inguinal nodes: the horizontal group below the inguinal ligament drains the abdominal wall below the umbilicus, buttock, perineum, anal canal below the pectinate line, lower vagina, vulva, scrotum and, along the round ligament, the uterine cornu. The vertical group along the great saphenous vein drains the leg, including the medial toe.
- The lateral heel and foot drain with the small saphenous vein to popliteal nodes.
- Deep inguinal nodes lie medial to the femoral vein (one in the femoral canal, which normally holds fat, lymph vessels and a node); they receive the glans. Femoral triangle, lateral to medial: nerve, artery, vein, lymphatics.
- Midline skin (vulva, back near the spine, anterior abdomen) can drain to both sides; skin above the umbilicus drains to the axilla.
- Filariasis: dilated scrotal lymphatics with moving echoes (live adult worms, "filarial dance") on ultrasound.
Remember Nodes follow arteries: find the artery that supplies an organ and you have found its nodes.
Exam trap The thoracic duct crosses at T5: injury below gives a right chylothorax, above gives a left one.
Exam trap A round node that has lost its fatty hilum is suspicious whatever its size.
Test yourself on this topic
5 of the 52 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A 52-year-old woman with known gastric adenocarcinoma has worsening breathlessness. High-resolution CT shows irregular, beaded thickening of the interlobular septa and of the bronchovascular bundles in both lungs, with normal lung architecture between them and no fever. What is the most likely cause?
Answer: Tumour within pulmonary lymphatics
Lymphangitis carcinomatosa is the spread of tumour cells within the lymphatics of the lung, often from cancers of the stomach, breast, lung, pancreas or prostate. Tumour and desmoplasia in the septal and peribronchovascular lymphatics give nodular, beaded thickening of the septa and bronchovascular bundles, while the lobular architecture is preserved. Oedema gives smooth septal thickening, and fibrosis distorts the architecture with honeycombing.
Lymphangitis carcinomatosa
- Tumour in lung lymphatics
- Beaded septal thickening
- Thick bronchovascular bundles
- From stomach, breast, lung, pancreas
Remember Beaded septa in a cancer patient: lymphangitic spread.
Exam trap Beaded rather than smooth septal thickening is the key feature separating tumour from oedema.
Why the other options are wrong
- Haematogenous nodular metastases These form discrete round nodules, not beaded septa.
- Pulmonary oedema from heart failure Septal thickening in oedema is smooth, with effusions and a large heart.
- Idiopathic pulmonary fibrosis Causes subpleural honeycombing and distortion, not beaded septa.
- Pneumocystis pneumonia Causes ground-glass change in an immunosuppressed patient.
In a man with sigmoid colon carcinoma, nodes along the sigmoid arteries contain tumour. Where will the next (main) group of nodes lie?
Answer: Inferior mesenteric artery origin
Colonic lymph follows the arteries: epicolic, paracolic, intermediate nodes along the named branches, and then main nodes at the origin of the parent artery. The sigmoid and descending colon are supplied by the inferior mesenteric artery, so their lymph drains to nodes along its branches and then to the inferior mesenteric nodes at its origin from the aorta. This is why the inferior mesenteric artery is ligated high in a cancer resection.
Colonic lymph nodes
- Lymph follows the arteries
- Sigmoid: sigmoid arteries
- Then inferior mesenteric nodes
- Basis of high ligation
Remember Hindgut lymph follows the inferior mesenteric artery.
Exam trap Lymph from the colon goes with the arteries, not with the inferior mesenteric vein.
Why the other options are wrong
- Along the superior mesenteric artery Drains the midgut, up to the distal transverse colon.
- Along the internal iliac artery Drains the lower rectum and pelvic organs.
- Around the coeliac trunk Drains the foregut.
- Along the middle colic artery A branch of the superior mesenteric artery supplying the transverse colon.
A 45-year-old woman notices a slightly tender lump in her left axilla 10 days after a vaccine injection into her left deltoid. Two small, mobile left axillary nodes are felt; the right axilla and both breasts are normal on examination. What is the most likely explanation?
Answer: Reactive nodes after the recent vaccination
Lymph from the skin and muscle of the deltoid region drains through the upper limb lymphatics to the lateral and apical axillary nodes on the same side. A vaccine stimulates an immune response in these draining nodes, with follicular (B-cell) hyperplasia and paracortical expansion, so they enlarge and may be tender. Small, mobile, unilateral nodes on the vaccinated side within weeks of the injection, with normal breasts, are reactive and settle over a few weeks. Persistent or hard, fixed nodes need further assessment.
Post-vaccination nodes
- Deltoid drains to same-side axilla
- Follicular hyperplasia, paracortical expansion
- Within weeks of the injection
- Usually settle on follow-up
Remember Ask about recent vaccines before calling axillary nodes suspicious.
Exam trap Give vaccines in the arm opposite a known breast cancer so that reactive nodes do not confuse staging.
Why the other options are wrong
- Metastasis from an occult breast cancer Possible, but normal breasts and a recent same-side vaccine make reaction far more likely.
- Non-Hodgkin lymphoma Lymphoma usually gives painless, rubbery nodes in several regions.
- Tuberculous lymphadenitis TB nodes are usually matted, may caseate and discharge.
- Silicone from a ruptured implant She has no implant, so silicone cannot reach her nodes.
A 24-year-old man with nodular sclerosis Hodgkin lymphoma has disease in the left neck, left supraclavicular fossa and anterior mediastinum, with nothing below the diaphragm. Which feature of Hodgkin lymphoma does this pattern illustrate?
Answer: Spread to contiguous node groups
Hodgkin lymphoma usually starts in one node group, most often in the neck or mediastinum, and spreads in an orderly way to the next connected group along the lymphatic chains. This contiguous spread makes staging predictable and lets radiotherapy fields be planned. Non-Hodgkin lymphomas more often involve scattered, non-contiguous nodes, extranodal sites and the marrow at diagnosis.
Hodgkin spread
- Starts in one node group
- Spreads to adjacent groups
- Predictable staging
- NHL: non-contiguous, extranodal
Remember Hodgkin walks from node to node; NHL jumps.
Exam trap Mesenteric nodes are rarely involved in Hodgkin lymphoma but common in non-Hodgkin lymphoma.
Why the other options are wrong
- Early haematogenous spread to marrow Marrow involvement is uncommon and late in Hodgkin lymphoma.
- Frequent extranodal disease Extranodal disease is more typical of non-Hodgkin lymphoma.
- Random, non-adjacent node involvement This describes non-Hodgkin lymphoma.
- Primary origin in the thymus Mediastinal disease is nodal; it does not arise from the thymus itself.
A 28-year-old man has a seminoma of the right testis. Where are the first lymph nodes most likely to be involved?
Answer: Interaortocaval nodes near L1–L2
The testis develops in the posterior abdominal wall and descends, taking its vessels and lymphatics with it. Its lymph follows the testicular vessels back to the lumbar nodes near the renal hila. The right testis drains mainly to interaortocaval and paracaval nodes, near where the right testicular vein enters the inferior vena cava. The left testis drains to left para-aortic nodes just below the left renal vein, into which the left testicular vein drains.
Testicular lymph
- Follows testicular vessels
- Right: interaortocaval nodes
- Left: left para-aortic, below renal vein
- Scrotum: inguinal nodes
Remember Testis lymph goes home to the renal hilum level.
Exam trap Inguinal nodes are involved only if the scrotum has been breached or the tumour invades scrotal skin.
Why the other options are wrong
- Right external iliac nodes Not the first station unless the normal route has been disturbed.
- Right superficial inguinal nodes These drain the scrotal skin, not the testis.
- Left para-aortic nodes below the left renal vein This is the landing site for the left testis.
- Nodes around the coeliac trunk These drain the foregut organs.
Where this sits in the CPSP syllabus
- Diagnostic Radiology, Paper 2: Limbs, breast and lymphatics, Lymphatic system and lymph node groups by region