Veins & Lymphatics

The superior vena cava collects all venous blood from above the diaphragm — both upper limbs, the head and neck, and the thoracic wall — and returns it to the right atrium. Its formation at the first costal cartilage marks the sternal angle level, which is simultaneously the aortic arch, the carina, and the azygos vein's entry point. The left brachiocephalic vein is anatomically important in surgery and central line placement because it crosses anterior to all three aortic arch branches — the right brachiocephalic vein simply drops almost vertically. SVC obstruction is a clinical syndrome, not a diagnosis: the key exam feature is non-pulsatile JVP elevation with facial and arm swelling, caused most commonly by a right upper lobe bronchogenic carcinoma pressing on the thin-walled SVC.

Formed by union of left + right brachiocephalic veins behind the right 1st costal cartilage. Descends to enter right atrium at T3. Lower half is intrapericardial. Azygos vein arches over the right lung root and drains into the posterior SVC (at T4).

Fig. 4.166 — Inferior vena cava: formed at L5 by the union of the common iliac veins; receives lumbar, renal, right gonadal, right suprarenal and hepatic veins; pierces the diaphragm at T8.

Gray's Anatomy for Students, 4e

The IVC is a right-sided structure — it runs to the right of the aorta throughout the abdomen, which has surgical consequences: during right adrenalectomy the short right suprarenal vein empties directly into the IVC and tears easily; during left adrenalectomy the longer left suprarenal vein drains into the left renal vein and is less immediately dangerous. The gonadal vein asymmetry is one of the highest-yield venous anatomy facts: the left gonadal vein drains into the left renal vein at a right angle under higher hydrostatic pressure, explaining why varicoceles are almost always left-sided (90%). A left-sided varicocele that does not decompress when the patient lies down is a red flag for left renal vein obstruction — most commonly renal cell carcinoma extending tumour thrombus into the renal vein or IVC.

Formed at L5 (just below aortic bifurcation at L4) by union of right and left common iliac veins. Ascends right of aorta → passes through caval opening in diaphragm at T8 → right atrium. Right-sided structure throughout (aorta is left of midline, IVC is right).

The portal venous system is the liver's first-pass filtration highway: all blood drained from the GI tract, spleen, and pancreas must pass through the liver sinusoids before reaching the systemic circulation. This is why oral drugs are absorbed in the gut but metabolised (and sometimes inactivated) before reaching the systemic circulation — the first-pass effect. The portal vein forms behind the neck of the pancreas at L2, the SMV and splenic vein meeting there after having collected blood from the entire bowel and spleen. When portal pressure rises above 12 mmHg — most commonly from cirrhosis — blood backs up and finds collateral routes to the systemic circulation wherever the two venous systems are in anatomical contact: oesophagus (varices that bleed fatally), rectum (rectal varices, not haemorrhoids), anterior abdominal wall (caput medusae), and retroperitoneum. Budd-Chiari syndrome, by contrast, blocks the hepatic venous outflow, and its imaging hallmark — caudate lobe hypertrophy — is the anatomical consequence of that lobe's unique direct drainage into the IVC.

Portosystemic anastomoses are the anatomical sites where the portal venous system is in direct communication with systemic veins. Normally these connections carry little flow — but in portal hypertension they dilate into varices that can rupture and bleed catastrophically. The four sites are mnemonised as OARU: Oesophagus (left gastric vein meets azygos, via oesophageal veins), Anal canal (superior rectal meets middle/inferior rectal), Retroperitoneum (Veins of Retzius), and Umbilicus (paraumbilical veins radiating as caput medusae). The oesophageal site is the most dangerous: the submucosal oesophageal veins are thin-walled and unsupported, so rupture produces haematemesis that kills in minutes. Understanding which portal tributary connects to which systemic vein at each site explains exactly which vessel to look for on endoscopy, which direction to embolise, and why banding works where it does.

Fig. 3.102 — Azygos system of veins: azygos (right), hemi-azygos and accessory hemi-azygos veins draining the posterior thoracic wall and forming a portocaval / cavocaval anastomotic channel.

Gray's Anatomy for Students, 4e

The azygos system is the body's great venous bypass highway — running alongside the vertebral column in the posterior mediastinum, it drains the thoracic wall (posterior intercostal veins), the oesophagus, and the bronchi, and crucially connects the IVC below to the SVC above. This connection is what makes IVC occlusion survivable: blood from the lower limbs and pelvis can still reach the heart by flowing up the ascending lumbar veins into the azygos/hemiazygos, then into the SVC. Batson's vertebral venous plexus is the clinically crucial extension of this system — a valveless network surrounding the entire spine that explains haematogenous vertebral metastases from pelvic tumours (prostate → lumbar spine), vertebral osteomyelitis from pelvic sepsis, and even "skip" brain metastases that bypass the lungs entirely during Valsalva-type pressure rises.

Fig. 8.43 — Dural venous sinuses: superior & inferior sagittal, straight, transverse and sigmoid sinuses draining into the internal jugular vein at the jugular foramen.

Gray's Anatomy for Students, 4e

The internal jugular vein is the most direct window into right heart haemodynamics — because it communicates almost directly with the right atrium via the SVC, its filling height and waveform reflect right atrial pressure in real time. The JVP assessment uses the right IJV because the right brachiocephalic vein is short and nearly vertical; the left IJV has a longer, more angled path and is less reliable. The "danger triangle" of the face is not a surface anatomy curiosity — it is a life-threatening anatomical principle: the facial vein is valveless, so squeezing a boil between the upper lip and nose can push septic emboli retrogradely through the angular vein → superior ophthalmic vein → cavernous sinus. Cavernous sinus thrombosis presents as a septic patient with proptosis, chemosis, and painful ophthalmoplegia — CN VI palsy appears first because the abducens nerve has the least protection as it runs free through the sinus.

The two great superficial veins of the upper limb — cephalic and basilic — are not symmetrical, and the asymmetry is exactly what examiners test. Both arise from the dorsal venous rete of the hand but at opposite sides: cephalic from the radial (lateral/thumb) side, basilic from the ulnar (medial/little-finger) side. They meet in the cubital fossa via the median cubital vein, which is where clinical staff cannulate most reliably because it is large, superficial, and usually visible. In the upper arm the cephalic vein runs in the lateral bicipital groove all the way to the deltopectoral groove, then pierces the clavipectoral fascia to drain into the axillary vein — it does not drain into the brachial vein. The basilic vein, by contrast, pierces the deep fascia at mid-arm to join the brachial veins and becomes the axillary vein at the lower border of teres major. Past paper MCQ Q11 (2020) specifically tests cephalic vein anatomy.

Fig. 3.103 — Thoracic duct: begins at the cisterna chyli (L1–L2), ascends through the posterior mediastinum and drains lymph from the whole body except the right upper quadrant into the left venous angle.

Gray's Anatomy for Students, 4e

The thoracic duct is the largest lymphatic vessel in the body, draining everything except the right upper quadrant — that means roughly 75% of the body's lymph, including all intestinal chyle and lymph from both lower limbs, the pelvis, the left chest, and the left side of the head and neck. It originates from the cisterna chyli at L1/L2, enters the thorax through the aortic hiatus, climbs on the right side of the spine, then crosses left at T4/T5 and terminates at the left subclavian–internal jugular junction. This crossing is why chyle leaks from left neck dissections but rarely right ones. The right lymphatic duct drains the right upper quadrant into the right venous angle — and in 25% of people it doesn't exist as a single duct at all, just three separate trunks draining individually. Virchow's node (left supraclavicular) is the clinical sentinel: it receives the thoracic duct's drainage, so abdominal malignancies — especially gastric carcinoma — metastasise there first.

Fig. 1.30 — Major lymphatic vessels draining into the large veins at the root of the neck — the thoracic duct (left) and right lymphatic duct (right).

Gray's Anatomy for Students, 4e

Lymph nodes are the surveillance posts of the immune system — bean-shaped filters stationed along lymphatic channels that intercept antigens, bacteria, tumour cells, and pathogens before they reach the bloodstream. Their anatomical position defines which region each node drains, making them invaluable clinical indicators: a tender, enlarged node signals local infection, while a hard, fixed, non-tender node suggests metastatic malignancy. Knowing which station drains which territory lets you locate the primary tumour from the involved node alone — testicular cancer spreads to para-aortic nodes, not inguinal ones, because the testis descends from L1 carrying its lymphatics with it. The clinical examination of lymph nodes (size, consistency, tenderness, mobility, overlying skin) distinguishes reactive from malignant lymphadenopathy before biopsy is needed.

The spleen is simultaneously an immune organ and a blood filter — it destroys aged red cells, phagocytoses opsonised bacteria, and produces IgM antibodies, making it the first line of defence against encapsulated organisms. Anatomically it hides under the 9th–11th ribs in the left hypochondrium, which is why you only feel it when it is at least twice its normal size. Its unique clinical signature is the splenic notch — a notch on the superior border that you can palpate as it pushes below the costal margin; no other abdominal mass has this feature. The splenorenal ligament tethers the splenic vessels and tail of the pancreas directly to the hilum, which is why distal pancreatitis or surgery can injure the splenic vasculature simultaneously. After splenectomy, the patient loses polysaccharide capsule immunity permanently, making vaccination and prophylactic antibiotics non-negotiable for life.

The leg has two venous systems — a deep system buried within the muscle compartments that carries 90% of returning blood, and a superficial system sitting in the subcutaneous fat that is visible, strippable, and clinically notorious for dilating into varicose veins. The two systems communicate through perforating veins whose valves normally allow flow only from superficial to deep; when those valves fail, high-pressure deep venous blood refluxes back into the superficial system, distending and torturing it into the ropes of varicose veins. The great saphenous vein is the longest vein in the body and the surgeon's friend — used as a bypass conduit in CABG and peripheral arterial reconstruction — so understanding its course (anterior to medial malleolus, up the medial thigh, into the femoral vein at the SFJ) matters beyond venous surgery. Varicose veins are often dismissed cosmetically, but the CEAP classification recognises a spectrum from thread veins to venous ulcers, all driven by the same underlying venous hypertension.

DVT and pulmonary embolism are the same disease at different stages of its natural history — a clot that forms in the deep venous system of the leg can detach, travel through the right heart, and lodge in the pulmonary arterial tree, converting a local problem into a life-threatening emergency. Virchow's triad (stasis, hypercoagulability, endothelial damage) remains the conceptual framework for every risk factor you will memorise, from long-haul flights to Factor V Leiden. The Wells score turns clinical suspicion into a probability, and D-dimer — highly sensitive but notoriously non-specific — is powerful only as a rule-out tool in low-probability patients. The great challenge of PE is that its classic ECG finding (S1Q3T3) appears in only 20% of cases, so a high index of clinical suspicion followed by CTPA is the diagnostic cornerstone. Treatment has shifted dramatically toward DOACs, which have replaced warfarin in most situations without the need for INR monitoring.

Lymphoedema is not just "swelling" — it is a chronic, progressive disease caused by the failure of lymphatic drainage to remove the daily protein load from the interstitium. Unlike venous oedema, which is a low-protein transudate that pits easily and resolves overnight with leg elevation, lymphoedema is protein-rich, triggering a relentless inflammatory response that over months to years converts the soft, pitting swelling into leathery, non-pitting fibrosis. The clinical hallmark is Stemmer's sign: inability to pinch the dorsal skin of the base of the second toe because it is thickened and fibrotic. Globally, filariasis (Wuchereria bancrofti) is the leading cause; in clinical practice in Sri Lanka and the UK, post-cancer treatment lymphoedema — especially after breast cancer axillary clearance — dominates. The most feared long-term complication is Stewart-Treves syndrome: lymphangiosarcoma arising in chronically lymphoedematous tissue, carrying a 5-year survival of only ~10%.