Vascular Anatomy in Clinical Practice

The arterial and venous systems are not simply pipes — their anatomy determines which vessels are used for clinical access, where aneurysms form, how thrombosis propagates, and why certain interventions succeed or fail. Vascular anatomy is a bridge between structural knowledge and daily clinical decision-making in cardiology, vascular surgery, interventional radiology, and emergency medicine. This guide is for educational purposes only.

## Arterial Access Points

Clinicians routinely access the arterial system for haemodynamic monitoring, blood gas sampling, and endovascular procedures. The most common sites exploit anatomical properties — large calibre, superficial location, and the ability to apply compressive haemostasis against a firm structure. The femoral artery is the preferred access site for most endovascular procedures (coronary angiography, peripheral angioplasty, transcatheter aortic valve implantation — TAVI). It is accessed in the common femoral artery segment, between the inguinal ligament superiorly and the bifurcation into superficial and deep femoral arteries inferiorly — a segment overlying the femoral head, allowing bony compression after sheath removal. The artery is located at the midinguinal point (midpoint between the anterior superior iliac spine and the pubic symphysis), medial to the femoral nerve and lateral to the femoral vein (the mnemonic "NAVEL" from lateral to medial: Nerve, Artery, Vein, Empty space, Lymphatics). Radial artery access (at the wrist, between the flexor carpi radialis tendon and the radius) is increasingly preferred for coronary procedures because the radial pulse is easily palpable and the dual blood supply (radial and ulnar arteries anastomosing in the palmar arches) provides a safety net if the radial artery thromboses post-procedure.

## Aortic Anatomy and Aneurysms

The aorta — the body's main arterial conduit — is divided into the ascending aorta, the aortic arch (from which the brachiocephalic trunk, left common carotid, and left subclavian arteries arise), the descending thoracic aorta, and the abdominal aorta. The aorta enters the abdomen through the aortic hiatus of the diaphragm at T12, lying anterior to the vertebral column, and bifurcates into the common iliac arteries at the level of L4 (approximately at the level of the umbilicus — a landmark used in cardiopulmonary resuscitation and emergency situations).

Abdominal aortic aneurysm (AAA) — pathological dilatation of the abdominal aorta exceeding 3 cm (normal approximately 2 cm in diameter) — occurs almost exclusively below the renal arteries (infrarenal), where the aortic wall is thinnest and has the fewest vasa vasorum to supply the aortic media. The infrarenal aorta is also subject to reflective pressure waves from the aortic bifurcation, amplifying pulsatile stress. Risk factors include male sex, smoking, hypertension, and a family history. A ruptured AAA leaks blood into the retroperitoneal space, producing the classic triad of severe back/flank pain, a pulsatile abdominal mass, and haemodynamic shock — a surgical emergency. Endovascular aneurysm repair (EVAR) deploys a stent-graft via the femoral arteries, relying on adequate "neck" anatomy (sufficient length of normal aorta below the renal arteries to seal the graft).

Thoracic aortic aneurysms (TAAs) most commonly involve the ascending aorta, where dilatation stretches the aortic valve annulus and causes aortic regurgitation, and the aortic arch. Ascending TAAs are associated with bicuspid aortic valve (2% of the population, with associated medial wall abnormalities) and Marfan syndrome (FBN1 mutation causing fibrillin-1 deficiency and medial degeneration). Aortic dissection — a tear in the intima allowing blood to enter the media and create a false lumen — most commonly initiates in the ascending aorta at the sinotubular junction (where haemodynamic stress is greatest) or just distal to the left subclavian artery origin.

## Deep Vein Thrombosis: Venous Anatomy

Deep vein thrombosis (DVT) of the lower extremity most commonly begins in the calf veins — the paired venae comitantes of the tibial arteries and the large soleal sinusoids — and propagates proximally. The deep veins of the lower extremity run alongside the major arteries: the popliteal vein (behind the knee), the femoral vein (in the adductor canal and femoral triangle), and the common femoral vein (below the inguinal ligament), which continues as the external iliac vein above the inguinal ligament. The common iliac veins join at L5 to form the inferior vena cava (IVC), which runs to the right of the aorta and drains into the right atrium.

The anatomy of the left iliac venous system creates an additional risk for left-sided DVT: the left common iliac vein is compressed between the right common iliac artery (which crosses over it) and the fifth lumbar vertebra — a variant known as May-Thurner (or Cockett) syndrome — which can cause chronic venous obstruction and predispose to iliofemoral DVT.

Proximal DVT (popliteal and above) carries the risk of pulmonary embolism (PE): thrombus may propagate into the femoral and iliac veins and embolise through the right heart into the pulmonary arteries. The anatomy of the pulmonary arteries (the right and left pulmonary arteries arising from the pulmonary trunk, each dividing into lobar and segmental branches) determines where emboli lodge — most commonly at the bifurcation (saddle embolus) or in the lobar branches.

## Varicose Veins

Varicose veins are dilated, tortuous superficial veins of the lower extremity, resulting from incompetence of the valves in the great saphenous vein (GSV) or small saphenous vein (SSV) and their perforating tributaries. The great saphenous vein originates at the dorsal venous arch of the foot, passes anterior to the medial malleolus (where it is consistently palpable and used for emergency venous cutdown), ascends along the medial thigh, and drains through the saphenofemoral junction (SFJ) into the common femoral vein approximately 3.5 cm inferolateral to the pubic tubercle. The SFJ is the most important anatomical landmark in varicose vein surgery; the GSV's tributary — the superficial epigastric, superficial iliac circumflex, and external pudendal veins — must be carefully identified and ligated at this junction to prevent recurrence. The small saphenous vein runs from the lateral foot, behind the lateral malleolus, and drains into the popliteal vein at the saphenopopliteal junction (SPJ), the level of which is variable and must be confirmed by duplex ultrasound preoperatively.

## Coronary Artery Anatomy and Disease

The two coronary arteries arise from the aortic sinuses (of Valsalva) — the pockets of aorta immediately above the aortic valve leaflets. They run in the atrioventricular groove and interventricular grooves on the cardiac surface. The left coronary artery arises from the left aortic sinus, passes behind the pulmonary trunk, and divides almost immediately into the left anterior descending (LAD) artery (which descends in the anterior interventricular groove, supplying the anterior wall of the left ventricle, the anterior interventricular septum, and the apex) and the left circumflex artery (which passes in the left atrioventricular groove to supply the lateral and posterior wall of the left ventricle). The right coronary artery arises from the right aortic sinus, descends in the right atrioventricular groove, and in approximately 70% of people (right dominant circulation) gives rise to the posterior descending artery (PDA) supplying the inferior ventricular wall and inferior septum. The LAD is the most commonly occluded coronary artery — occlusion at its proximal segment (the "widow maker") causes anterior ST-elevation myocardial infarction (STEMI) with haemodynamic compromise. Percutaneous coronary intervention (PCI) with stent deployment has replaced thrombolysis as the standard treatment for STEMI at centres with 24-hour catheter laboratory access.