Abdominal Aortic Aneurysm Examination OSCE — Palpation, Screening, and Rupture Signs

Introduction

Abdominal aortic aneurysm (AAA) is a life-threatening condition that is often asymptomatic until rupture. The OSCE tests your ability to palpate for the aorta correctly, recognise the features of an aneurysm, identify rupture signs, and explain the NHS screening programme.

Anatomy

The abdominal aorta runs from the diaphragm (T12) to the aortic bifurcation at L4 (level of the umbilicus). It lies slightly left of the midline. The normal aortic diameter is under 3 cm.

Palpating the Abdominal Aorta

Technique

1. 1Patient supine, abdomen relaxed (ensure bladder is empty)
2. 2Warm hands; ask about pain before palpating
3. 3Place both hands flat on the abdomen either side of the midline, just above the umbilicus
4. 4Press firmly downward toward the spine
5. 5Feel for the aortic pulsation
6. 6Assess whether the aorta is: pulsatile only (transmitted pulsation — e.g. from overlying mass) OR expansile (hands pushed outward and upward with each beat — true aneurysm)

Estimating Size

Attempt to estimate the diameter between your thumbs. A width greater than a two-finger breadth (approximately 3-4 cm) warrants further investigation.

Associated Examination

Bruit

Auscultate over the aorta and renal arteries (flanks). A systolic bruit may indicate turbulent flow within the aneurysm or renal artery stenosis.

Peripheral Vascular Assessment

• Femoral, popliteal, posterior tibial, and dorsalis pedis pulses
• Absent or reduced peripheral pulses suggest concurrent peripheral arterial disease (common in AAA patients)
• Bilateral absence of femoral pulses = aortoiliac occlusion (Leriche syndrome)

Iliac Arteries

Palpate the iliac fossae for iliac aneurysms (common extension of AAA).

Signs of Ruptured AAA — Surgical Emergency

NHS AAA Screening Programme

All men aged 65 in England are invited for a one-off abdominal ultrasound scan. The rationale:

• AAA is 6 times more common in men
• Risk factors: age over 65, male sex, smoking, hypertension, family history, connective tissue disorders (Marfan's, Ehlers-Danlos)
• Screening reduces AAA-related mortality by 50% in men

Women are not routinely screened (lower incidence).

Risk Factors

How to Present

"On examination of the abdomen, there was a pulsatile, expansile mass in the epigastrium and central abdomen, estimated at approximately 5 cm in diameter. A systolic bruit was audible over the mass. Peripheral pulses were present bilaterally with reduced amplitude in the left posterior tibial pulse. There was no evidence of haemodynamic compromise. These findings are consistent with an abdominal aortic aneurysm. Given the estimated size of 5 cm, I would refer urgently to vascular surgery for CT angiography and surgical planning."

"How do you differentiate an expansile from a merely pulsatile abdominal mass?"

A pulsatile mass transmits the aortic pulsation from an adjacent structure — the hands move up and down but do not move apart. An expansile mass is a true aneurysm: the aortic wall itself expands with each systole, pushing the examining hands both upward and outward so the distance between them increases. Expansility confirms an aneurysm; transmitted pulsation is a normal finding with any mass overlying or adjacent to the aorta.

"What are the signs and symptoms of a ruptured AAA?"

The classic triad is: sudden severe tearing or ripping central abdominal or back pain, a pulsatile expansile abdominal mass, and haemodynamic shock (hypotension, tachycardia, pallor, syncope). The pain may radiate to the loin, groin, or legs. Not all three features are always present — a retroperitoneal haematoma can temporarily tamponade the bleed, creating a brief period of relative haemodynamic stability before catastrophic collapse.

"At what diameter is an AAA referred for surgical repair?"

An AAA of 5.5 cm or greater in maximum diameter is referred for elective surgical consideration, as the annual rupture risk (approximately 25%) exceeds the surgical mortality risk. Any symptomatic AAA (pain, tenderness) or rapidly expanding aneurysm (greater than 1 cm per year) is referred urgently regardless of size. Smaller aneurysms are followed with ultrasound surveillance at intervals determined by size.

"Who is invited for AAA screening and why?"

All men aged 65 in England are invited for a one-off abdominal ultrasound scan through the NHS AAA screening programme. Men are targeted because AAA is six times more common in men than women. The programme has been shown to reduce AAA-related mortality by approximately 50% in the screened population by detecting aneurysms before rupture. Women are not routinely screened due to lower prevalence and different risk profile.

Related guides: Peripheral Vascular Examination OSCE | Abdominal Examination OSCE | A&E Assessment OSCE