A 72-year-old woman with a 10-year history of diabetes and hypertension presents with sudden onset of pain and coldness in the left foot. Clinical examination reveals absent femoral and popliteal pulses, pale skin, and intact sensation. The patient is haemodynamically stable. Which investigation is most appropriate to differentiate between arterial thrombosis and embolism before intervention?

Explanation

## Differentiating Arterial Thrombosis from Embolism in Acute Limb Ischemia **Key Point:** Contrast-enhanced CT angiography (CTA) of the heart, aorta, and lower limb arteries is the single best investigation to both confirm acute limb ischemia AND differentiate thrombotic from embolic occlusion, guiding the choice of intervention. ### Clinical Distinction: Thrombosis vs Embolism | Feature | Thrombosis | Embolism | |---|---|---| | **Onset** | Gradual (hours–days) | Sudden (minutes–hours) | | **Risk factors** | Atherosclerosis, diabetes, smoking | AF, recent MI, valvular disease | | **Occlusion site** | At atherosclerotic plaque (aorta, iliac, femoral) | Bifurcations (aortic, femoral) | | **Collaterals** | Well-developed | Absent or poor | | **Imaging clue** | Atherosclerotic disease proximal & distal | Normal proximal vessels, sudden cutoff | ### Why CTA with Cardiac Imaging? 1. **Identifies source of embolism**: Visualizes the heart (AF, thrombus, valvular disease), aorta (atheroma, dissection), and proximal arteries. 2. **Assesses atherosclerotic burden**: Shows calcification and stenotic disease in the aorta and iliac vessels—markers of thrombosis. 3. **Evaluates collateral circulation**: Thrombosis typically has well-developed collaterals; embolism does not. 4. **Guides intervention**: Emboli → thrombolysis or thrombectomy; thrombosis → may require longer thrombolysis or surgery. ### Clinical Context This patient has **acute limb ischemia (Rutherford IIa: pain, pallor, absent pulses, intact sensation)**. The sudden onset and absent femoral pulse suggest **embolic occlusion**, but CTA will confirm by imaging: - The heart (source of embolus) - The aorta and iliac vessels (atherosclerotic burden) - The occlusion site and runoff **High-Yield:** CTA is the only single investigation that provides both diagnostic confirmation and pathophysiological differentiation, enabling optimal triage to thrombolysis vs thrombectomy vs surgery. ### Why Not the Other Options? | Investigation | Limitation | |---|---| | **Transoesophageal echocardiography (TOE)** | Invasive; does not visualize peripheral arteries or aortic atheroma; requires sedation; not practical in acute setting | | **Carotid duplex** | Assesses carotid arteries, not relevant to lower limb ischemia or cardiac source | | **D-dimer** | Elevated in both thrombosis and embolism; non-specific; does not differentiate or guide intervention | **Clinical Pearl:** In acute limb ischemia, the **combination** of clinical presentation (sudden vs gradual), risk factor profile (AF vs atherosclerosis), and imaging findings (collaterals, atheroma, cardiac source) determines whether the occlusion is thrombotic or embolic.