A 58-year-old man presents to the emergency department with acute onset of severe pain, coldness, and pallor of the right lower limb for 4 hours. On examination, the limb is mottled, sensory loss is present in the foot, and dorsalis pedis pulse is absent. The patient has a history of atrial fibrillation not on anticoagulation. Which is the investigation of choice to confirm the diagnosis and guide immediate management?

Explanation

## Investigation of Choice in Acute Limb Ischemia **Key Point:** CT angiography (CTA) is the gold standard investigation for acute limb ischemia in most centres because it provides rapid, high-resolution imaging of the arterial tree, identifies the site and nature of occlusion (thrombotic vs embolic), and guides immediate revascularization decisions. ### Why CT Angiography? 1. **Speed**: Can be performed in <5 minutes, critical in time-sensitive acute ischemia. 2. **Sensitivity & Specificity**: >95% for detecting arterial occlusions and stenoses. 3. **Anatomical Detail**: Delineates the proximal and distal extent of occlusion, collateral circulation, and runoff vessels—essential for surgical or endovascular planning. 4. **Guides Triage**: Helps determine candidacy for thrombolysis vs mechanical thrombectomy vs surgery. ### Clinical Context This patient has **acute limb ischemia** (Rutherford IIb–III: sensory loss, mottling, absent pulses) likely due to **arterial embolism** (AF, sudden onset). The 4-hour window is within the "golden period" for intervention. **High-Yield:** In acute limb ischemia with clinical signs of tissue damage (sensory loss, mottling), imaging must be obtained urgently to guide revascularization. Do not delay for non-urgent tests. ### Why Not the Other Options? | Investigation | Limitation in Acute Ischemia | |---|---| | **Doppler ultrasound** | Operator-dependent; may miss proximal aortic or iliac pathology; time-consuming; poor for runoff assessment | | **MR angiography** | Contraindicated if metallic implants; slower acquisition; not suitable for unstable patients; gadolinium risk in renal failure | | **ABPI measurement** | Functional test, not anatomical; does not identify occlusion site; not diagnostic in acute setting | **Clinical Pearl:** In acute limb ischemia, clinical examination alone (Rutherford classification) guides urgency, but imaging is mandatory before any intervention to avoid unnecessary delays.