## Hyperdense Artery Sign in Acute Stroke **Key Point:** The hyperdense artery sign (HAS) represents a thrombus or embolus within the arterial lumen, appearing as increased attenuation (density) on non-contrast CT. ### Imaging Characteristics | Feature | Details | |---------|----------| | **Appearance** | Increased density (>60 HU) within arterial lumen | | **Common locations** | Middle cerebral artery (MCA), basilar artery, internal carotid artery (ICA) | | **Timing** | Visible within first 6–24 hours of symptom onset | | **Sensitivity** | 25–60% for acute thrombosis | | **Specificity** | High (>95%) when present | ### Mechanism The increased density is due to: 1. Fresh thrombus contains deoxyhemoglobin and fibrin (higher atomic number than blood) 2. Stasis of blood increases local hematocrit 3. Contrast pooling in slow flow (if performed with contrast) **High-Yield:** The hyperdense artery sign is an early indicator of acute arterial occlusion and may be the only CT finding before infarction becomes visible (typically 6–12 hours). ### Clinical Significance - Suggests acute thromboembolism requiring urgent thrombolysis or thrombectomy - More commonly seen in proximal large-vessel occlusions (MCA, basilar) - May fade as thrombus organizes or recanalization occurs - Not present in all acute strokes (lower sensitivity in small arteries) **Clinical Pearl:** A hyperdense artery on CT in the first few hours of stroke is a red flag for time-critical intervention eligibility. 
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