## The Hyperdense Middle Cerebral Artery Sign **Key Point:** The hyperdense MCA sign is a CT finding of acute arterial thrombus within the middle cerebral artery, appearing as a focal area of increased attenuation within the MCA lumen on non-contrast CT. ### Imaging Characteristics - **Appearance:** Hyperdense dot or linear opacity within the MCA trunk or proximal branches - **Density:** Typically 60–90 HU (compared to normal brain ~30–40 HU) - **Cause:** Acute thrombus with high hematocrit and protein concentration - **Timing:** Most visible in the first 6–8 hours; may fade as thrombus becomes more organized ### Clinical Significance - **Marker of acute ischemic stroke:** Indicates large vessel occlusion (LVO) - **Prognostic value:** Associated with worse outcomes if not rapidly reperfused - **Sensitivity:** Present in only 30–50% of acute MCA occlusions (not a sensitive sign) - **Specificity:** Highly specific when present; rarely seen in normal vessels ### Differential Considerations - ~~Hyperdensity in subarachnoid space~~ = subarachnoid hemorrhage (SAH), not arterial thrombus - ~~Iron deposition in basal ganglia~~ = chronic pathology (Parkinson disease, hemochromatosis), not acute stroke - ~~Vasospasm~~ = narrowing of vessel lumen without hyperdensity on non-contrast CT **High-Yield:** The hyperdense MCA sign is a direct indicator of acute thrombotic occlusion and warrants urgent intervention (thrombolysis or thrombectomy). **Clinical Pearl:** The sign may be subtle and easily missed; comparison with the contralateral MCA is helpful. Its absence does NOT exclude acute MCA occlusion. [cite:Harrison 21e Ch 435] 
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