The hyperdense MCA sign refers to focal hyperattenuation of the middle cerebral artery (MCA) on non-contrast brain CT and is due to intraluminal thromboembolic material. It is the earliest visible sign of MCA infarction and is seen within 90 minutes after the event 1. It is also known as Gács sign. The MCA dot sign and hyperdense basilar tip sign are due to clot at these respective locations.
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Pathology
This sign is due to embolic red blood clot arising from the heart or arteries. The high attenuation is predominantly caused by the high globin concentration in the clot. The clot usually lodges in the proximal MCA.
By contrast, smaller white clot emboli typically lodge in the M1 or M2 segments and are not visible on non-contrast CT 9. These globin-poor clots have similar attenuation to blood.
Sensitivity and specificity
The sensitivity of this CT sign for embolism is only about 30% but its specificity is about 90% 6.
Radiographic features
CT
The hyperattenuating clot typically occludes the proximal MCA, often protruding into the terminal supraclinoid internal carotid artery. Thin sections are important to avoid partial volume averaging. If CT angiography (CTA) is performed, enhancement is typical and is due to the permeable nature of red clot. Delayed phase CTA may demonstrate the distal end of the clot allowing an estimate of length.
MR
Susceptibility-weighted imaging (SWI) is exquisitely sensitive to the MCA clot and distal embolic shower due to blooming artefact.
Treatment and prognosis
Red clot fragments easily and typically responds to recanalization therapy, both t-PA and mechanical thrombectomy. Proximal balloon occlusion helps to avoid distal embolization. Success is adversely affected by length 11.
Differential diagnosis
Hyperattenuating MCA in the context of corresponding acute stroke is diagnostic.
Atherosclerosis can cause hyperattenuating MCA due to calcification.
Polycythemia or hemoconcentration cause generalized intravascular hyperattenuation due to high globin concentration.
Relative MCA hyperattenuation compared with temporal lobe occurs in mature cerebral infarction and HSV encephalitis 4.
History and etymology
The dense artery sign was first described by Gyula Gács (fl. 2022), in 1983, a renowned, still active Hungarian neurologist-psychiatrist, who works in Budapest 7; hence it is not uncommon to hear it referred to as the "Gács sign" by Hungarian physicians.
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