The dense or hyperdense MCA sign refers to the appearance of the middle cerebral artery (MCA) on CT. It has been associated with poor outcome.
There is increased attenuation of the proximal portion of the MCA and it is often associated with thrombosis of the M1 MCA segment. It is one of the early signs of ischaemic stroke: MCA infarct.
The same pathological process can give an MCA dot sign when seen end on.
The sign is typically seen within 90 minutes of the ischemic event, and thus, it is very important for radiologists to recognize this sign. It can save the patient in 'golden hour' of thrombolysis (3 hours for intravenous tPA, and 6 hours for intra-arterial thrombolysis). This sign has approx. 100% sensitivity, however only 30% specificity.
It is usually associated with another important sign of acute ischaemia-insular ribbon sign.
Identification of the dense artery sign is often based on subjective interpretation and false positives may occur. One study aiming to define criteria for the sign determined that measuring Hounsfield units on the CT scan could differentiate between the dense MCA sign associated with ischemic stroke and that caused by false positives. Specifically, the combination of greater than 43 Hounsfield units and an MCA ratio of greater than 1.2 was diagnostic of a dense MCA sign associated with acute ischemic stroke.
There are occasional reports of a hyperdense MCA sign seen with HSV encephalitis
False-positives: (asymptomatic patients-usually bilateral):
Different tissues in the body give different shades on CT scan according to their densities. These shades are described by CT number or Hounsfield unit. For example bone appear white on ct scan with HU of 1000 and air appear black having HU of -1000. There are many shades in between these two which are important in recognizing normal tissues and also pathologies.
Following CT image showing tissues with different densities. I found calcified aorta an interesting thing to pick :-p
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