The left image shows a hyperdense right middle cerebral artery (MCA), which can be seen with acute thrombus. The right image shows hypodensity of the right insular cortex anteriorly, caudate nucleus, and lentiform nucleus, representing infarct related to the right MCA thrombus.
The bottom left image shows a coronal view of the right MCA thrombus (red arrow). The bottom right image shows confirmation of the right MCA occlusion (red arrow) on CTA of the head.
Discussion
The hyperdense MCA sign on non-contrast imaging can indicate acute thrombus. The same sign can be seen in the basilar artery and vertebral artery. In the setting of stroke, it is important to look for a hyperdense vessel in addition to changes in the brain related to stroke and evidence of hemorrhage. If the stroke is acute, it is possible to encounter the dense vessel sign without any changes in the brain parenchyma. This is important to identify because it allows eligible patients to benefit from intra-arterial or intra-venous thrombolytics.
It can be difficult to identify a hyperdense vessel. The first step is to ensure that it is part of your search pattern. You can compare the MCA, basilar artery, and vertebral arteries to determine if one vessel is more dense that the others. In my experience, patent vessels typically measure 30-40 houndsfield units (HU), whereas thrombosed vessels typically measure 45-68 HU. And the difference between them within the same patient is around 12-18 HU. There is overlap though, so make sure that the patient is experiencing stroke symptoms that correlate with the distribution of the affected vessel.
There is literature reporting relatively high sensitivity and specificity for hyperdense MCA in the setting of stroke with a measurement of >43 HU in the affected MCA or an MCA ratio (hyperdense MCA / contralateral MCA) > 1.2
Chrzan R, GleńA, Urbanik A. How to avoid false positive hyperdense middle cerebral artery sign detectionin ischemic stroke. Neurol Neurochir Pol. 2017Sep - Oct;51(5):395-402.
Koo CK, Teasdale E, Muir KW. What constitutes a true hyperdense middle cerebral artery sign? Cerebrovasc Dis. 2000 Nov-Dec;10(6):419-23.
Another finding that you may see is calcification within a vessel. This may represent atherosclerotic calcification or a calcified thrombus within the vessel. If the patient has stroke symptoms corresponding to that vessel, you can provide a differential and recommend CTA of the head/neck for further evaluation. Also remember that prior studies can be critical in making the right diagnosis.
Companion case
The imaging shown below is from a 70 year old man with dizziness and vertiginous symptoms who fell out of a chair with unknown head trauma.
I have provided images of the basilar artery (top left), MCA (top right), and vertebral arteries (bottom left).
Questions
Is there any difference between the vessels?
Does that vessel correspond with the patients symptoms?
