Imaging description

Intravascular clot can be seen on unenhanced CT as a focal hyperattenuation and may be the only sign of acute ischemia (Fig. 1.1). A thrombosed vessel has a higher CT attenuation value than a normal vessel, because clot contains more protein and less serum than blood due to the deposition of fibrinogen and other clotting proteins and extraction of serum during the process of thrombus formation. When CT shows a focal hyperattenuation in the middle cerebral artery (MCA) this is known as the dense MCA sign. This provides not only a diagnosis of MCA territory infarct but also some prognostic information, because stroke patients who demonstrate a dense MCA sign on their initial CT do relatively poorly compared to those who do not have this sign (Fig 1.2) [1]. Clot in the basilar artery is not as common as MCA thrombus, but the same principles that lead to the dense MCA sign apply to basilar artery thrombosis (Fig. 1.1) [2]. Similarly, thrombosis of the other intracranial vessels, including the veins and dural sinuses, can be diagnosed on the basis of dense clot present within the vessel (Figs. 1.3, 1.4).