Stroke. Magnetic resonance angiography (MRA) scan of the arteries of the neck and head of a 32 year old woman after a massive cerebrovascular accident (CVA), or stroke. At bottom is the aortic arch, where the body's main artery leaves the heart. The brain is at top. The two common carotid arteries branch from the aorta and travel up the neck, before each branching again into the internal and external carotid arteries. This patient has a blocked right internal carotid artery (left) causing areas of ischaemia (lack of blood flow) in the brain's right hemisphere. The blockage may be due to a thrombus (blood clot) or embolism (air bubble or loose blood clot). Strokes can be instantly fatal, or may pass unnoticed. Symptoms can include muscle weakness, behavioural changes or paralysis.