These narrowed channels are likely sites of blockage from clots. In the case of the carotids, these constrictions can be cleaned out surgically. This operation, called carotid endarterectomy, is a relatively low-risk procedure that, unfortunately, has no equivalent in the vertebral arteries, which are surrounded by bone. Some preliminary work has been done, however, in reopening vertebral arteries with balloon angioplasty, in which a catheter is worked into position within the blockage and a tiny balloon at its tip is inflated to flatten the obstruction against the artery wall. The presence of stroke-producing conditions can be determined by a variety of methods, from listening with a stethoscope for a characteristic whistling sound in the carotid arteries, to ultrasound imaging or cerebral angiograms to detect blockages and blood flow disturbances within the arteries, to magnetic resonance scans, which can show aneurysms and sites of previous bleeding in the brain.
Strokes tend to run in families, and smokers are at additional risk as well.