Which type of stroke is primarily caused by a blood clot?

The type of stroke primarily caused by a blood clot is ischemic stroke. This category accounts for approximately 87% of all strokes and occurs when a blood vessel supplying blood to the brain is obstructed, often by a clot that has formed in an artery due to thrombosis or that has traveled from another part of the body (embolism). The result is a decrease in blood flow and oxygen to the affected area of the brain, leading to the symptoms associated with a stroke.

In contrast, hemorrhagic strokes are caused by bleeding in or around the brain, which is not related to blood clots but rather to the bursting of a blood vessel. Transient ischemic attacks (TIAs) are temporary blockages that don't cause permanent damage and resolve quickly, while cryptogenic strokes are those for which no clear cause can be identified, often leaving medical professionals uncertain about the underlying pathology.

Thus, the primary mechanism behind ischemic strokes is the presence of a blood clot, making it the appropriate answer.