Types of Stroke
There are two main kinds of stroke, ischemic stroke, which makes up about 87% of all strokes, and hemorrhagic stroke (Roger 2012). Transient ischemic attacks (TIAs) and silent strokes are less severe types of stroke, but both can have long-term consequences such as memory impairment (Blum 2012; Wang 2013; NICE 2008; NSA 2009; Das 2008).
Ischemic stroke. An ischemic stroke arises from blockage of blood supply to part of the brain. There are 2 kinds of ischemic stroke: thrombotic and embolic.
- Thrombotic stroke. A thrombotic stroke is caused by a blood clot forming in a blood vessel leading to or in the brain and disrupting blood flow to part of the brain (NSA 2012b).
- Embolic stroke. Embolic stroke occurs when a blood vessel supplying the brain is blocked by circulating debris (ie, an embolus) that originated elsewhere in the body, such as when clots form on artificial heart valves or in the upper chamber of the heart. Embolic strokes are typically caused by blood clots (NSA 2012b).
Hemorrhagic stroke. Strokes caused by blood vessel(s) breaking and leaking blood into the brain are called hemorrhagic strokes. Hemorrhagic strokes account for about 13% of all strokes, but are responsible for more than 30% of all stroke deaths. There are 2 types of hemorrhagic stroke: subarachnoid and intracerebral (NSA 2012b, Roger 2012).
- Intracerebral hemorrhage. Intracerebral hemorrhage is the most common form of hemorrhagic stroke. It occurs when a blood vessel within the brain ruptures and leaks blood into the surrounding tissue. High blood pressure is the primary cause of this type of hemorrhage. Most intracerebral hemorrhages are accompanied by a sudden onset of symptoms, such as loss of consciousness, nausea or vomiting, numbness of the face, or severe headache with no known cause (NSA 2009a).
- Subarachnoid hemorrhage. Subarachnoid hemorrhage is usually caused by an aneurysm, a bulge in a blood vessel wall, bursting in a large artery on or near the delicate membrane surrounding the brain. Blood spills into the area around the brain, which is filled with protective cerebrospinal fluid (CSF). This causes the brain to be surrounded by blood-contaminated CSF. While there are no warning signs for a subarachnoid hemorrhage, symptoms could include a sudden severe headache often described by patients as the "worst headache of my life." At least 30% of subarachnoid hemorrhages lead to a condition called vasospasm, which occurs when blood vessels irritated by excess blood begin to spasm and narrow in size. This makes it difficult to supply the brain with enough blood to survive.
Transient ischemic attack. A transient ischemic attack (TIA), or “mini stroke”, can cause symptoms similar to a stroke, but they usually last only a few hours and are resolved within 24 hours. An example of a symptom shared by both stroke and TIA is visual abnormalities such as sudden vision loss. Since TIAs are short (ie, transient), they do not result in significant permanent brain damage (NICE 2008; NSA 2012d). However, history of TIA increases future stroke risk (Lager 2012,Easton 2009).
Silent stroke. Silent strokes lack overt stroke-like symptoms and commonly go unnoticed (Vermeer 2007). However, silent strokes typically cause lesions in the brain, which can be detected using imaging such as magnetic resonance imaging (MRI). These lesions, known as brain infarcts, are associated with age-dependent memory loss and reduced brain volume (Blum 2012). Studies suggest that silent stroke is a hidden epidemic among American’s, with up to 40% of people over age 70 exhibiting signs (Lim 2010). It is estimated that silent strokes are 5 times more common than symptomatic strokes (Wang 2013).
A silent stroke differs from a transient ischemic attack (TIA) in that TIA symptoms are detectable but usually only last a short time (NICE 2008). Silent strokes can be the result of minor hemorrhages, or they could be lacunar infarcts, in which a penetrating artery becomes occluded, resulting in lesions in the brain's white matter (Yatsu 2004; Norrving 2003). In a study of 2040 stroke-free subjects with an average age of 62, over 10% showed signs of silent stroke when examined by MRI, even though they were not aware of any symptoms (Das 2008).