Thrombotic<unk>  Illustration of an embolic<unk> , showing a blockage lodged in a blood vessel. In thrombotic<unk> , a thrombus (blood clot) usually forms around atherosclerotic plaques. Since blockage of the artery is gradual, onset of symptomatic thrombotic<unk> s is slower than that of a hemorrhagic<unk> . A thrombus itself (even if it does not completely block the blood vessel) can lead to an embolic<unk>  (see below) if the thrombus breaks off and travels in the bloodstream, at which point it is called an embolus. Two types of thrombosis can cause<unk> : * Large vessel disease involves the common and internal carotid arteries, the vertebral artery, and the Circle of Willis. Diseases that may form thrombi in the large vessels include (in descending incidence): atherosclerosis, vasoconstriction (tightening of the artery), aortic, carotid or vertebral artery dissection, various inflammatory diseases of the blood vessel wall (Takayasu arteritis, giant cell arteritis, vasculitis), noninflammatory vasculopathy, Moyamoya disease and fibromuscular dysplasia. * Small vessel disease involves the smaller arteries inside the brain: branches of the circle of Willis, middle cerebral artery,<unk> em, and arteries arising from the distal vertebral and basilar artery. Diseases that may form thrombi in the small vessels include (in descending incidence): lipohyalinosis (build-up of fatty hyaline matter in the blood vessel as a result of high blood pressure and aging) and fibrinoid degeneration (a<unk>  involving these vessels is known as a lacunar<unk>  and microatheroma (small atherosclerotic plaques). Sickle-cell anemia, which can cause blood cells to clump up and block blood vessels, can also lead to<unk> . A<unk>  is the second leading cause of death in people under 20 with sickle-cell anemia. Air pollution may also increase<unk>  risk. Embolic<unk>  An embolic<unk>  refers to an arterial embolism (a blockage of an artery) by an embolus, a traveling particle or debris in the arterial bloodstream originating from elsewhere. An embolus is most frequently a thrombus, but it can also be a number of other substances including fat (e.g., from bone marrow in a broken bone), air, cancer cells or clumps of bacteria (usually from infectious endocarditis). Because an embolus arises from elsewhere, local therapy solves the problem only temporarily. Thus, the source of the embolus must be identified. Because the embolic blockage is sudden in onset, symptoms usually are maximal at the<unk> art. Also, symptoms may be transient as the embolus is partially resorbed and moves to a different location or dissipates altogether. Emboli most commonly arise from the heart (especially in atrial fibrillation) but may originate from elsewhere in the arterial tree. In paradoxical embolism, a deep vein thrombosis embolizes through an atrial or ventricular septal defect in the heart into the brain. Causes of<unk>  related to the heart can be distinguished between high and low-risk: * High risk: atrial fibrillation and paroxysmal atrial fibrillation, rheumatic disease of the mitral or aortic valve disease, artificial heart valves, known cardiac thrombus of the atrium or ventricle, sick sinus syndrome, sustained atrial flutter, recent myocardial infarction, chronic myocardial infarction together with ejection fraction <28 percent, symptomatic congestive heart failure with ejection fraction <30 percent, dilated cardiomyopathy, Libman-Sacks endocarditis, Marantic endocarditis, infective endocarditis, papillary fibroelastoma, left atrial myxoma and coronary artery bypass graft (CABG) surgery. * Low risk/potential: calcification of the annulus (ring) of the mitral valve, patent foramen ovale (PFO), atrial septal aneurysm, atrial septal aneurysm with patent foramen ovale, left ventricular aneurysm without thrombus, isolated left atrial "smoke" on echocardiography (no mitral<unk> enosis or atrial fibrillation), complex atheroma in the ascending aorta or proximal arch. Among those who have a complete blockage of one of the carotid arteries, the risk of<unk>  on that side is about one percent per year. A special form of embolic<unk>  is the embolic<unk>  of undetermined source (ESUS). This subset of cryptogenic<unk>  is defined as a non-lacunar brain infarct without proximal arterial<unk> enosis or cardioembolic sources. About one out of six ischemic<unk> s could be classified as ESUS. Cerebral hypoperfusion Cerebral hypoperfusion is the reduction of blood flow to all parts of the brain. The reduction could be to a particular part of the brain depending on the cause. It is most commonly due to heart failure from cardiac arrest or arrhythmias, or from reduced cardiac output as a result of myocardial infarction, pulmonary embolism, pericardial effusion, or bleeding. Hypoxemia (low blood oxygen content) may precipitate the hypoperfusion. Because the reduction in blood flow is global, all parts of the brain may be affected, especially vulnerable "watershed" areas—border zone regions supplied by the major cerebral arteries. A watershed<unk>  refers to the condition when the blood supply to these areas is compromised. Blood flow to these areas does not necessarily<unk> op, but instead it may lessen to the point where brain damage can occur. Venous thrombosis Cerebral venous sinus thrombosis leads to<unk>  due to locally increased venous pressure, which exceeds the pressure generated by the arteries. Infarcts are more likely to undergo hemorrhagic transformation (leaking of blood into the damaged area) than other types of ischemic<unk> . Intracerebral hemorrhage It generally occurs in small arteries or arterioles and is commonly due to hypertension, intracranial vascular malformations (including cavernous angiomas or arteriovenous malformations), cerebral amyloid angiopathy, or infarcts into which secondary hemorrhage has occurred. Other potential causes are trauma, bleeding disorders, amyloid angiopathy, illicit drug use (e.g., amphetamines or cocaine). The hematoma enlarges until pressure from surrounding tissue limits its growth, or until it decompresses by emptying into the ventricular system, CSF or the pial surface. A third of intracerebral bleed is into the brain's ventricles. ICH has a mortality rate of 44 percent after 30 days, higher than ischemic<unk>  or subarachnoid hemorrhage (which technically may also be classified as a type of<unk> . Other Other causes may include spasm of an artery. This may occur due to cocaine. Silent<unk>  A silent<unk>  is a<unk>  that does not have any outward symptoms, and people are typically unaware they have had a<unk> . Despite not causing identifiable symptoms, a silent<unk> <unk> ill damages the brain and places the person at increased risk for both transient ischemic attack and major<unk>  in the future. Conversely, those who have had a major<unk>  are also at risk of having silent<unk> s. In a broad<unk> udy in 1998, more than 11 million people were estimated to have experienced a<unk>  in the United<unk> ates. Approximately 770,000 of these<unk> s were symptomatic and 11 million were first-ever silent MRI infarcts or hemorrhages. Silent<unk> s typically cause lesions which are detected via the use of neuroimaging such as MRI. Silent<unk> s are estimated to occur at five times the rate of symptomatic<unk> s. The risk of silent<unk>  increases with age, but may also affect younger adults and children, especially those with acute anemia.
Stroke
Hypoglycemia
Epilepsy
Hypertensive encephalopathy
Subarachnoid hemorrhage
Giant cell arteritis
Migraine 
Bell's palsy