Causes

Thrombotic Strokes 

In thrombotic strokes a thrombus usually forms around an atheromatous plaque. Blockage of the artery is usually gradual meaning onset is usually longer. Thrombotic strokes can be divided up into two categories depending on which vessel is affected; Large Vessel Disease and Small Vessel Disease.

Diseases that may form thrombi in the large vessels include: atherosclerosis, vasoconstriction (tightening of the artery), aortic, carotid or vertebral artery dissection.

Diseases that may form thrombi in the small vessels include: lipohyalinosis, (build-up of fatty hyaline matter in the blood vessel as a result of high blood pressure) fibrinoid degeneration and microatheroma (small atherosclerotic plaques).

Sickle cell anemia, which can cause blood cells to clump up and block blood vessels, can also lead to stroke. A stroke is the second leading killer of people under 20 who suffer from sickle-cell anemia.

Embolic Strokes

Embolic stroke are also most frequently due to a thrombus but it has travelled from elsewhere. However it could be due to a number of other substances including fat, air, cancer cells or bacteria debris. In an embolic stroke not only must the stroke be treated but the source of the embolism must be identified to prevent reoccurrence. 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 embolises through an atrial or ventricular septal defect in the heart into the brain.

Sickle cell image courtesy of Wikimedia Commons in the public domain and is thus free of any copyright licence.

Venous thrombosis

Cerebral venous sinus thrombosis leads to stroke due to locally increased venous pressure, which exceeds the pressure generated by the arteries. Infarcts are more likely to undergo haemorrhagic transformation (leaking of blood into the damaged area) than other types of ischemic stroke.

Intracerebral Haemorrhage

Intracerebral Haemorrhage occurs in small arteries or arterioles and is commonly due to hypertension, trauma, bleeding disorders, or vascular malformations. 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% after 30 days, higher than ischemic stroke and subarachnoid hemorrhage.