A stroke is a neurological disorder characterized by blockage of blood vessels. There are three major types of strokes; ischemic, hemorrhagic, and transient. Ischemic strokes, the most common type, occur when there is a blockage in blood flow to the brain causing brain damage and neuron death. Ischemic occlusions contribute to around 85% of casualties in stroke patients, with the remainder due to intracerebral bleeding. A hemorrhagic stroke leads to bleeding into and around the brain. Transient strokes occur when blood flow to the brain is briefly blocked.
The blood flow to the brain is managed by two internal carotids anteriorly and two vertebral arteries posteriorly (the circle of Willis). Clots form in the brain and interrupt blood flow, clogging arteries and causing blood vessels to break, leading to bleeding. Rupture of the arteries leading to the brain during stroke results in the sudden death of brain cells due to a lack of oxygen. Necrosis is followed by disruption of the plasma membrane, organelle swelling and leaking of cellular contents into extracellular space.
Other key events contributing to stroke pathology are inflammation, energy failure, loss of homeostasis, acidosis, increased intracellular calcium levels, excitotoxicity, free radical-mediated toxicity, cytokine-mediated cytotoxicity, complement activation, impairment of the blood–brain barrier, activation of glial cells, oxidative stress and infiltration of leukocytes. The dying brain tissue and resulting inflammation can form scar tissue, known as a glial scar.
Hypertension, hyperlipidemia, and the resulting atherosclerosis is a major risk factor of a stroke. In atherosclerosis, the blood flow is affected by narrowing of vessels. The build-up of plaque will eventually constrict the vascular chamber and form clots, causing a thrombotic stroke. Other risk factors include genetics, smoking, alcohol and drug abuse, physical inactivity, diet, and diabetes.
Depending on the region of brain damage, symptoms may include weakness, numbness, stiffness and difficulty of movement on one side of the body. Patients may also have problems with speech, memory, perception, vision, emotions, urination, and bowel movements.
The types and degrees of disability that follow a stroke depend upon which area of the brain is damaged. Generally, stroke can cause five types of disabilities including paralysis and motor control issues, sensory disturbances, aphasia (problem understanding language), problems with thinking and memory, and emotional disturbances. These can lead to patients experiencing symptoms of weakness, lack of coordination, problems walking, loss of sensation, problems with hand grasp, visual loss, or trouble speaking or understanding.