Understanding The Causes Of Ischemic Stroke

An ischemic stroke occurs when there is a blockage in the blood vessels supplying blood to the brain, cutting off the blood supply and killing brain cells. This accounts for about 80-87% of all strokes. The main cause of ischemic stroke is atherosclerosis, or fatty deposits (plaque) that line the vessel walls, causing two types of obstruction: cerebral thrombosis and cerebral embolism. Cerebral thrombosis is a thrombus (blood clot) that develops at the site of fatty plaque within a blood vessel that supplies blood to the brain. Cerebral embolism is a blood clot that forms in the heart or large arteries of the upper chest or neck and then travels to the brain. Treatment for an ischemic stroke focuses on restoring blood flow to the brain, either through medication or mechanical procedures, and preventing further strokes.

Blocked blood vessels in the brain

Atherosclerosis, or fatty deposits (plaques) lining the vessel walls, is the main cause of ischemic strokes. These fatty deposits can lead to two types of obstruction: cerebral thrombosis and cerebral embolism. Cerebral thrombosis occurs when a blood clot, or thrombus, develops at the site of a fatty plaque within a blood vessel supplying blood to the brain. Cerebral embolism, on the other hand, is when a blood clot forms in the heart, large arteries of the upper chest or neck, or elsewhere in the circulatory system. A major cause of embolism is atrial fibrillation, an irregular heartbeat that can cause clots to form in the heart, dislodge, and travel to the brain.

The middle cerebral artery is the artery most commonly blocked during a stroke. The symptoms of an ischemic stroke include one-sided weakness or paralysis, aphasia (difficulty speaking), slurred speech, loss of muscle control on one side of the face, sudden loss of senses, blurred or double vision, loss of coordination, dizziness, nausea, emotional instability, confusion, memory loss, and severe headaches.

Treatment for ischemic strokes focuses on restoring blood flow to the affected areas of the brain as quickly as possible. This can be done through medication, such as thrombolytic drugs, or mechanical treatments like mechanical thrombectomy, where a catheter is used to remove the clot. Other treatments include mild hypothermia, blood sugar management, blood thinners, and oxygen therapy.

The key to minimising the damage caused by an ischemic stroke is speed; recognising the signs and seeking immediate medical attention are crucial.

Blood clots

An ischemic stroke occurs when a vessel supplying blood to the brain is blocked, cutting off blood supply to part of the brain and killing brain cells. This type of stroke accounts for about 87% of all strokes.

The main cause of ischemic stroke is atherosclerosis, or fatty deposits (plaque) that line the vessel walls. Fatty deposits can cause two types of obstruction:

Cerebral Thrombosis

This is a thrombus (blood clot) that develops at the site of a fatty plaque within a blood vessel that supplies blood to the brain.

Cerebral Embolism

This is a blood clot that forms in the heart or large arteries of the upper chest or neck, or another location in the circulatory system. Part of the blood clot breaks loose, enters the bloodstream, and travels through the brain's blood vessels until it reaches vessels too small to let it pass. A main cause of embolism is an irregular heartbeat called atrial fibrillation, which can cause clots to form in the heart, dislodge, and travel to the brain.

Treatment for Blood Clots

The urgent treatment for ischemic stroke is clot removal, which can be done through medication and mechanical treatments. Tissue plasminogen activator, r-tPA, (known as alteplase) is a medication approved by the Food and Drug Administration to treat ischemic stroke. Doctors administer alteplase through an IV in the arm, dissolving the clot and improving blood flow to the affected part of the brain. Mechanical treatments include thrombectomy procedures, where doctors use a wire-cage device called a stent retriever to remove the clot.

Atherosclerosis

The disease typically affects large and medium-sized arteries and is often caused by damage to the inner lining of an artery (the endothelium). This damage can be a result of physical stress, such as high blood pressure, high blood cholesterol, high blood sugar, or inflammation driven by the immune system. The fatty deposits, or plaque, that line the vessel walls can cause two types of obstruction: cerebral thrombosis and cerebral embolism.

Cerebral thrombosis is a blood clot that develops at the site of fatty plaque within a blood vessel supplying blood to the brain. On the other hand, cerebral embolism occurs when a blood clot forms in the heart, large arteries of the upper chest or neck, or elsewhere in the circulatory system. If a clot breaks loose, it can enter the bloodstream and travel to the brain, causing a blockage in the small vessels there.

The risk factors for atherosclerosis include male gender, family history of premature cardiovascular disease, high blood pressure, high blood cholesterol and triglycerides, cigarette smoking, exposure to tobacco smoke, unhealthy eating habits, and older age.

Cerebral thrombosis

Risk Factors and Causes

• Thrombophilia: A tendency to form blood clots due to abnormalities in coagulation, such as factor V Leiden mutation, protein C or protein S deficiency, antithrombin deficiency, or hyperhomocysteinemia.
• Nephrotic syndrome: A kidney disorder that causes protein loss in urine.
• Chronic inflammatory diseases: Conditions like inflammatory bowel disease, systemic lupus erythematosus, and Behçet's disease can increase the risk.
• Pregnancy and postpartum: The period before and after giving birth is associated with an increased risk of cerebral thrombosis.
• Hormonal contraception: The use of estrogen-containing hormonal contraceptives has been linked to a higher risk.
• Infections: Infections in the head and neck region, such as meningitis, sinusitis, otitis, and mastoiditis, can contribute to the development of cerebral thrombosis.
• Head injury and neurosurgery: Previous head trauma or neurosurgical procedures can be risk factors.
• Dehydration: Dehydration, particularly in infants and children, can be a factor in the development of cerebral thrombosis.
• Obesity: Obesity, especially when combined with oral contraceptive use, can increase the risk.

Symptoms and Diagnosis

• Severe headache: This is the most common symptom, affecting about 90% of patients. The headache typically worsens over several days and may be accompanied by nausea.
• Weakness or impaired control: Individuals may experience weakness or impaired control on one side of the body, affecting the face or limbs.
• Visual symptoms: Blurred or double vision, temporary loss of vision, and other visual disturbances can occur.
• Seizures: About 40% of patients experience seizures, which are more common in women with peripartum sinus thrombosis.
• Speech difficulties: Some individuals may have trouble speaking or understanding language.
• Altered mental status: In the elderly, changes in mental status and decreased consciousness may be observed.

The diagnosis of cerebral thrombosis is typically confirmed through computed tomography (CT) scans or magnetic resonance imaging (MRI) to demonstrate obstruction of the venous sinuses. These imaging techniques can visualise the veins and venous sinuses and detect the presence of blood clots.

Treatment

The treatment for cerebral thrombosis focuses on several aspects:

• Anticoagulants: Medications like low-molecular-weight heparin are used to suppress blood clotting and prevent new clots from forming.
• Thrombolysis: In some cases, enzymatic destruction of the blood clot (thrombolysis) may be used, but this approach is less common due to limited evidence.
• Thrombectomy: Mechanical thrombectomy is a surgical procedure to remove the blood clot and restore blood flow.
• Intracranial pressure management: Raised intracranial pressure may require interventions such as the placement of a shunt or neurosurgical treatments.
• Seizure management: Anticonvulsant medications may be used to prevent or treat seizures associated with cerebral thrombosis.
• Rehabilitation: Long-term recovery may involve rehabilitation to address any persistent symptoms or impairments.

Prognosis

Cerebral embolism

Causes

Other causes of cerebral embolism include:

• Fat globules entering the bloodstream after a bone fracture
• Tumour cells arising from atrial myxomata
• Gas embolism
• Atherosclerosis, or fatty deposits (plaque) that line the vessel walls

Symptoms

The most common symptoms of a stroke are:

• Drooping on one side of the face
• Arm weakness or numbness
• Difficulty speaking or understanding speech

Other possible symptoms include:

• Numbness or weakness in the face, arm, or leg, particularly on one side
• Dizziness or vertigo
• Loss of vision in one or both eyes
• Disorientation, confusion, or memory problems

Diagnosis

To diagnose a cerebral embolism, a doctor will first examine a patient's symptoms and review their medical history. To confirm the stroke and determine its cause, a doctor may use the following imaging and tests:

• CT scan to show the blood vessels in detail
• MRI to detect damaged brain tissue
• Carotid ultrasound to view blood flow and detect any fatty deposits in the carotid arteries
• Cerebral angiogram to establish a detailed view of the arteries in the neck and brain
• Echocardiogram to determine the location of any blood clots that may have travelled from the heart to the brain
• Blood tests to inform the treatment plan

Treatment

The urgent treatment for cerebral embolism is clot removal. Doctors can accomplish this with medication and mechanical treatments. The most effective treatment for stroke is a thrombolytic drug known as a tissue plasminogen activator (tPA), which helps break up blood clots. However, this drug is most effective if administered within 3 hours of symptom onset.

A mechanical thrombectomy involves inserting a catheter into an artery, often in the groin, and using a small clot-removing device to pull or suck out the clot.

Frequently asked questions