Ischemic vs Hemorrhagic Stroke
Comparing Mechanisms, Neuroimaging Findings, and Acute Management
Introduction
Stroke refers to temporary reduction or interruption of the normal blood flow to the brain when a blood vessel ruptures or is blocked by a clot. More than 795,000 Americans experience a stroke each year, and of these, nearly 1 in 4 occur in people who have had a prior stroke. Strokes are classified into two categories, ischemic and hemorrhagic. Ischemic strokes are caused by a blockage in a blood vessel supplying the brain. Hemorrhagic strokes are caused by bleeding into and/or around the brain. The two categories share important similarities and differences in the risk factors, causes, and treatments.
Ischemic Stroke
Roughly 87% of strokes are classified as ischemic strokes. An ischemic stroke occurs when a blood clot blocks blood flow to a part of the brain. The clot may form in the brain’s arteries or travel from another part of the body, such as the heart. The initial emergency phase of an ischemic stroke is known as an Acute Ischemic Stroke (AIS).
An AIS is caused by either a thrombotic or embolic event that prevents or impairs blood flow to a region of the brain. A thrombotic event, or thrombosis, occurs when locally formed blood clots block blood vessels. An embolic event, or embolism, occurs when blood clots travel from elsewhere in the body to block blood vessels.
Pathophysiology: “Ischemic” means a reduction in blood flow that leads to a shortage of oxygen and essential nutrients. An ischemic stroke unfolds into a progressive cascade of events that involves depletion of energy stores and oxygen in the neurons, or nerve cells which leads to breakdown of the cell membrane, and ultimately cell death. As this process unfolds, brain tissue becomes damaged and eventually dies. Timely interventions can be made to salvage the damaged tissue by restoring blood flow prior to cell death.
Hemorrhagic Stroke
Accounting for 10%-15% of strokes globally and the highest rate of stroke mortality, hemorrhagic stroke results from bleeding into the brain tissue or the subarachnoid space, as a result of blood vessel rupture, trauma, or anticoagulation (blood thinner) related clotting problems. Hemorrhagic stroke can be divided into two types: intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH). ICH is bleeding into the brain parenchyma (the functional, active tissue of the brain), and SAH is bleeding into the subarachnoid space (the area of the brain responsible for holding cerebrospinal fluid). Half of all deaths involving hemorrhagic stroke occur within the first 48 hours, and thus early treatment is crucial for survival.
A hemorrhagic stroke can be caused by hypertension, or high blood pressure, which weakens blood vessels over time. Another common cause is a condition called cerebral amyloid angiopathy, which involves the accumulation of proteins in various structures of the brain, which increases risk of ICH in older individuals.
Pathophysiology: Hemorrhage means excessive or uncontrolled bleeding. When hemorrhage occurs in the brain, the blood forms a mass (hematoma) that displaces and compresses the brain’s functional tissue. This mass increases intracranial pressure and compromises blood flow. In an ICH, the blood flows directly into the brain tissue, while in a SAH, the blood flows into the space surrounding the brain, thereby compressing the brain. The hematoma initiates a cascade of events, leading to the accumulation of toxic cellular wastes and cellular breakdown. As blood flow is uncontrolled, cells swell and have disrupted electrolyte regulation, resulting in the accumulation of excess calcium which eventually leads to cell death.
Clinical Presentation
Distinguishing strokes as ischemic or hemorrhagic cannot be done just through clinical presentation, and is often accompanied through other methods, such as neuroimaging scans. To spot the signs of a stroke, an acronym called BE FAST can be used. This tool detects common signs of a possible stroke, including:
B - Balance loss, or instability when moving
E - Eyesight or vision changes, such as blurry vision or loss of vision
F - Face drooping
A - Arm weakness, or any sudden weakness in the body
S - Speech difficulty, such as slurring, garbled or nonsensical speech
T - Time to call 911
This tool can be implemented by trained medical professionals as well as bystanders. If any of the signs are noted, emergency services or 911 should be called at once.
Medical Intervention during a Stroke
Medical intervention is emergent during a stroke. An emergency team will most likely do a physical exam, blood tests, and a CT scan to determine the type of stroke and decide on urgent intervention. Other more advanced tests may include an MRI, an ultrasound of the blood vessels in the neck (carotid ultrasound), a cerebral angiogram, and/or an echocardiogram (an ultrasound of the heart) to determine the possible source and extent of a stroke.
Neuroimaging Findings
Within 20 minutes of admitting the patient, a non-contrast CT scan of the head is recommended to exclude brain bleeding. An MRI may provide more detailed information about the brain.
Acute Management
After the stroke has been diagnosed as ischemic or hemorrhagic, emergency treatment can begin. The most important mantra of stroke treatment is “time is brain”, as the amount of injury to the brain is correlated to the duration of impaired blood flow or bleeding into or around the brain. Thus, early intervention is absolutely essential once a stroke is suspected.
To treat an ischemic stroke, blood flow must quickly be restored to the brain. This can be done through a process known as thrombolysis. Thrombolysis is a treatment that dissolves blood clots to restore blood flow. An IV medication can break up a clot if it is given within 4.5 hours from when the symptoms began. In some cases, doctors may perform a procedure called mechanical thrombectomy, in which a catheter is guided through a blood vessel to remove the clot and restore blood flow to the brain.
To treat a hemorrhagic stroke, physicians focus on controlling the bleeding and reducing the pressure in the brain caused by the excess fluid. Medicines to counteract blood-thinners, lower the pressure in the skull, lower blood pressure, and prevent spasms of the blood vessels and seizures, can also be given. If the area of bleeding is large, physicians may recommend surgery to remove the blood collection if it is compressing the brain.
Complications
Neurologic complications can affect patients after having a stroke. Many patients may have long lasting paralysis of certain limbs or facial muscles, slurred speech, or other neurologic deficits. Brain edema, the swelling of the brain after the stroke, can also occur. Brain edema is life- threatening and needs immediate intervention. Frequent seizures are also a neurologic complication, causing convulsions, twitching, and significant changes in mentation. Mental health may also deteriorate after a stroke, causing depression, which can cause patients to have increased fatigue.
Stroke Risk Factors and Prevention
Some risk factors, such as high blood pressure, smoking, diabetes, and diet can be controlled to lower risk of stroke. Others, such as age, race, and family history are not modifiable. Patients should seek a doctor’s guidance in creating their personalized plan for stroke prevention. Stroke risk can be reduced by eating healthy, exercising daily, and in some cases, taking medication. Preventing a stroke starts by changing daily habits. Making healthier choices can lead to longer, healthier lives with decreased risk of stroke.
Written by Sai Sahana Diwakar
Edited by Elizabeth Kiraly, MD
References
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