A stroke is when blood flow to a part of your brain is stopped either by a blockage or the rupture of a blood vessel. The medical term for this is Cerebrovascular accident. As the definition states, it can be caused by one of two problems. Either by blockage of flow to an artery in the brain (ischemic stroke) or by a weakened blood vessel that ruptures (hemorrhagic stroke). Unlike 20 years ago when strokes were mostly treated by supportive care and physical therapy, there are now more definitive therapies.
Hemorrhagic stroke: This happens when a weakened blood vessel ruptures.This can be because of two reasons: a small aneurysm ( a weakened and thinned bulging portion of a vessel) or an arterio-venous malformation (AVM). These can rupture or bleed in someone with high uncontrolled blood pressure. The blood accumulates and compresses the surrounding brain tissue. The two types of hemorrhagic strokes are intracerebral (within the brain) hemorrhage or subarachnoid hemorrhage. These may require a neurosurgical intervention.
An arteriovenous malformation (AVM) is a cluster of abnormally formed blood vessels. Any one of these vessels can rupture, also causing bleeding into the brain. An aneurysm is a ballooning of a weakened region of a blood vessel. If left untreated, the aneurysm continues to weaken until it ruptures and bleeds into the brain.
Ischemic Stroke: Occurs when a vessel supplying blood to the brain is obstructed. This causes 87% of strokes. Since these are caused by blockage, these can sometimes be unblocked. Patients coming early enough can either get a clot breaking drug r-tPA, or in some institutions can be taken to a neuro radiology suite and have a catheter inserted into the carotid artery and advanced into the brain to have the clot directly broken up or aspirated. Patients coming to the emergency room are sent for an immediate CT scan to make sure there is no bleeding. Ischemic strokes can be of four types.
Thrombosis: A blood clot forms in a plaque in a blood vessel supplying a major or small portion of the brain. Similar to the heart, where the size of the vessel blocked determines the size of the brain infarct (how much damage is seen on CT scan or MRI). However, unlike the heart, the extent of clinical manifestation (amount of neurological deficit) can vary. A small infarct in one location can cause weakness of one half of the body, while a larger infarct in another area may only minor sensory defects.
Embolism: Cerebral embolism is a blood clot that forms at another location in the circulatory system, usually the heart and large arteries of the upper chest and neck. 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. It can cause clots to form in the heart, dislodge and travel to the brain.
Silent Infarct: Silent cerebral infarction (SCI), or “silent stroke,” is a brain injury likely caused by a blood clot that interrupts blood flow in the brain. It’s a risk factor for future strokes and a sign of progressive brain damage.
TIA: A Transient Ischemic Attack (TIA) is often called a mini-stroke, but it’s really a major warning. TIA is a temporary blockage of blood flow to the brain. Since it doesn’t cause permanent damage, it’s often ignored. But this is a big mistake. TIAs may signal a full-blown stroke ahead.
Cryptogenic Stroke: Cryptogenic stroke (CS) is defined as cerebral ischemia of obscure or unknown origin. The cause of CS remains undetermined because the event is transitory or reversible, investigations did not look for all possible causes, or because some causes truly remain unknown. One third of the ischemic strokes is cryptogenic. The reason this is important is because some of these causes if found can be prevented. I will discuss how this can be investigated in detail in the next issue.