Brain bleeds happen when a blood vessel inside or around the brain ruptures, leaking blood into surrounding tissue. The most common cause is long-term high blood pressure, which gradually weakens the walls of small arteries until they give way. But several other conditions, injuries, and medications can also trigger bleeding, and the location of the rupture determines what type of brain bleed you’re dealing with and how dangerous it is.
Where Brain Bleeds Occur
Your brain is wrapped in several protective layers, and a bleed can start in any of them. The four main types are defined by location:
- Epidural bleed: between the skull bone and the outermost membrane (the dura mater), most often caused by trauma.
- Subdural bleed: between the dura mater and the next layer down (the arachnoid membrane), common in older adults and after head injuries.
- Subarachnoid bleed: between the arachnoid membrane and the innermost layer covering the brain, frequently caused by a ruptured aneurysm.
- Intracerebral hemorrhage: bleeding within the brain tissue itself, in any region including the deep structures and brainstem. This is the most common type of spontaneous brain bleed.
High Blood Pressure: The Leading Cause
Chronically elevated blood pressure is behind the majority of spontaneous brain bleeds. When blood pressure stays high for years, the constant pounding gradually damages the walls of small arteries deep inside the brain. These tiny vessels develop weak spots, lose their elasticity, and eventually rupture. The bleeding tends to occur in predictable deep-brain locations where those small arteries are under the most stress.
What makes this cause so significant is that it’s largely preventable. Many people with uncontrolled hypertension don’t feel sick, so the damage accumulates silently over decades before a vessel finally fails.
Aneurysms and Malformed Blood Vessels
Some people are born with, or develop, structural weak points in their brain’s blood vessels. The two most important ones are aneurysms and arteriovenous malformations (AVMs).
An aneurysm is a balloon-like bulge in an artery wall. Blood pools inside this sac, and the stretched wall can rupture without warning, flooding the space around the brain with blood (a subarachnoid hemorrhage). Many aneurysms never rupture, but when they do, the bleeding is sudden and severe.
AVMs are tangles of abnormal connections between arteries and veins that bypass the normal capillary network. Blood flows through these tangles at high pressure because there’s no capillary bed to slow it down. Several factors predict whether an AVM will bleed: a location deep in the brain, drainage through deep veins, and whether the AVM has bled before. A prior hemorrhage makes the risk of another bleed roughly five times higher.
Head Injuries and Physical Trauma
A blow to the head, a car accident, or a fall can cause brain bleeds even in people with perfectly healthy blood vessels. The mechanism is straightforward: when the brain is suddenly accelerated or decelerated, mechanical shearing forces stretch and tear small blood vessels and nerve fibers. This microvascular damage can produce anything from tiny scattered bleeds to large, life-threatening collections of blood pressing against the brain.
Trauma is the most common cause of epidural bleeds, which typically involve a torn artery right beneath a skull fracture. Subdural bleeds after trauma can develop slowly over days or weeks, especially in older adults whose brain has slightly shrunk away from the skull, leaving fragile veins more exposed to tearing.
Amyloid Buildup in Older Adults
In people over 65, a condition called cerebral amyloid angiopathy becomes an increasingly important cause of brain bleeds. Clumps of abnormal amyloid protein gradually accumulate along the inside walls of blood vessels in the brain. Over many years, these deposits weaken the vessel walls, creating microscopic cracks and fissures that let blood seep into the surrounding brain tissue.
The process is slow and progressive. Early on, the leaks are tiny and may cause no noticeable symptoms. Over time, as more protein accumulates and more damage occurs, larger amounts of blood escape and the symptoms worsen. Unlike hypertension-related bleeds, which tend to occur deep in the brain, amyloid-related bleeds typically happen closer to the brain’s surface in the outer lobes.
Blood Thinners and Medication Risk
Anticoagulant medications, commonly called blood thinners, increase the risk of brain bleeds because they reduce the blood’s ability to clot. In patients taking older-generation blood thinners like warfarin, the annual rate of intracranial hemorrhage is 0.3% to 0.6%. Newer blood thinners cut that risk roughly in half, with annual rates of 0.1% to 0.2%.
Those percentages sound small, but they add up over years of treatment, and they’re significantly higher than the risk in people not taking these medications. The tricky part is that blood thinners are prescribed for good reasons, usually to prevent strokes caused by clots. The decision to use them always involves weighing clot prevention against bleeding risk, and that balance shifts depending on your age, blood pressure control, and other factors.
Other Contributing Causes
Several additional factors can trigger or contribute to brain bleeds. Liver disease reduces the body’s ability to produce clotting factors, making bleeding more likely throughout the body, including the brain. Brain tumors can erode into blood vessels or develop their own fragile, abnormal blood supply that ruptures easily. Cocaine and amphetamine use can cause sudden, extreme spikes in blood pressure that overwhelm even healthy vessel walls.
Blood disorders that impair clotting, such as hemophilia or severely low platelet counts, also raise the risk. In rare cases, infections or inflammatory conditions can weaken vessel walls enough to cause bleeding.
Warning Signs of a Brain Bleed
The symptoms of a brain bleed depend on the location and size of the bleeding, but four hallmarks appear across most types: a sudden, severe headache (often described as the worst headache of your life), weakness or numbness on one side of the body, seizures, and a decreased level of consciousness that can range from confusion to complete unresponsiveness. These symptoms typically come on suddenly rather than building gradually.
A CT scan is the primary tool for rapid diagnosis. It can detect bleeding in the brain within minutes, which matters because treatment decisions need to happen fast. In-hospital mortality for intracerebral hemorrhage runs around 23%, making speed critical.
Risk of a Second Bleed
Once someone has had a brain bleed, the risk of it happening again doesn’t disappear. Recurrence rates are approximately 2% within the first year and close to 10% over five years. The risk is highest in people whose underlying cause hasn’t been addressed, particularly those with uncontrolled blood pressure or ongoing amyloid angiopathy.
Aggressive blood pressure management is the single most effective step for reducing the chance of recurrence. For people whose bleed was related to blood thinners, the decision about whether and when to restart those medications requires careful individual assessment of the competing risks of clotting and bleeding.