Brain bleeds happen when a blood vessel inside the skull ruptures or leaks, allowing blood to pool in or around the brain. Globally, about 29 cases per 100,000 people occur each year, and the causes range from physical trauma to conditions that silently weaken blood vessels over decades. Understanding these causes matters because brain bleeds are serious: roughly 35% of patients die within 30 days, and only about 15% are discharged home to live independently.
Head Trauma
Physical injury to the head is one of the most straightforward causes. The type and location of bleeding depend on the forces involved and which structures get damaged. A fracture of the bone at the temple can tear an artery running along the inside of the skull, causing blood to collect between the skull and the brain’s outer covering. This is called an epidural hematoma and can build pressure rapidly.
A different pattern occurs when the brain shifts inside the skull during an impact. Small veins that bridge the gap between the brain’s surface and its outer membrane can tear, producing a subdural hematoma. This type is especially common in older adults and people who take blood thinners, because even a minor fall can cause enough movement to rip those fragile veins. High-speed accidents involving sudden deceleration, like car crashes, can also cause bruise-like hemorrhages on the brain’s surface, typically at the front and sides of the brain where it strikes the inside of the skull.
Rotational forces, the kind that whip the head around rather than simply striking it, can stretch and shear deep brain tissue and its tiny blood vessels. This type of injury, called diffuse axonal injury, scatters small bleeds throughout the brain and is one of the most devastating forms of traumatic brain injury.
High Blood Pressure
Chronic high blood pressure is the single most common cause of spontaneous (non-traumatic) brain bleeds. Years of elevated pressure gradually damages the walls of small arteries deep inside the brain. These weakened vessels can eventually rupture without any external trigger. The bleeding typically occurs in areas supplied by small penetrating arteries, particularly deep brain structures involved in movement and sensation. Imaging after these bleeds often reveals signs of longstanding small vessel disease, including tiny prior bleeds and areas of white matter damage visible on MRI.
What makes hypertension so dangerous is that the damage accumulates silently. Many people have no symptoms until a vessel finally gives way. Controlling blood pressure is the single most effective way to reduce the risk of this type of brain bleed.
Brain Aneurysms
An aneurysm is a balloon-like bulge in a blood vessel wall. When one forms on an artery in the brain and ruptures, blood spills into the space surrounding the brain, causing what’s known as a subarachnoid hemorrhage. The hallmark symptom is a sudden, explosive headache often described as the worst of a person’s life.
Several factors increase the chance that an aneurysm will grow and eventually burst. Smoking, high blood pressure, having multiple aneurysms, a family history of brain aneurysms, and being female all raise the risk. Anatomically, larger aneurysms and those located on arteries toward the back of the brain (the posterior circulation) are more prone to rupture. An aneurysm that’s actively growing carries a rupture rate of about 3.1% per year, compared to just 0.1% per year for one that remains stable in size. Many small aneurysms never rupture and are sometimes found incidentally on brain scans done for other reasons.
Arteriovenous Malformations
An arteriovenous malformation, or AVM, is a tangle of abnormal blood vessels present from birth. Normally, blood flows from arteries through progressively smaller vessels and tiny capillaries before reaching veins. In an AVM, that network of small vessels is missing. Blood rushes directly from high-pressure arteries into thin-walled veins that aren’t built to handle that force.
Over time, the extreme pressure stretches and weakens the vessel walls. Bulges can form on the affected vessels, and the entire malformation can eventually rupture, bleeding into the surrounding brain tissue. AVMs can go undetected for years, sometimes causing no symptoms until a bleed occurs. They account for a small but significant share of brain hemorrhages, particularly in younger adults who don’t have the typical risk factors like high blood pressure or aging.
Blood-Thinning Medications
Anticoagulants and antiplatelet drugs, commonly prescribed for atrial fibrillation, blood clots, or after heart procedures, increase the risk of bleeding everywhere in the body, including the brain. The risk isn’t enormous for any single person, but across large populations it’s measurable and clinically significant. Newer anticoagulants like apixaban appear to carry a somewhat lower risk of brain bleeding compared to older options, though the risk is never zero.
The concern isn’t just that these medications can cause a brain bleed on their own. They also make any existing vulnerability worse. A small vessel weakened by high blood pressure or amyloid deposits (discussed below) that might have only leaked a tiny amount can produce a much larger, more dangerous hemorrhage in someone on blood thinners. About a third of in-hospital brain bleed deaths in population studies involve patients taking oral anticoagulants. If you take these medications, the benefits of preventing clots and strokes still outweigh the bleeding risk for most people, but the balance shifts depending on your individual risk factors.
Amyloid Buildup in Older Adults
Cerebral amyloid angiopathy, or CAA, is a condition where abnormal proteins gradually accumulate along the walls of blood vessels in the brain. Over many years, these protein deposits weaken the vessel walls and create microscopic cracks that let blood seep into surrounding brain tissue. CAA is strongly age-related and becomes increasingly common after age 60.
Unlike hypertension-related bleeds, which tend to occur deep in the brain, CAA-related bleeds typically happen near the brain’s surface in the outer lobar regions. Imaging often reveals a pattern of small prior bleeds scattered across the cortex, along with a distinctive surface staining from old blood. CAA can cause repeated small hemorrhages over time, each one potentially damaging cognition and function. There’s currently no way to clear the protein deposits, so management focuses on controlling other risk factors, particularly avoiding blood thinners when possible and keeping blood pressure in check.
Other Vascular Causes
Blood clots forming in the brain’s venous drainage system, known as cerebral venous thrombosis, can cause bleeding by backing up blood flow until pressure builds and vessels rupture. This is relatively rare but disproportionately affects younger women, particularly during pregnancy or while taking hormonal contraceptives.
Certain brain tumors, both cancerous and non-cancerous, can bleed as they grow. Tumors develop their own fragile, poorly formed blood vessels that are prone to rupture. A sudden hemorrhage is sometimes the first sign that a tumor exists. Infections that damage blood vessel walls, cocaine and amphetamine use (which can cause sudden spikes in blood pressure), and blood clotting disorders that impair the body’s ability to stop bleeding can all trigger brain hemorrhages as well.
Warning Signs of a Brain Bleed
Most people who experience a brain bleed describe a sudden, severe headache as the first symptom. Other signs include sudden weakness or numbness on one side of the body, slurred speech, confusion, nausea and vomiting, vision changes, difficulty with balance or coordination, and sensitivity to light. A stiff neck can indicate bleeding around the brain’s surface. In severe cases, seizures or loss of consciousness may follow.
These symptoms overlap with other types of stroke, and there’s no way to tell from symptoms alone whether a stroke involves bleeding or a blocked artery. A CT scan of the head is the standard first test because it can detect fresh blood within minutes. MRI provides additional detail and can identify the underlying cause, age the bleeding, and detect signs of prior small hemorrhages that might point toward conditions like CAA or small vessel disease. If an aneurysm or AVM is suspected, specialized imaging of the blood vessels helps pinpoint the source.
Why Some People Are at Higher Risk
Risk factors compound each other. An older adult with high blood pressure, early amyloid deposits in their blood vessels, and a prescription for blood thinners faces a meaningfully higher combined risk than any single factor would suggest. Smoking accelerates damage to blood vessel walls and promotes aneurysm growth. Heavy alcohol use raises blood pressure and impairs clotting. A family history of brain aneurysms or hemorrhagic stroke increases risk independently of lifestyle factors.
The most impactful modifiable risk factors are blood pressure control, not smoking, and limiting heavy alcohol use. For people with known aneurysms, regular monitoring with imaging can catch growth before a rupture occurs, and preventive treatment is sometimes an option for aneurysms that reach a concerning size or show signs of instability.