What Is a Subdural Haematoma?

A subdural haematoma occurs when blood builds up in the space between the brain and one of its protective coverings. To understand this condition, it helps to know how the brain is protected. The brain sits inside the skull, cushioned by three layers of membranes called the meninges. The outermost layer, closest to the skull, is a tough, leather-like covering called the dura mater. Beneath it lies the arachnoid mater, and closest to the brain tissue is the pia mater. These layers work together to shield the delicate neural tissue from harm.^[1]

When blood collects between the dura mater and the arachnoid mater, it forms a subdural haematoma. This bleeding typically happens when small veins that bridge the space between these layers tear, often due to a blow to the head. As blood accumulates, it can press against the brain, reducing the space available for brain tissue and potentially causing serious damage. The active bleeding into this space is called a subdural hemorrhage, while the buildup of blood itself is the haematoma.^[3]

There are different types of subdural haematomas, classified by how quickly they develop. An acute subdural haematoma is the most dangerous type, with symptoms appearing within minutes to hours after injury. The bleeding happens rapidly, and pressure on the brain increases quickly. Without prompt treatment, this type can lead to loss of consciousness, paralysis, or death.^[1]

A subacute subdural haematoma develops more gradually, with symptoms appearing anywhere from hours to several weeks after the initial head injury. This type can occur alongside a concussion. The slower development gives more time for diagnosis, but medical attention is still urgent.^[1]

The third type is a chronic subdural haematoma, which is more common in people over 65 years old. The bleeding occurs very slowly, and symptoms may not appear for weeks or even months after a head injury. In many cases, the injury was so minor that the person doesn’t even remember it happening. Even a slight bump can cause this type of bleeding in older adults because their brains may have shrunk with age, making the bridging veins more fragile and prone to tearing.^[1]

Epidemiology

Subdural haematomas are not uncommon among people who experience head injuries. Research shows that approximately one in four people with head injuries will develop a subdural haematoma. This makes it the most common type of traumatic mass lesion inside the skull.^[1][8]

The condition affects different age groups in distinct patterns. Younger men are most likely to experience acute subdural haematomas, often from severe head injuries in car accidents, falls, or violent attacks. These individuals typically face more dramatic and rapid-onset symptoms.^[5]

Older adults, particularly those over 65, face a higher risk for chronic subdural haematomas. About one-third of all subdural haematomas occur in this age group. The risk increases with age because the brain naturally shrinks as people get older, creating a larger space between the brain and the skull. This stretches the bridging veins over a longer distance, making them more vulnerable to tearing even from minor bumps or falls.^[5][6]

In infants and young children, subdural haematomas are often associated with severe forms of child abuse, including what is commonly called shaken baby syndrome. The sudden, violent shaking or impact can cause the delicate bridging veins in a child’s brain to tear. Traumatic birth delivery and the use of devices to help extract the baby during delivery also account for many cases in newborns.^[3][5]

Causes

The most common cause of a subdural haematoma is head injury. When the head experiences sudden impact or rapid movement, the brain can shift inside the skull. This movement stretches and tears the small bridging veins that run between the dura mater and the brain surface. Once torn, these veins bleed into the subdural space, creating the haematoma.^[4]

Head injuries leading to subdural haematomas can happen in many ways. Car accidents are a frequent cause, particularly when the head hits the dashboard, steering wheel, or window. Falls, especially from heights or down stairs, are another major cause. Violent attacks where someone is struck on the head can also result in this type of bleeding. Even sports injuries, particularly in contact sports, can lead to subdural haematomas.^[2]

The mechanism of injury matters. Subdural haematomas most often result from shearing forces—when the head moves suddenly in one direction while the brain momentarily continues in another direction due to inertia. This creates stress on the bridging veins, causing them to stretch and tear. Both rotational forces (twisting movements) and linear forces (straight-line impacts) can produce these shearing injuries.^[6]

In some cases, subdural haematomas occur without any obvious injury. This is more common in older adults whose brains have naturally shrunk with age, creating more space for movement within the skull. In these individuals, even normal head movements or very minor bumps might be enough to tear a vein.^[4]

Another cause in some people is a decrease in cerebrospinal fluid pressure, which is the fluid that normally cushions the brain. When this pressure drops, the brain can sag slightly, putting tension on the bridging veins and making them more likely to rupture. This can happen after procedures like lumbar puncture (spinal tap) or in people with cerebrospinal fluid leaks.^[5][6]

Risk Factors

Several factors increase a person’s likelihood of developing a subdural haematoma. Age is one of the most significant risk factors. People over 50, and especially those over 65, face higher risk because their brains tend to shrink with aging. This shrinkage, called brain atrophy, enlarges the subdural space and increases the distance bridging veins must span. The longer these veins stretch, the more vulnerable they become to tearing, even from minor impacts.^[5][6]

Taking blood-thinning medications dramatically increases the risk of subdural haematoma. Medicines like warfarin, aspirin, and other anticoagulants or antiplatelet drugs prevent blood from clotting normally. When someone on these medications experiences even a small tear in a blood vessel, the bleeding can continue longer and accumulate more rapidly than it would otherwise. People with blood clotting disorders, such as haemophilia, also face elevated risk for the same reason.^[2][4]

Long-term excessive alcohol consumption is another important risk factor. People with alcohol use disorders often have evidence of brain atrophy similar to that seen in elderly people. The brain shrinkage creates the same vulnerability—stretched bridging veins that tear more easily. Additionally, alcohol can affect blood clotting and increase the likelihood of falls and head injuries.^[4][6]

People with certain medical conditions face higher risk. Those with dementia may have brain shrinkage that increases vulnerability. Individuals who have had previous brain surgery have scar tissue and altered anatomy that may make bleeding more likely. People with conditions that lower cerebrospinal fluid pressure, such as those with brain shunts or spinal fluid leaks, also have increased risk.^[6]

A history of repeated head injuries, such as those experienced by people who fall frequently or participate in certain sports, increases risk over time. Each injury creates the potential for bleeding, and repeated trauma can damage blood vessels and brain tissue, making future haematomas more likely.^[4]

Very young children, particularly infants, are at risk due to their developing anatomy and vulnerability to abusive head trauma. Their soft skulls can enlarge as blood collects, and their delicate veins are easily damaged by shaking or impact.^[1]

Symptoms

The symptoms of a subdural haematoma vary widely depending on how quickly the bleeding occurs and how much pressure builds up inside the skull. Some people experience symptoms immediately after a head injury, while others may not notice anything wrong for days, weeks, or even months.^[1]

Headache is one of the most common symptoms. The pain typically doesn’t go away with ordinary painkillers. In acute subdural haematomas, the headache is usually severe and persistent. In chronic cases, the headache may be milder but constant, gradually worsening over time.^[2]

Nausea and vomiting often accompany the headache. As pressure increases inside the skull, it can affect the parts of the brain that control these functions. The vomiting may happen repeatedly and isn’t related to eating or digestive problems.^[1]

Confusion and memory problems are common, especially in chronic subdural haematomas. A person might seem disoriented, not knowing what day it is or where they are. They may forget recent conversations or events. In older adults, these symptoms are sometimes mistaken for dementia, stroke, or simply “old age,” which can delay proper diagnosis.^[2]

Personality changes may occur, making someone behave in unusual ways. A normally calm person might become unusually aggressive or irritable. Someone typically social might withdraw and lose interest in activities they once enjoyed. These changes happen because the pressure on the brain affects areas that control mood and behavior.^[2]

Physical symptoms often include drowsiness or increased sleepiness beyond normal tiredness. A person may have trouble staying awake or keeping their eyes open. Speech can become slurred, making it difficult to understand what they’re saying. They might also have trouble swallowing.^[2]

Vision problems are another warning sign. Some people experience blurred vision, where everything looks fuzzy or out of focus. Others see double, with two images where there should be one. These symptoms occur when pressure on the brain affects the nerves that control eye movements and vision.^[2]

Balance and coordination difficulties often develop. A person might become unsteady on their feet, have trouble walking in a straight line, or fall frequently. They may have difficulty with tasks requiring fine motor control, like buttoning a shirt or using utensils.^[2]

Weakness or numbness affecting one side of the body is a serious symptom. One arm or leg might feel weak or difficult to move. The face might droop on one side. This happens when the haematoma presses on the parts of the brain that control movement on the opposite side of the body.^[1]

As pressure continues to build, more severe symptoms can develop. These include complete paralysis, where a person cannot move parts of their body at all. Seizures may occur—sudden episodes of uncontrolled shaking or loss of consciousness. Breathing can become abnormal, either too fast, too slow, or irregular. Eventually, a person may lose consciousness completely or slip into a coma.^[1]

In infants, the symptoms look different. A baby with a subdural haematoma might have an enlarged head because the soft skull can expand as blood collects. The soft spots on the skull, called fontanelles, may bulge outward. The baby might cry more than usual with a high-pitched sound, have feeding problems, be unusually sleepy, or vomit repeatedly. Seizures can also occur in babies.^[1]

Sometimes, people have what’s called a “lucid interval.” This means they seem fine immediately after a head injury—talking normally and appearing alert—but then develop symptoms hours or days later. This pattern can be particularly dangerous because people assume they’re fine and delay seeking help.^[1][8]

Prevention

While accidents can happen unexpectedly, several measures can reduce the risk of head injuries that lead to subdural haematomas. Wearing appropriate protective equipment is one of the most effective prevention strategies. Anyone riding a bicycle or motorcycle should always wear a properly fitted helmet. These helmets are specifically designed to absorb impact and protect the skull and brain during falls or collisions.^[7]

In workplaces where head injuries are possible—such as construction sites, factories, or anywhere heavy objects might fall—wearing safety helmets and following all safety protocols is essential. Employers should provide proper equipment, and workers should use it consistently.^[7]

Fall prevention is particularly important for older adults, who face higher risk of subdural haematomas even from minor falls. Simple home modifications can make a significant difference. Removing tripping hazards like loose rugs, electrical cords, and clutter from walkways helps prevent falls. Installing grab bars in bathrooms, especially near toilets and in showers, provides stability. Ensuring good lighting throughout the home, particularly on stairs and in hallways, helps people see where they’re stepping. Non-slip mats in bathtubs and showers prevent slipping on wet surfaces.^[7]

For people taking blood-thinning medications, careful management is crucial. Anyone on anticoagulants or antiplatelet drugs should have regular check-ups to monitor their medication levels and discuss any concerns with their doctor. These individuals need to be especially careful about avoiding head injuries and should seek medical evaluation even after seemingly minor bumps to the head. However, it’s vital to continue taking prescribed blood thinners unless a doctor specifically advises stopping, as discontinuing these medications without guidance can cause serious complications like strokes or blood clots.^[7]

After experiencing any head injury or concussion, allowing proper rest and recovery time before returning to normal activities, especially sports or physically demanding work, helps prevent further injury. The brain needs time to heal, and rushing back to activities too quickly increases the risk of another, potentially more serious, injury.^[7]

Regular health check-ups become more important with age. Monitoring overall health, including vision and balance problems that might increase fall risk, helps identify issues before they lead to injuries.^[7]

Pathophysiology

Understanding what happens inside the skull when a subdural haematoma forms helps explain why this condition is so serious. The brain sits suspended within the skull, surrounded by the three protective layers of meninges. Between these layers, particularly in the subdural space between the dura and arachnoid, run small veins called bridging veins. These veins carry blood from the brain surface to larger vessels that drain into major veins leaving the skull.^[3]

When the head experiences sudden impact or rapid acceleration and deceleration, the brain can shift position inside the skull. The brain essentially has some room to move within its protective coverings. During this movement, the bridging veins that connect the brain to the dura mater become stretched. If the force is strong enough, or if the veins are already fragile due to age or other factors, they tear. Unlike arteries, which carry blood under high pressure and bleed rapidly, veins operate under lower pressure and bleed more slowly. This explains why subdural haematomas, especially chronic ones, can develop gradually over time.^[3][8]

Once a vein tears, blood begins leaking into the subdural space. In acute cases, the bleeding may be more rapid, quickly forming a collection of blood that presses against the brain. The skull is rigid and cannot expand, so as blood accumulates, it takes up space that the brain would normally occupy. This creates pressure on brain tissue, compressing it and potentially causing damage.^[4]

In chronic subdural haematomas, the process differs slightly. The initial bleeding may be small and slow. Over time, the blood that has collected begins to break down and changes consistency. Instead of remaining as clotted blood, it becomes more liquid. The body attempts to contain this blood by forming membranes around it. However, these membranes contain fragile new blood vessels that can leak, adding more blood to the collection. The breakdown products of old blood also draw water into the haematoma through a process called osmosis, causing it to slowly expand like a balloon filling with fluid.^[5]

As the haematoma grows, whether quickly or slowly, it continues taking up more space inside the fixed volume of the skull. The brain tissue gets pushed and compressed. This pressure doesn’t affect all parts of the brain equally—areas closer to the haematoma experience more pressure than distant areas. The pressure can also cause the brain to shift from its normal position, a process called midline shift because the structures that normally sit in the center of the head get pushed to one side.^[3]

When pressure inside the skull increases enough, it reduces blood flow to brain tissue. The brain requires constant oxygen and nutrients delivered by blood. When blood flow decreases, brain cells can become damaged or die. This is why symptoms develop—the affected brain regions can no longer function normally.^[4]

In the most severe cases, the pressure becomes so great that the brain begins to herniate. This means parts of the brain get pushed through or past normal anatomical boundaries inside the skull. Brain herniation is immediately life-threatening because it can compress the brainstem, which controls vital functions like breathing and heart rate. It can also squeeze the blood vessels supplying the brain, cutting off blood flow entirely.^[3]

In older adults and people with brain atrophy, the pathophysiology has unique features. The shrunken brain creates a larger subdural space filled with cerebrospinal fluid. The bridging veins must stretch across this enlarged space, making them more vulnerable to tearing from even minor trauma. Additionally, because there’s more space available before the brain gets compressed against the skull, these individuals may not develop symptoms until the haematoma becomes quite large.^[3]

In acute subdural haematomas, there’s often damage to the underlying brain tissue from the same injury that caused the bleeding. This is called primary brain injury. The blood collection itself creates secondary brain injury by compressing tissue and reducing blood flow. The combination of primary and secondary injury explains why acute subdural haematomas have such high rates of serious complications even with treatment.^[8]