A subdural hematoma is a collection of blood that accumulates between the brain and its outermost protective covering (the dura mater), caused by rupture of bridging veins that span this space. It can be acute — developing rapidly after significant trauma — or chronic — accumulating slowly over weeks after a minor or even unremembered injury. Both forms can cause life-threatening brain compression if not recognized and treated promptly.
Subdural hematomas are a critical diagnosis in patients presenting with neurological deterioration after head trauma, and must be distinguished from other causes of acute neurological decline including stroke and brain aneurysm rupture. The chronic form is particularly important to recognize in older patients with brain atrophy, in whom the stretched bridging veins are vulnerable to trivial trauma and who may present with symptoms mimicking dementia or stroke.
Causes
Head trauma
The most common cause of acute subdural hematoma is significant head trauma — motor vehicle accidents, falls, assaults, or sports injuries — that tears bridging veins or lacerates the brain surface. Rapid deceleration injuries are particularly high-risk because the brain continues moving inside the skull after impact, maximally stressing the bridging veins. This same mechanism underlies traumatic brain injury, and the two conditions frequently coexist.
Chronic and spontaneous causes
Chronic subdural hematomas most commonly affect older adults, in whom age-related brain atrophy stretches the bridging veins over a greater distance — making them vulnerable to tearing from minor or even trivial head impacts that would cause no injury in a younger person. Patients on anticoagulants (warfarin, direct oral anticoagulants) or antiplatelet agents (aspirin, clopidogrel) are at substantially increased risk of both developing a subdural hematoma and of hematoma expansion once bleeding begins. Chronic alcoholism, thrombocytopenia, and coagulation disorders are additional predisposing factors.
Symptoms
Acute subdural hematoma presents with rapidly progressive neurological decline following significant head trauma:
- Severe headache and altered consciousness — ranging from confusion to coma
- Unilateral weakness or paralysis (hemiparesis) on the side opposite the hematoma
- Unequal pupils (anisocoria) — a sign of dangerous transtentorial brain herniation requiring emergency intervention
- Seizures
Chronic subdural hematoma develops insidiously, often without a clear history of trauma, and is frequently misdiagnosed:
- Progressive headaches, often worse in the morning
- Cognitive decline, confusion, or personality changes — easily mistaken for dementia
- Gait instability and falls — which may themselves cause further subdural accumulation
- Fluctuating weakness or speech difficulty — mimicking stroke
- Symptoms may wax and wane as the hematoma enlarges, partially liquefies, and re-bleeds
Diagnosis
CT scan is the first-line emergency imaging study, rapidly identifying the hematoma as a crescent-shaped collection along the inner surface of the skull. CT density changes reliably with time: acute blood (0–3 days) appears bright white (hyperdense) due to clotted blood; subacute blood (3 days–3 weeks) becomes isodense with brain — the most dangerous phase, as it can be nearly invisible on CT without careful attention to subtle mass effect; chronic blood (over 3 weeks) appears dark (hypodense) as it liquefies.
MRI is significantly more sensitive than CT for subacute and chronic subdural collections, particularly isodense collections that are easily missed on CT. MRI also characterizes the underlying brain — identifying atrophy, contusions, diffuse axonal injury, and other pathology contributing to the clinical picture. In patients with unexplained cognitive decline or gait instability, MRI is the preferred study to exclude a chronic subdural hematoma that CT may underestimate or miss.
Classification
Subdural hematomas are classified by time course, which correlates with CT appearance and guides management:
- Acute (0–3 days): Hyperdense on CT. Typically from significant trauma. Often requires emergency surgical evacuation when causing neurological compromise.
- Subacute (3 days–3 weeks): Isodense on CT — the most easily missed phase. MRI is essential when clinical suspicion remains despite a normal or equivocal CT. Mass effect on the brain may be the only CT clue.
- Chronic (greater than 3 weeks): Hypodense on CT. Often presents insidiously in older patients. Surgical drainage through burr holes is well tolerated and highly effective.
Treatments
Treatment depends on hematoma size, rate of accumulation, degree of brain compression, neurological status, and the patient's overall health and anticoagulation status.
Conservative management:
Small, asymptomatic chronic subdural hematomas in neurologically intact patients may be observed with serial imaging and close clinical follow-up. Discontinuation or reversal of anticoagulant and antiplatelet medications — when medically safe — is an essential component of conservative management. Corticosteroids (dexamethasone) may reduce the inflammatory membrane surrounding chronic subdural collections and decrease recurrence risk in selected patients.
Surgical drainage:
Symptomatic or enlarging subdural hematomas require surgical evacuation. Chronic subdural hematomas are efficiently drained through burr holes — one or two small openings in the skull — under local or general anesthesia, with the liquefied blood washed out. Recurrence following burr hole drainage occurs in up to 20% of cases and may require repeat drainage or placement of a subdural drain left in situ for several days. Acute subdural hematomas causing significant brain compression, neurological deterioration, or herniation require emergency craniotomy for rapid and complete evacuation — a surgical emergency with outcomes directly tied to speed of intervention.
Anticoagulation reversal:
In patients on warfarin, direct oral anticoagulants, or antiplatelet agents, urgent reversal of anticoagulation is a critical priority to stop ongoing bleeding and allow clot stabilization. Specific reversal agents (vitamin K, prothrombin complex concentrate, idarucizumab for dabigatran, andexanet alfa for factor Xa inhibitors) are administered based on the anticoagulant involved. Resumption of anticoagulation after hematoma resolution requires careful individualized risk-benefit assessment.
Get an MRI to Confirm Your Diagnosis
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