- Acceleration-deceleration brain injury leading to tearing of bridging vessels. Blood collects in potential space between dura mater and arachnoid mater.
- Acute: ≤14 days; more severe than chronic; often associated with parenchymal brain injury; diagnosis with CT scan and treated with surgery
- Chronic: >2 weeks; often seemingly trivial injury in older patients, e.g., fall from standing; good prognosis after surgery; recurrence is common.
Predominant age (1):
- Acute: Predominant age group 30–50 years
- Chronic: Predominant age group >50 years
- Acute: 1–2 per 100,000 per year; male > female; acute subdural hematoma is present in 5–22% of episodes of severe head trauma.
- Chronic: 3.4 per 100,000 <65 years; 8–58 per 100,000 ≥65 years (prevalence is increasing with aging population)
As many as 1 in 2,000 patients from general population may have incidental subdural hemorrhage seen on MRI (2
- Acute: Severe head trauma (e.g., MVAs, falls, child abuse)
- Chronic: Cerebral atrophy, chronic alcoholism, dementia, falls, minor trauma, epilepsy, coagulopathy/anticoagulation therapy, antiplatelet drugs, low ICP, hemodialysis, child abuse (1)
Cerebral atrophy due to age or alcoholism predisposes to subdural hematomas. Never forget nonaccidental trauma in children!
- Acute: Seatbelt, bicycle/motorcycle helmet, construction hard hat
- Chronic: Alcoholism treatment, PT, epilepsy treatment, cautious prescription of anticoagulation therapy, shunts in hydrocephalus patients
- Bleed (e.g., from tearing of bridging veins; most common cause), injury to small cortical arteries (rare), low CSF pressure causing reduced brain buoyancy
- Fibroblasts proliferate, wall off hematoma, and migrate into hematoma.
- Bleeding usually is tamponaded by compression due to increasing ICP or direct compression by the clot itself
- Phagocytes cause liquefaction of the hematoma, which eventually resolves if the bleed is slow enough. If unable to reabsorb, it becomes chronic.
- Hematoma not entirely reabsorbed; alternatively, recurrent bleeding at least as fast as body's resorption rate. The membrane encapsulating the clot may calcify over time (1).
- Young adult: 56% MVAs; 12% falls
- Elderly: 22% MVAs; 56% falls
- Trauma from high-velocity acceleration-deceleration brain injury
- Blunt trauma often leads to subdural bleeds on coup side of brain as opposed to epidural bleeds, which tend to occur on contre-coup side.
- Geriatric patients: Trivial head injury (e.g., fall from standing)
- Children: May be caused by nonaccidental head trauma, unrecognized/unreported trauma, or, rarely, birth trauma
Both acute and chronic subdural bleeds can occur without physical impact!
Commonly Associated Conditions
- Acute: Brain contusion or subarachnoid hemorrhage (most common); epidural hematoma, diffuse axonal injury, facial fractures; cervical spine injury (1)
- Chronic: Subdural hygroma (extracranial collection of CSF), seizure disorder, coagulopathy, CSF shunt, birth trauma, child abuse, metastatic carcinoma (rare)
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