Subdural Hematoma (SDH)

Definition & Anatomy

A subdural hematoma is a collection of blood in the potential space between the dura mater and the arachnoid membrane, caused by tearing of bridging veins that traverse the subdural space carrying venous blood from the cerebral cortex to the dural sinuses.

Pathophysiology

Mechanism: Sudden acceleration-deceleration forces shear the bridging dural veins → venous bleeding into the subdural space
Blood accumulates slowly (venous, low pressure) — unlike the arterial bleeding of epidural hematoma
Frequently associated with concurrent brain parenchymal damage (contusions, diffuse axonal injury)
Acute SDH may also result from: anticoagulant use, aneurysm rupture into the subdural space (rare), or non-accidental trauma in infants

Risk Groups

Group	Reason
Elderly	Cerebral atrophy → longer, more mobile bridging veins
Chronic alcoholics	Atrophic brain + coagulopathy
Anticoagulant users	Continued venous leakage, failure to tamponade
Infants <2 years	Thin skull, large head-to-neck ratio
Hemodialysis patients	Heparinization + uremic platelet dysfunction

Classification

Acute SDH (onset within 14 days of injury)

Usually follows severe trauma; patient often presents in coma
Associated with underlying cerebral contusions and edema
Surgical emergency — early evacuation improves outcome
Mortality remains significant due to underlying brain damage

Subacute SDH (days 4–14)

Isodense on CT; harder to identify — may require IV contrast or MRI

Chronic SDH (>14 days)

Common in elderly, alcoholics, anticoagulated patients
Often follows trivial or unrecalled trauma
A membrane forms around the hematoma; friable neovascularization leads to re-bleeding
Osmotic expansion: breakdown products draw in water → enlarging mass

Clinical Features

Headache (majority, but not universal)
Fluctuating level of consciousness — hallmark, can mimic metabolic encephalopathy or TIA
Tenderness to skull percussion at the hematoma site
Focal signs in 15–30%: hemiparesis, seizures, visual field defects
Unusual features: parkinsonism, dystonia, asterixis
Bilateral in ~20%; occasional interhemispheric location → bilateral leg weakness

A useful clinical rule: "It could always be a subdural" — imaging is required even without focal signs in any comatose patient. — Plum and Posner's Diagnosis and Treatment of Stupor and Coma

CT Imaging

Stage	CT Appearance
Acute	Hyperdense (white), crescent-shaped, crosses suture lines
Subacute	Isodense — easily missed
Chronic	Hypodense (dark) — iron has been metabolized

Chronic SDH CT (labeled):

Chronic subdural hematoma CT showing lateral ventricles shifted and the hypodense subdural collection

Chronic (low-density) SDH with midline shift — lateral ventricles displaced. (Gray's Anatomy for Students)

Acute SDH CT:

Small acute SDH right frontotemporal region — hyperdense crescent. (Tintinalli's Emergency Medicine)

Management

Type	Management
Acute/subacute	Surgical evacuation (craniotomy) — high mortality, higher need for surgery
Chronic	May be managed conservatively if small/minimally symptomatic; burr-hole drainage for larger collections
Anticoagulated	Reverse anticoagulation promptly
Corticosteroids	Reduce vasogenic edema from the hematoma membrane; can rapidly reverse symptoms in chronic SDH

Sources: Tintinalli's Emergency Medicine, A Comprehensive Study | Plum and Posner's Diagnosis and Treatment of Stupor and Coma | Gray's Anatomy for Students

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