Neurology · PANCE / PANRE

Subdural Hematoma (SDH)

Bleeding between dura and arachnoid from torn bridging veins; crescent-shaped on CT.

Also known as: SDH, subdural hemorrhage, chronic subdural

Overview

Collection of blood in the potential space between the dura mater and the arachnoid mater, typically from rupture of bridging cortical veins as they cross to the dural sinuses. Classified as acute (<3 days), subacute (3 days-3 weeks), or chronic (>3 weeks) by appearance and timing.

Epidemiology

Most common in the elderly and chronic alcohol users due to cerebral atrophy stretching bridging veins. Also common in infants (suspect non-accidental trauma if no clear mechanism). Bilateral in ~15% of chronic cases.

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Risk factors

Advanced age (cerebral atrophy)
Chronic alcohol use (atrophy + coagulopathy)
Anticoagulant or antiplatelet therapy
Coagulopathy, thrombocytopenia
Falls in elderly (often unwitnessed and minor)
Cerebrospinal fluid hypotension (post-LP, post-shunt, spontaneous intracranial hypotension)
Recent head trauma (any severity)
Infant with suspected abusive head trauma (shaken baby — bilateral SDH + retinal hemorrhages)

Pathophysiology

Acceleration-deceleration forces tear bridging veins crossing the subdural space, allowing low-pressure venous blood to accumulate. In the elderly with atrophy, bridging veins are stretched and tear with minor trauma. Hematoma may stabilize (chronic SDH) or expand by repeated small bleeds from neomembranes — leading to delayed presentation weeks after the inciting injury.

Clinical presentation

Symptoms

Acute SDH: history of significant trauma, immediate decreased consciousness, headache, vomiting
Chronic SDH: insidious onset over weeks-months of headache, cognitive decline, mild hemiparesis, gait disturbance — often mistaken for dementia or stroke
Subacute SDH: intermediate course (days to weeks)
Elderly may have NO recalled trauma

Signs / physical exam

Variable depending on size and chronicity
Focal deficits: contralateral hemiparesis, aphasia, gaze deviation
Pupillary abnormalities (uncal herniation in large acute SDH)
In chronic SDH: subtle confusion, gait apraxia, mild hemiparesis
Signs of elevated ICP if large

Classic findings

Crescentic (concave/'moon-shaped') extra-axial collection on CT that crosses suture lines. Acute = hyperdense (white), subacute = isodense (may be subtle), chronic = hypodense (dark).

Differential diagnosis

Epidural hematoma — Lens-shaped (biconvex), respects suture lines, arterial source (middle meningeal artery), classic lucid interval, rapid deterioration
Intraparenchymal hemorrhage — Within brain substance, hypertensive deep bleeds or lobar amyloid bleeds
Cerebral atrophy with subdural hygroma — CSF density, no blood; common in elderly
Dementia / delirium — Mimics chronic SDH in elderly with cognitive decline; CT excludes
Stroke — Acute focal deficit; CT differentiates ischemic from hemorrhagic
Meningioma — Slow-growing, may cause similar cognitive/focal symptoms; contrast enhancement

Diagnostic workup

Labs

CBC, platelets, PT/INR, PTT — anticoagulation common in this population
BMP, LFTs
Type and screen if surgical intervention likely

Imaging

Non-contrast head CT — first-line, identifies acute SDH easily
Subacute (isodense) SDH may be missed on CT; contrast or MRI helpful
MRI — most sensitive for small or chronic SDH and dating the bleed
Repeat CT in 6-24 h if patient deteriorates or has progressive symptoms

Diagnostic algorithm

Feature	Subdural Hematoma	Epidural Hematoma
Source	Bridging veins (low pressure)	Middle meningeal artery (high pressure)
Shape on CT	Crescent (concave)	Lens / biconvex
Crosses suture lines	Yes	No
Crosses midline (dural reflections)	No	Yes
Onset / course	Variable — acute, subacute, or chronic	Rapid; classic lucid interval
Population	Elderly, alcoholics, anticoagulated	Young, after temporal blow

Subdural vs. epidural hematoma comparison.

Treatment

First-line

ABCs; intubate if GCS ≤8
Reverse anticoagulation: warfarin → 4-factor PCC + vitamin K 10 mg IV; DOACs → idarucizumab (dabigatran) or andexanet alfa / 4-factor PCC (factor Xa inhibitors); aspirin/clopidogrel — platelet transfusion controversial
BP control (avoid hypotension; target SBP <160 in acute SDH)
Manage ICP: head of bed 30°, normocapnia, hypertonic saline or mannitol if herniation signs
Seizure prophylaxis (short-course levetiracetam) commonly used in acute SDH

Acute SDH — Surgical

Craniotomy with hematoma evacuation if: thickness >10 mm, midline shift >5 mm, GCS deterioration, or pupil asymmetry
Best outcomes with surgery within 4 hours of deterioration

Acute SDH — Conservative

Small, thin, asymptomatic SDH: serial neuro exams, repeat CT, close monitoring in ICU

Chronic SDH

Burr hole drainage with subdural drain (preferred, lower morbidity than craniotomy)
Twist-drill craniostomy is an alternative
Middle meningeal artery embolization — emerging adjunct or alternative (EMBOLISE trial 2024)
Conservative management if asymptomatic and small

Second-line / adjunct

Discontinue antiplatelet/anticoagulant therapy and reassess risk-benefit
Address underlying coagulopathy and cause (fall prevention, alcohol cessation)
Avoid restarting anticoagulation prematurely after SDH (typical delay 4-8 weeks, individualized)

Complications

Cerebral edema and herniation
Recurrence (especially chronic SDH, ~10-20% after burr hole drainage)
Seizures (early or late)
Persistent cognitive deficits, dementia
Subdural empyema if infected
Surgical complications: bleeding, infection, tension pneumocephalus

PANCE pearls

Crescent shape and crossing of suture lines differentiates SDH from epidural hematoma on CT.
In elderly patient with insidious cognitive decline or new gait disorder — get a CT to rule out chronic SDH ('great masquerader of dementia').
Bilateral SDH may not produce midline shift but can still cause significant pressure — measure thickness, not just shift.
Subacute SDH (1-3 weeks) is isodense to brain on CT — easily missed; use MRI or contrast CT.
Infant SDH + retinal hemorrhages + no trauma history → suspect abusive head trauma.

References

Brain Trauma Foundation 2017 — Guidelines for the Management of Severe Traumatic Brain Injury (Carney et al., Neurosurgery 2017, 4th edition)
EMBOLISE Trial — Middle Meningeal Artery Embolization for Chronic Subdural Hematoma (Liu et al., NEJM 2024)
Surgical Guidelines — Surgical Management of Acute Subdural Hematomas (Bullock et al., Neurosurgery 2006)

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