What are the causes of subacute subdural hematoma (SDH)?

Causes of Subacute Subdural Hematoma

Subacute subdural hematomas (saSDHs) are most commonly caused by minor head trauma in elderly patients, particularly those with cerebral atrophy, coagulopathy, or on antiplatelet/anticoagulant medications, with expansion typically occurring around 13 days post-injury. 1

Definition and Timeline

• Subacute subdural hematoma: Blood collection between the dura and arachnoid membranes that develops 4-21 days after head trauma 1
• Distinguished from:
  • Acute SDH: <4 days after trauma
  • Chronic SDH: >21 days after trauma

Primary Causes

Traumatic Causes

• Minor head trauma (most common cause, especially in elderly)
  • Often insignificant or forgotten trauma
  • Falls with low-impact head injury
• Acceleration-deceleration injuries causing tearing of bridging veins

Non-Traumatic/Spontaneous Causes

1. Vascular Abnormalities

   • Ruptured intracranial aneurysms 2, 3
     • Posterior cerebral artery aneurysms
     • Posterior communicating artery aneurysms
   • Arteriovenous malformations

2. Coagulopathy

   • Antiplatelet therapy (present in 52% of cases) 1
   • Anticoagulant use
   • Inherited bleeding disorders

3. Spontaneous Intracranial Hypotension

   • CSF leaks causing brain sagging and tearing of bridging veins 4

Risk Factors

Patient Demographics

• Advanced age (≥60 years) - 69.6% of cases 1
• Male gender (64% of cases) 1

Medical Conditions

• Cerebral atrophy (creates potential space for hematoma formation) 5
• Alcoholism 5
• Dementia 5
• Diabetes 5
• Seizure disorders 5
• Previous CSF shunts 5

Medications

• Anticoagulant therapy 5, 1
• Antiplatelet agents including aspirin 5, 1

Pathophysiology of Expansion

• Initial bleeding creates inflammatory response
• Formation of highly vascularized membrane around hematoma
• Repeated microbleeds from fragile vessels in membrane
• Osmotic gradient drawing fluid into hematoma space
• Impaired reabsorption of blood products

Clinical Presentation

• Progressive neurological deterioration after initial trauma
• Decline in Glasgow Coma Scale (average drop from 13 to 11) 1
• Headache
• Personality changes
• Speech difficulties
• Urinary incontinence 5
• Facial weakness (in some cases) 6

Diagnostic Approach

• CT head without contrast is first-line imaging for acute evaluation 4, 6
• MRI brain provides additional information in subacute cases 6
• CT angiography should be considered if vascular injury or aneurysm is suspected 6

Management Considerations

• Surgical intervention indicated for:
  • Thickness >5mm with midline shift >5mm
  • Significant mass effect causing neurological deterioration
  • Progressive neurological symptoms 6
• Treatment options:
  • Burr hole evacuation with closed-system drainage (most common) 1
  • Subdural peritoneal shunt placement (for recurrent cases) 5
  • Craniotomy with hematoma removal (less common) 1

Prognosis

• Mortality for subacute/chronic SDH: 13% at 30 days, 16.3% at 60 days, 19.7% at 100 days 7
• Better prognosis compared to acute SDH (25.1% mortality at 30 days) 7
• Early intervention may improve outcomes 6
• Poor prognostic factors:
  • Low admission Glasgow Coma Scale score
  • Age >80 years
  • Large hematoma volume (>50 cm³)
  • Associated contusions (>10 cm³)
  • Antiplatelet use 7

Pitfalls to Avoid

• Failing to consider aneurysmal rupture in spontaneous SDH without history of trauma
• Missing subtle neurological deterioration in elderly patients
• Overlooking medication history (anticoagulants/antiplatelets)
• Delaying treatment when expansion and neurological deterioration occur