What are the etiologies of subdural hemorrhage?

Causes of Subdural Hemorrhage

Subdural hemorrhage results from bleeding between the dura and arachnoid mater, most commonly caused by accidental trauma, but also arising from coagulopathy, non-accidental trauma, cranial surgery, vascular malformations, and ruptured intracranial aneurysms. 1

Primary Etiologic Categories

Traumatic Causes

Accidental trauma remains the most common cause of subdural hemorrhage across all age groups. 1

• Blunt head trauma with moderate to severe injury (GCS ≤13) carries high risk for subdural hemorrhage and requires immediate CT imaging 2
• Mild head trauma can produce subdural hemorrhage, particularly in patients with risk factors such as anticoagulation 3
• Birth-related subdural hemorrhage occurs in 33% of normal deliveries, predominantly in the posterior fossa, with highest incidence (63.3%) in assisted vaginal deliveries 4
  • These birth-related hemorrhages are asymptomatic, resolve by 25 days of age, and have no long-term sequelae 4
  • They must be distinguished from traumatic subdural hemorrhage occurring postnatally 4

Non-Accidental Trauma

Non-accidental trauma is a routinely encountered cause of subdural hemorrhage, particularly in pediatric populations. 1

• Suspected abusive head trauma requires specific imaging protocols distinct from accidental injury evaluation 2

Coagulopathy and Anticoagulation

Anticoagulation increases the risk of subdural hematoma expansion three-fold (26% vs 9% in non-anticoagulated patients). 3

• Patients on warfarin, direct oral anticoagulants, or antiplatelet agents require 24-hour observation with repeat CT at 20-24 hours after injury 3
• Coagulopathy represents a routinely encountered cause independent of trauma severity 1

Vascular Causes

Ruptured intracranial aneurysm is a rare but critical cause of subdural hemorrhage that may present without concurrent subarachnoid hemorrhage. 5

• This represents a neurosurgical emergency with treatment strategies differing from traumatic subdural hemorrhage 5
• Outcomes are poor if treatment is delayed, making early recognition essential 5
• Vascular imaging should be considered when subdural hemorrhage occurs without clear traumatic mechanism 5

Venous stroke with thrombosed cortical veins can produce subdural hemorrhage, particularly in infants 6

• Thrombosed cortical veins may leak blood into the subdural space, creating chronic subdural hemorrhage/hygroma 6
• This mechanism is associated with laminar subarachnoid hemorrhage in 24 of 34 cases reviewed 6

Iatrogenic Causes

Cranial surgery is a routinely encountered cause of subdural hemorrhage 1

• Post-surgical subdural collections may develop as expected complications of neurosurgical procedures 1

Chronic Subdural Hematoma Pathophysiology

Chronic subdural hematoma develops through a positive feedback loop of inflammation, angiogenesis, and persistent exudation of blood into the subdural space. 7

• The process begins with a first leak of blood from dural border cells after mild trauma 8
• Inflammatory cells are drawn to the border cell layer, forming new membranes from activated inflammation 8
• The hematoma enlarges through angiogenic factors and new capillary formation 8
• This inflammatory mechanism was historically described by Virchow in 1857 as "pachymeningitis hemorrhagica interna" 8

Critical Diagnostic Considerations

When to Suspect Non-Traumatic Etiology

When history or imaging evidence of trauma is absent, the differential diagnosis for subdural hemorrhage must be expanded beyond accidental trauma. 1

• Do not attribute neurological findings solely to pre-existing conditions without first excluding acute intracranial pathology using appropriate imaging 3
• Consider vascular imaging (CTA) when subdural hemorrhage presents without clear traumatic mechanism 5

Imaging Mimics to Avoid Misdiagnosis

Several entities closely mimic subdural hemorrhage on non-contrast CT scans, and overdiagnosis can lead to unnecessary hospital admissions or invasive procedures. 1

• Knowledge of pathologic, iatrogenic, anatomic/physiologic, and artifactual mimics is essential in emergency settings 1
• The laminar subarachnoid hemorrhage associated with venous stroke is commonly and incorrectly described as a mixed density or layered subdural hemorrhage 6

Secondary Complications

Herniation from subdural hemorrhage can cause compression of perforating arteries, resulting in infarcts of the anteromedial striatum and globus pallidus. 9

• Compression of the anterior choroidal artery and recurrent artery of Heubner produces this uncommon pattern of secondary ischemic injury 9
• Subacute injury (8 days to 1 month post-trauma) may result from secondary processes including herniation, ischemia, hydrocephalus, and progressive hemorrhage 2