Is a head bleed after trauma more likely to be a subdural hemorrhage or a subarachnoid hemorrhage?

Head Bleeds After Trauma: Subdural vs Subarachnoid Hemorrhage

In traumatic head injuries, subdural hemorrhage is more common than subarachnoid hemorrhage, with subdural hematoma being the most frequently encountered intracranial abnormality following trauma. 1

Epidemiology and Pathophysiology

Traumatic brain injury is a leading cause of death worldwide, with uncontrolled bleeding contributing to 30-40% of trauma-related deaths 1. When examining the types of intracranial hemorrhage following trauma:

• Subdural hematoma (SDH): Most common traumatic intracranial abnormality

  • Results from tearing of bridging veins between the cerebral cortex and dural sinuses
  • Often seen in multiple locations (convexity, interhemispheric, posterior fossa) 1
  • More common in elderly patients due to brain atrophy and increased vessel vulnerability
  • Higher mortality rates (up to 66% in severe cases) 2

• Subarachnoid hemorrhage (SAH):

  • Less common as a primary traumatic finding
  • Often occurs in conjunction with other intracranial injuries
  • More commonly associated with cerebral contusions 3
  • When isolated, more frequently seen with non-traumatic causes (e.g., aneurysmal rupture)

Diagnostic Considerations

The American College of Surgeons recommends using a grading system to assess the extent of traumatic hemorrhage 1. Initial evaluation should include:

1. Non-contrast CT scan: First-line imaging for traumatic head injury

   • Immediately indicated for patients with skull fractures or clinical signs of intracranial injury 1
   • Can identify both SDH and SAH, but more sensitive for SDH

2. MRI: Consider in non-emergent settings or when CT is negative but clinical suspicion remains high

   • Superior for detecting small-volume extra-axial hemorrhage
   • Can provide additional diagnostic information in approximately 25% of patients compared to CT 1

Risk Factors for Progression

Several factors increase the risk of hemorrhage progression requiring surgical intervention:

• For subdural hematoma:

  • Initial hematoma volume (OR = 1.094) 3
  • Degree of midline shift ≥10 mm (OR = 1.433) 4, 3
  • Hematoma thickness ≥15 mm 4
  • Age >65 years 2, 4
  • Lower Glasgow Coma Scale scores 4

• For combined SDH and SAH:

  • Higher risk of venous thromboembolism complications 5
  • May require earlier thromboprophylaxis (within 48 hours) 5

Management Implications

The management approach differs based on the type of hemorrhage:

• Subdural hematoma:

  • Often requires surgical evacuation, especially with significant mass effect
  • Decompressive craniectomy may be associated with lower mortality compared to craniotomy in severe cases 4
  • Time from injury to operative evacuation should be minimized 1

• Subarachnoid hemorrhage:

  • Often managed conservatively unless associated with other lesions requiring intervention
  • In traumatic SAH, blood pressure should be maintained <160 mmHg while avoiding hypotension (systolic <110 mmHg) 1

Clinical Pitfalls and Caveats

1. Diagnostic confusion: Sometimes traumatic SAH can be confused with aneurysmal SAH with secondary trauma (from fall after loss of consciousness) 6

2. Combined injuries: The combination of subdural and subarachnoid hemorrhage is actually the most common pattern of intracranial bleeding following trauma 5

3. Delayed deterioration: Initially non-operative acute subdural hematomas can enlarge over time, requiring delayed surgical evacuation in up to 35% of cases 3

4. Coagulopathy considerations: Patients on antithrombotic medications require rapid reversal while limiting fluid volumes (e.g., using prothrombin complex concentrate rather than fresh frozen plasma) 1

In conclusion, when evaluating head bleeds after trauma, clinicians should maintain a higher index of suspicion for subdural hemorrhage, particularly in elderly patients or those with significant mechanism of injury, while recognizing that combined patterns of hemorrhage are common and require careful monitoring for progression.