What are the key differences between traumatic and aneurysmal subarachnoid hemorrhage (SAH) in terms of clinical presentation, computed tomography (CT) scan findings, and management?

Differentiating Traumatic vs Aneurysmal Subarachnoid Hemorrhage

CT Scan Distribution Patterns

The most critical distinguishing feature on CT is the distribution pattern of blood: aneurysmal SAH typically shows blood concentrated in the basal cisterns and Sylvian fissures, while traumatic SAH predominantly involves the cerebral convexities and sulci. 1

Aneurysmal SAH CT Characteristics:

• Blood concentrated in basal cisterns (interpeduncular, suprasellar, ambient cisterns) 1
• Dense blood in Sylvian fissures (particularly if unilateral, suggests middle cerebral artery aneurysm) 1
• Blood often fills the third and lateral ventricles 2
• Fisher Grade IV pattern (diffuse thick cisternal blood with intraventricular extension) 3
• Blood persists on CT for 4-7 days, with 76% still visible on day 4 4

Traumatic SAH CT Characteristics:

• Blood predominantly over cerebral convexities (superficial cortical sulci) 1, 5
• Thin, scattered distribution along brain surface 4
• Rapidly clears from CT - only 2% visible by day 3 4
• Associated findings: skull fractures, contusions, subdural/epidural hematomas 5, 3
• Rarely involves basal cisterns unless major vessel injury 5, 3

Clinical Presentation Differences

Aneurysmal SAH:

• "Worst headache of life" - sudden, severe, maximal at onset 1
• Sentinel headache in 15-37% of cases days to weeks before major rupture 1
• Loss of consciousness at onset in majority of cases 1
• Seizures in up to 20% (first 24 hours, associated with intracerebral hemorrhage) 1, 6
• Meningismus common 1
• No history of trauma 1

Traumatic SAH:

• Clear history of head trauma with mechanism of injury 7, 5, 8
• Facial/scalp abrasions, bruising, or lacerations 5
• Headache less dramatic, proportional to trauma severity 7
• Altered consciousness related to diffuse brain injury, not hemorrhage alone 4

Critical Diagnostic Pitfall

Even with clear trauma history, basal cisternal SAH pattern mandates vascular imaging to exclude aneurysmal rupture, as aneurysms can rupture during or immediately before trauma. 7, 5, 8 CT angiography may be falsely negative in 10-14% of small aneurysms, requiring digital subtraction angiography for definitive exclusion 1, 8

When to Pursue Angiography in Trauma Patients

Absolute Indications:

• Basal cisternal or Sylvian fissure predominant blood despite trauma history 5, 3
• No skull fracture or contusion to explain SAH location 7
• Disproportionate amount of SAH relative to trauma severity 8
• Unilateral or focal SAH pattern 8

Imaging Algorithm:

1. CT angiography first (rapid, widely available) 1
2. Digital subtraction angiography if:
   • CTA shows aneurysm or vascular abnormality 5
   • Basal SAH pattern with negative CTA 1, 8
   • Delayed rebleeding occurs 8
3. Repeat angiography in 1-6 weeks if initial studies negative but suspicion remains high 1

Management Differences

Aneurysmal SAH:

• Immediate transfer to high-volume center (>35 cases/year) 6
• Nimodipine 60 mg every 4 hours for 21 days (reduces delayed cerebral ischemia) 6
• Early aneurysm securing within 24-72 hours (prevents rebleeding) 6
• Endovascular coiling preferred over clipping when feasible 6
• Aggressive monitoring for delayed cerebral ischemia days 4-14 1, 6

Traumatic SAH:

• Conservative management in most cases 5, 3
• No role for nimodipine (vasospasm rare and clinically insignificant) 4
• No aneurysm repair needed 3
• Focus on managing associated traumatic brain injury 4
• CSF diversion only if hydrocephalus develops 3

Key Pathophysiologic Differences

• Cerebral blood flow: In aneurysmal SAH, CBF drops to 65-75% and remains low; in traumatic SAH, CBF varies widely and often normalizes in subacute phase 4
• Vasospasm: Clinically significant in aneurysmal SAH (30-40%); rare and inconsequential in traumatic SAH 4
• Delayed ischemic deficits: Common in aneurysmal SAH; virtually absent in traumatic SAH 4
• Hydrocephalus: In aneurysmal SAH, 30% develop communicating hydrocephalus requiring shunt; in traumatic SAH, ventricular enlargement is from atrophy, not requiring shunt 4

Outcome Considerations

Traumatic SAH has significantly worse outcomes than aneurysmal SAH when matched for hemorrhage severity, due to associated diffuse brain injury rather than the SAH itself. 4 The SAH is a marker of injury severity but does not independently cause delayed complications as in aneurysmal cases 4.