How do you differentiate aneurysmal (non-traumatic) subarachnoid hemorrhage from traumatic subarachnoid hemorrhage in a patient?

Differentiating Aneurysmal from Traumatic Subarachnoid Hemorrhage

The key distinction is that aneurysmal SAH requires urgent vascular imaging to identify and secure a ruptured aneurysm, while traumatic SAH does not involve aneurysm rupture and focuses solely on preventing secondary brain injury. 1, 2

Clinical History and Mechanism

Establish the mechanism of injury first:

• Traumatic SAH occurs in the context of head trauma with a clear mechanism of injury (fall, motor vehicle collision, assault) 3
• Aneurysmal SAH presents spontaneously with sudden-onset severe headache ("thunderclap" headache reaching maximum intensity within 1 hour), often described as "worst headache of life" 1, 3
• Aneurysmal SAH may present with witnessed loss of consciousness, onset during exertion, or neck pain/stiffness 1
• The Ottawa SAH Rule can help identify high-risk features for aneurysmal SAH in alert patients with severe nontraumatic headache 1

CT Imaging Pattern

The distribution of blood on noncontrast head CT provides critical diagnostic clues:

• Aneurysmal SAH typically shows blood concentrated in the basal cisterns, particularly around the circle of Willis, with diffuse or anteriorly located blood patterns 1, 4
• Traumatic SAH more commonly shows blood over the cerebral convexities, in superficial sulci, and often accompanies other traumatic findings (contusions, subdural hematoma, skull fractures) 3
• Perimesencephalic pattern (blood confined to cisterns around the midbrain) suggests non-aneurysmal hemorrhage with excellent prognosis 4

Vascular Imaging Requirements

This is the most critical management distinction:

• For aneurysmal SAH: Digital subtraction angiography (DSA) is indicated when there is high concern for aneurysmal source and negative or inconclusive CT angiography 1
• For traumatic SAH: Do NOT pursue aneurysm obliteration, as traumatic SAH does not involve aneurysm rupture 2
• CT angiography has approximately 97.2% sensitivity for detecting aneurysms, but sensitivity drops to 61% for aneurysms <3mm 1
• In spontaneous SAH with high suspicion for aneurysmal source, vascular imaging must be performed even if initial studies are negative 1

Management Divergence

The treatment pathways differ fundamentally:

For Aneurysmal SAH:

• Secure the ruptured aneurysm as early as feasible (ideally within 24 hours) to prevent rebleeding, which is frequently fatal 1
• Transfer immediately to high-volume centers with both neurosurgical and neuroendovascular expertise 1
• Administer enteral nimodipine (60mg every 4 hours) to prevent delayed cerebral ischemia and improve functional outcomes 1
• For anterior circulation aneurysms amenable to both techniques, endovascular coiling is recommended over surgical clipping to improve 1-year functional outcomes 1

For Traumatic SAH:

• Do NOT administer nimodipine - the evidence supporting nimodipine applies specifically to aneurysmal SAH 5
• No aneurysm obliteration is required 5, 2
• Blood pressure management focuses solely on preventing secondary brain injury without concern for aneurysm rebleeding 5, 2

Blood Pressure Management Nuances

Both conditions require careful BP control but with different rationales:

• Aneurysmal SAH (unsecured aneurysm): Gradual BP reduction when severely hypertensive (>180-200 mmHg), but strictly avoid hypotension (MAP <65 mmHg) to prevent both rebleeding and cerebral ischemia 1
• Traumatic SAH: Control BP with titratable agents to prevent secondary brain injury, maintaining MAP >65 mmHg, without concern for aneurysm rupture 5, 2

Common Pitfalls to Avoid

• Do not assume all spontaneous SAH is aneurysmal - 15-20% of spontaneous SAH cases show no aneurysm on initial angiography 4
• Do not skip vascular imaging in unclear cases - missing an aneurysm has grave consequences including death and severe disability 1
• Do not delay aneurysm treatment beyond 24 hours when feasible, as rebleeding risk is highest early and outcomes worsen with delayed treatment 1
• Do not use phenytoin for seizure prophylaxis in either condition, as it is associated with excess morbidity and mortality 1, 5

Shared Management Elements

Both conditions require:

• Admission to neurocritical care unit with frequent neurological assessments using validated scales (Glasgow Coma Scale, Hunt-Hess, WFNS) 1, 5
• Urgent CSF diversion if acute symptomatic hydrocephalus develops 1, 5
• Maintain euvolemia (not hypervolemia, which may be harmful) 1, 5
• Standardized ICU care bundles when mechanical ventilation required 1, 5
• Venous thromboembolism prophylaxis once hemorrhage is stable 5
• Multidisciplinary rehabilitation planning with validated screening tools for physical, cognitive, and behavioral deficits 1, 5