What is the diagnostic approach for a patient suspected of having a cerebral aneurysm, presenting with a sudden, severe headache?

Diagnostic Approach for Suspected Cerebral Aneurysm

For patients presenting with sudden, severe headache suspicious for cerebral aneurysm rupture, immediately obtain a noncontrast head CT, and if negative, proceed with lumbar puncture to evaluate for xanthochromia—this sequential approach is the standard of care to prevent the devastating consequences of missed subarachnoid hemorrhage. 1

Initial Clinical Assessment

Maintain a high index of suspicion for aneurysmal subarachnoid hemorrhage (aSAH) in any patient with acute onset severe headache, as misdiagnosis occurs in up to 12% of cases and carries nearly 4-fold higher mortality and disability. 2 The classic presentation is described as "worst headache of my life" by 80% of patients who can provide history, reaching maximal intensity within 1 hour. 1, 2

Critical red flags requiring immediate workup include: 1, 2

• Sudden onset headache reaching maximum intensity within 1 hour
• Associated neck pain or stiffness
• Witnessed loss of consciousness
• Age ≥40 years (per Ottawa SAH Rule)
• Focal neurological deficits or cranial nerve palsies
• Altered mental status

Warning (sentinel) headaches occur in 10-43% of patients within 2-8 weeks before major rupture—recognizing these can be lifesaving. 1, 2

Diagnostic Algorithm Based on Timing

Patients Presenting >6 Hours from Symptom Onset OR With New Neurological Deficit

Step 1: Noncontrast Head CT 1

• CT has 98-100% sensitivity in the first 12 hours after hemorrhage 3
• Sensitivity decreases with time from symptom onset
• Look for blood in subarachnoid spaces, intracerebral hemorrhage, intraventricular hemorrhage, or hydrocephalus

Step 2: If CT is Negative, Perform Lumbar Puncture 1

• LP should be performed >6-12 hours after symptom onset for optimal xanthochromia detection 1
• Spectrophotometric analysis for xanthochromia has 100% sensitivity and 95.2% specificity 1
• This step is mandatory when clinical suspicion remains high despite negative CT

Patients Presenting <6 Hours from Symptom Onset WITHOUT New Neurological Deficit

A noncontrast head CT performed on a high-quality scanner and interpreted by a board-certified neuroradiologist is reasonable to diagnose or exclude aSAH without requiring LP. 1 However, if any doubt exists or the scanner/interpretation quality is uncertain, proceed with LP if CT is negative. 1

Vascular Imaging to Identify the Aneurysm

After Confirming Subarachnoid Hemorrhage

Step 1: CT Angiography (CTA) 3, 4

• Proceed immediately with CTA, which has 96.5-97.2% sensitivity and 88-97.9% specificity for detecting aneurysms 3, 4
• Modern multidetector CT (16- or 64-row) has significantly higher accuracy than single-detector CT 4
• Critical limitation: CTA has only 61% sensitivity for aneurysms <3mm 1

Step 2: Digital Subtraction Angiography (DSA) with 3D Rotational Angiography 1

• DSA is indicated when: 1
  • CTA is negative or inconclusive but SAH is confirmed
  • Diffuse SAH pattern suggests aneurysmal source
  • Treatment planning requires detailed vascular anatomy
• DSA has >98% sensitivity and specificity for detecting aneurysms 3
• DSA remains the gold standard for planning endovascular or surgical treatment 1

For Incidental Aneurysms (No Hemorrhage)

When an aneurysm is discovered incidentally during imaging for unrelated reasons (trauma, migraine, seizures, neoplasm staging), the diagnostic approach differs: 1, 2

• CTA or MR angiography may be sufficient for initial characterization
• DSA is reserved for treatment planning if intervention is considered
• The causality between unruptured aneurysms and chronic headache patterns remains unclear 2

Common Diagnostic Pitfalls to Avoid

Failure to obtain neuroimaging is the most common diagnostic error. 2 Never dismiss severe headache without appropriate workup, even if the patient appears well or symptoms have improved. 1

Do not skip lumbar puncture when CT is negative but clinical suspicion remains high. 1 The consequences of missed aSAH include rebleeding with 70-90% mortality. 3

Do not rely solely on CTA for small aneurysms. 1 If CTA is negative but SAH pattern is diffuse or clinical suspicion is high, proceed with DSA. 1

Recognize that even ruptured aneurysms can present with mild symptoms (Hunt and Hess Grade 1), so do not be falsely reassured by minimal symptoms if the headache pattern is concerning. 1, 2

Grading Clinical Severity

Rapidly assess clinical severity using validated scales, as this is the most useful indicator of outcome: 1

• Hunt and Hess Scale or World Federation of Neurological Surgeons (WFNS) Scale
• Grade ranges from 1 (mild headache, GCS 15) to 5 (coma, GCS 3-6)
• Higher grades correlate with worse outcomes and guide treatment decisions 1

Urgent Next Steps After Diagnosis

Once aSAH is confirmed, immediate actions include: 1, 3

• Transfer to high-volume center (>35 aSAH cases/year) with neurosurgical and endovascular capabilities
• Control blood pressure with titratable agents (target systolic <160 mmHg)
• Administer oral nimodipine 60 mg every 4 hours
• Secure the aneurysm within 24 hours to prevent rebleeding