In a 55-year-old woman with a sudden, worst-of-her-life headache of three-hour duration, neck pain, and a normal physical examination, what is the appropriate initial diagnostic test?

Non-Contrast Head CT is the Appropriate Initial Test

In this 55-year-old woman presenting with sudden-onset worst headache of her life and neck pain, you should immediately order a non-contrast head CT as the first-line diagnostic test. 1, 2

Why Non-Contrast CT First

• This patient meets multiple Ottawa SAH Rule criteria (age ≥40 years and neck pain/stiffness), mandating workup for subarachnoid hemorrhage (SAH) regardless of a normal physical examination 1, 2
• Non-contrast head CT is the mandatory first imaging study for all patients with thunderclap or sudden severe headache because it is specifically optimized to detect hyperdense blood in the subarachnoid space 2
• Administering IV contrast during initial imaging is contraindicated because it masks the hyperdensity of acute blood and reduces diagnostic accuracy for SAH 2

Timing-Dependent Sensitivity

• When performed within 6 hours of symptom onset and interpreted by qualified neuroradiologists, non-contrast CT achieves 98.7% sensitivity for detecting SAH, missing fewer than 1.5 cases per 1,000 scans 1, 2, 3
• This patient presented 3 hours after onset, placing her well within the optimal diagnostic window 1
• After 6 hours, CT sensitivity declines substantially (≤90%) as blood products are reabsorbed, requiring additional testing 1, 3

Next Steps Based on CT Results

If CT is positive for SAH:

• Proceed immediately to CT angiography (CTA) with contrast to identify the bleeding source (aneurysm) and guide neurosurgical intervention 2

If CT is negative at 3 hours:

• Given the presentation within 6 hours and high-quality CT interpretation, the negative scan may be sufficient to exclude SAH in lower-risk scenarios 1, 2
• However, because this patient meets Ottawa SAH Rule criteria with neck pain, you should strongly consider lumbar puncture (LP) performed ≥6-12 hours after symptom onset for spectrophotometric xanthochromia analysis (sensitivity 100%, specificity 95.2%) 1, 3
• Alternatively, CTA can be performed as the next step if LP is contraindicated or refused 1

Critical Pitfalls to Avoid

• Never order CT angiography or MRI/MRA as the initial test—these are not designed to detect subarachnoid blood and will delay diagnosis 2
• Do not rely solely on physical examination; SAH can present with entirely normal neurological findings, and failure to identify SAH carries significant morbidity and mortality 1, 4
• Do not skip workup based on "normal exam"—the Ottawa SAH Rule exists precisely because physical examination alone is insufficient (specificity only 13.6-15.3%) 1, 3
• If CT is performed beyond 6 hours or is non-diagnostic, LP for xanthochromia is mandatory in high-suspicion cases 1, 2

Why Other Options Are Wrong

• CT angiography does not directly evaluate for SAH, only cerebrovascular pathology, and has reduced sensitivity (61%) for small ruptured aneurysms <3mm 1
• MRI/MRA takes too long and is not the standard first-line test for acute SAH 4, 5
• No test is inappropriate given that this patient meets multiple high-risk criteria and SAH carries 10-25% prevalence in thunderclap headache presentations 2