In a 35-year-old woman with a sudden pulsatile occipital headache and two episodes of vomiting, normal oxygen saturation, pulse rate, and blood pressure, and a prior normal brain CT after a head injury months ago, what is the most likely diagnosis and appropriate treatment?

Urgent Evaluation for Subarachnoid Hemorrhage Required

This patient requires immediate non-contrast head CT followed by lumbar puncture if CT is negative, as she presents with classic features of aneurysmal subarachnoid hemorrhage (aSAH) that demands urgent exclusion to prevent catastrophic outcomes.

Clinical Reasoning

This 35-year-old woman presents with sudden-onset pulsatile occipital headache and vomiting—a presentation that raises serious concern for aSAH despite normal vital signs. The American Heart Association/American Stroke Association guidelines explicitly state that aSAH is a medical emergency frequently misdiagnosed, and a high level of suspicion should exist in patients with acute onset of severe headache 1.

Why This Could Be Subarachnoid Hemorrhage

The key concerning features include:

• Sudden onset headache: The hallmark of aSAH is sudden headache reaching maximal intensity, described as "worst headache of my life" in 80% of cases 1
• Pulsatile occipital location: While aSAH can present with variable headache patterns, occipital location is common
• Associated vomiting: Nausea/vomiting occurs in 77% of aSAH cases 1, 2
• "Sentinel headache" possibility: 10-43% of patients report warning headaches before major rupture, and these sentinel bleeds increase odds of early rebleeding 10-fold 1

Critical Pitfall: Normal Vital Signs Do Not Exclude aSAH

The fact that her SpO2, pulse, and blood pressure are normal does not rule out aSAH. Many patients with aSAH present with normal vital signs initially, and misdiagnosis occurs in approximately 12% of cases, leading to nearly 4-fold higher likelihood of death or disability 1.

The Prior Head Trauma Is a Red Herring

The weight-based fall months ago with normal CT at that time is not relevant to this acute presentation. This is a new, sudden-onset headache requiring fresh evaluation.

Diagnostic Algorithm

Step 1: Immediate Non-Contrast Head CT

• CT sensitivity in first 3 days after aSAH is close to 100%, declining after 5-7 days 1, 2
• The most common diagnostic error in aSAH is failure to obtain a non-contrast head CT 1

Step 2: If CT is Negative, Perform Lumbar Puncture

• Because CT sensitivity is not 100%, lumbar puncture must be performed if initial CT is negative 1, 2
• Look for xanthochromia and elevated red blood cell count
• Guidelines state: "Acute diagnostic workup should include noncontrast head CT, which, if nondiagnostic, should be followed by lumbar puncture" 1

Step 3: If Both Negative, Consider Vascular Imaging

• If high clinical suspicion persists despite negative CT and LP, consider CT angiography or MR angiography
• In 1.4% of cases, aSAH is diagnosed only after vascular imaging despite normal CT and CSF 1

Alternative Diagnoses to Consider (After Excluding aSAH)

If aSAH is definitively ruled out, consider:

1. Reversible Cerebral Vasoconstriction Syndrome (RCVS): Can present with thunderclap headache and vomiting, though typically recurrent 3, 4
2. Cerebral Venous Thrombosis: Can cause sudden headache with vomiting, often with occipital location 5
3. Migraine: While possible, the sudden onset and severity warrant exclusion of life-threatening causes first

Treatment Approach

Before Diagnosis is Established:

• Blood pressure control with titratable agents to balance rebleeding risk and cerebral perfusion 1
• Antiemetics for symptomatic relief
• Do NOT give NSAIDs or aggressive analgesics until aSAH is excluded (bleeding risk)

If aSAH is Confirmed:

• Urgent neurosurgical/endovascular consultation
• Nimodipine 60mg every 4 hours (improves neurological outcomes) 1
• Early aneurysm obliteration (clipping or coiling) to prevent rebleeding 1
• Transfer to high-volume center if current facility performs <10 aSAH cases/year 1

If aSAH is Excluded and Migraine is Diagnosed:

• Combination therapy: NSAID (ibuprofen 400-800mg or naproxen 500-1000mg) plus acetaminophen 1000mg 6
• Add triptan (sumatriptan 50-100mg) if NSAIDs alone insufficient 6
• Antiemetic (metoclopramide 10mg or prochlorperazine) for nausea 7

Critical Time-Sensitive Points

• Rebleeding risk is 3-4% in first 24 hours after initial aSAH, with highest risk in first 2-12 hours 2
• 12% of aSAH patients die before receiving medical attention 1
• Misdiagnosis leads to 4-fold increased mortality/disability 1

Bottom line: This patient needs emergency department evaluation with urgent CT head NOW. The combination of sudden-onset headache with vomiting cannot be dismissed as simple migraine or food-related illness until life-threatening causes are excluded.