Lumbar Puncture is Required
Despite the patient's improved symptoms and desire to leave, lumbar puncture must be performed because the clinical presentation is classic for subarachnoid hemorrhage (SAH) and CT sensitivity is insufficient to rule out this life-threatening diagnosis. 1, 2
Why This Patient Cannot Be Discharged
This 41-year-old woman presents with the quintessential features of SAH that mandate further investigation:
- Sudden-onset severe headache ("thunderclap") triggered by physical exertion is the hallmark presentation of aneurysmal SAH 2
- Peak intensity during exertion significantly elevates SAH probability 3
- Age ≥40 years and exertional onset meet Ottawa SAH Rule criteria requiring investigation 3
- SAH carries >40% mortality within 30 days if untreated, with catastrophic consequences if missed 2
CT Limitations in This Clinical Context
While the noncontrast head CT is normal, this does not exclude SAH:
- CT sensitivity decreases significantly after 6 hours from symptom onset (93% at 24 hours, 57-85% at 6 days) 2, 3
- The patient presented "two hours" after onset, but the exact timing of the CT scan relative to symptom onset is not specified 2
- Even within 6 hours, CT misses 1-2% of SAH cases 3, 4
- Fourth-generation CT technology, while improved, still has limitations for detecting small bleeds 2
Guideline-Mandated Next Step: Lumbar Puncture
The American Heart Association explicitly recommends lumbar puncture when there is high clinical suspicion of SAH with a negative or non-conclusive CT scan. 1, 2
Key procedural considerations:
- Lumbar puncture should be performed at least 12 hours after headache onset for optimal xanthochromia detection 2, 4
- Xanthochromia (yellow CSF discoloration from bilirubin) is the key diagnostic finding, not just bloodstained CSF 2
- Spectrophotometric analysis has maximum sensitivity when performed 12 hours to 2 weeks after symptom onset 2
- LP has high diagnostic yield, eliminating need for neurosurgical investigation in almost 90% of cases when negative 5
Addressing the Timing Controversy
There is nuanced evidence about the "6-hour rule":
- If CT is performed within 6 hours AND interpreted by an experienced neuroradiologist, some guidelines suggest LP may not be necessary 2, 3, 6
- However, the Canadian Stroke Best Practice Recommendations state that when clinical suspicion remains high despite negative CT, lumbar puncture should be performed regardless of timing 2
- In this case, we don't know if a neuroradiologist interpreted the scan, and the clinical presentation is extremely high-risk 2
Why Other Options Are Incorrect
- CT angiogram (Option A) is premature—it's indicated after SAH is confirmed, not for diagnosis of SAH itself 2
- Neurology consult (Option C) delays definitive diagnosis; LP can be performed in the emergency department 1
- Discharge (Option D) is dangerous and violates standard of care given the classic presentation and CT limitations 1, 2
Clinical Pitfall to Avoid
Patient symptom improvement does not reduce SAH risk. The initial hemorrhage may be small, but early rebleeding occurs in 4-13.6% within 24 hours, with one-third occurring within 3 hours and carries very high mortality. 1 Missing this diagnosis has catastrophic consequences for both morbidity and mortality. 2
Answer: B. Lumbar puncture