Thunderclap Headache With a Normal CT
Ms. R is a 41-year-old woman who presents to the emergency department 4 hours after the sudden onset of a “thunderclap” headache during a vigorous workout. The pain reached 10/10 within seconds and is still severe. She has nausea, photophobia, and mild neck stiffness. She has no fever, no focal weakness, and no prior headache history, although she has had migraines in the past and says this is different. Blood pressure is 168/98 mmHg, heart rate 92/min, and temperature 37.1°C. Neurologic examination, including fundoscopy, is normal. A noncontrast CT of the head performed 5 hours after symptom onset is reported as normal by the radiologist. The emergency physician asks whether she can be discharged with analgesia and outpatient follow-up. She is alone and has no reliable ride home.
1. What is the next step in investigation, and why is a normal CT insufficient here?
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She should not be discharged. The priority is to exclude subarachnoid hemorrhage (SAH). A noncontrast CT is most sensitive very early after symptom onset, but sensitivity is not 100%, especially as time passes and with smaller bleeds. A normal CT at 5 hours is reassuring but does not fully exclude SAH in a patient with a classic thunderclap headache, neck stiffness, and photophobia.
The next step is a lumbar puncture (LP), ideally at least 12 hours after symptom onset, to allow xanthochromia to develop. If LP is performed too early, it may be falsely negative. If the CT were negative and LP cannot be done safely or is delayed, CT angiography could be considered, but it does not replace LP for excluding SAH in all cases. Before LP, review contraindications: coagulopathy, anticoagulation, platelet count, intracranial mass, and local infection. Obtain consent and explain that a positive LP would lead to urgent neurosurgical/neurointerventional involvement. She also needs analgesia, blood pressure reassessment, and observation; discharge with a presumed migraine is unsafe.
2. The LP shows 2,000 red cells/µL in tube 1 and 1,900 in tube 4, and xanthochromia is present. What is the diagnosis and immediate management?
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This is subarachnoid hemorrhage until proven otherwise, likely aneurysmal. The red cell count does not fall significantly between tubes, and xanthochromia indicates bilirubin from red cell breakdown in cerebrospinal fluid, which is not explained by a traumatic tap alone. Immediate management includes admission to a monitored setting, urgent CT angiography or catheter angiography, and neurosurgical/neurointerventional consultation.
Start nimodipine 60 mg orally or by nasogastric tube every 4 hours to reduce delayed cerebral ischemia, unless contraindicated by hypotension. Maintain normovolemia and avoid both hypotension and hypertension; treat pain and nausea. Monitor for hydrocephalus, seizures, hyponatremia, and rebleeding. Do not give anticoagulants or antiplatelets. Transfer to a centre with neurointerventional and neurosurgical capability. Discuss with the patient and family that the goal is early aneurysm securing, because rebleeding carries high mortality. Document the time of onset and all neurologic changes.
3. If the LP had been negative, how would you counsel and follow up?
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A completely negative CT and appropriately timed LP make SAH very unlikely, but the evaluation is not purely binary. She should be reassessed clinically and counselled about return precautions: sudden severe headache, fever, neck stiffness, weakness, confusion, seizure, or persistent vomiting requires immediate return. Consider other causes of thunderclap headache, including reversible cerebral vasoconstriction syndrome, cerebral venous sinus thrombosis, arterial dissection, and pituitary apoplexy, especially if the headache recurs or examination changes.
Arrange follow-up within 1–2 weeks with a primary care clinician or neurologist. Advise avoiding triggers such as strenuous exertion and sympathomimetics until reviewed. If the headache recurs in a stereotyped thunderclap pattern, further vascular imaging may be needed. Do not label it definitively as “just a migraine” without follow-up. Provide analgesia, antiemetics, and a clear safety net. Because she lives alone, confirm how she will get home and who can check on her. Document that SAH was discussed and that return precautions were understood.