Post-coil headache in a patient with a coiled aneurysm: imaging triage under time pressure

Next step: urgent lumbar puncture (LP) if CT is negative, and MRI/MRA of the brain including susceptibility-weighted imaging (SWI) and time-of-flight (TOF) MRA as the cross-sectional test of choice - not CTA.

Reasoning:

1. CT sensitivity for subarachnoid haemorrhage (SAH) falls with time. A modern non-contrast CT is ~95–100% sensitive for SAH within 6 hours of onset in experienced hands, but sensitivity drops to ~85–90% by 12–24 hours and lower thereafter. A 'normal' CT at 4 hours is reassuring but does not exclude SAH, particularly in a patient with a prior aneurysm and a sudden maximal-onset headache (thunderclap).
2. LP is the established next step when CT is negative and clinical suspicion remains; xanthochromia (bilirubin) is more specific than oxyhaemoglobin and should be assessed if the local laboratory supports spectrophotometry. LP should be performed after at least 12 hours from onset where possible to allow bilirubin formation, but should not be delayed indefinitely if the clinical picture is compelling.
3. CTA is not the right tool here. CTA is used to detect the causative aneurysm, not to diagnose SAH. In a patient with a known coiled ACom aneurysm, beam-hardening and coil mass artefact degrade the ACom region on CTA, and a 'negative' CTA would not exclude re-bleeding at the coil neck. CTA also does not assess the subarachnoid spaces for blood.
4. MRI/MRA is superior for this specific question. SWI is exquisitely sensitive to haemosiderin and can detect small amounts of subarachnoid or cortical blood, including blood obscured by coil artefact on CT. TOF MRA (or contrast-enhanced MRA if TOF is degraded by coil artefact) assesses the coil mass, neck remnant, and parent vessels without ionising radiation. In a patient with eGFR 55, gadolinium-based contrast is acceptable at standard doses with no evidence of NSF risk at this eGFR, but TOF avoids contrast entirely.
5. Safety and communication. The patient should not be discharged 'to come back if worse' - thunderclap headache with a prior aneurysm warrants admission, observation, and a definitive diagnostic pathway. Document the reasoning in the notes and discuss directly with the emergency physician, explaining that the request for CTA addresses a different question (aneurysm morphology) than the immediate clinical question (has there been re-bleeding?).

Interpretation: this pattern is consistent with SAH, but a traumatic tap must be actively excluded.

Reasoning:

1. Uniform blood staining across tubes suggests blood was present in the subarachnoid space before the needle entered, rather than blood introduced by the needle. However, a traumatic tap can also produce blood in all tubes if bleeding is brisk, so the finding is supportive, not definitive.
2. Xanthochromia is the discriminator. Centrifuge the sample promptly and assess supernatant for bilirubin (yellow) by spectrophotometry. Bilirubin indicates in vivo haemoglobin breakdown and is highly specific for true SAH when assessed ≥12 hours after onset. Oxyhaemoglobin alone can occur in traumatic taps and is less specific.
3. If xanthochromia is present or the clinical picture is compelling, the patient has SAH until proven otherwise. This changes management to: neurosurgical/neurointerventional review, blood pressure control, nimodipine, and definitive vascular imaging to identify the source.
4. Definitive vascular imaging in this setting is catheter digital subtraction angiography (DSA), which remains the reference standard for detecting a recurrent or residual aneurysm at a coiled ACom segment, particularly when coil artefact limits non-invasive assessment. CTA and MRA can be complementary but are less sensitive for small neck remnants.
5. If xanthochromia is absent and the tap is traumatic, the patient still requires close observation and repeat clinical assessment; a single negative LP does not entirely exclude a small sentinel bleed, and the prior aneurysm history lowers the threshold for further imaging (MRI with SWI, and consideration of DSA if suspicion persists).
6. Documentation and communication with the patient and the treating team are essential, including explaining that the LP result must be interpreted alongside the timing of onset and the imaging findings.

Counselling:

1. Explain in plain language that a normal CT scan does not completely exclude bleeding around the brain, especially when performed several hours after the headache started, and that a lumbar puncture and/or MRI are needed to be confident.
2. Explain that she has a known treated aneurysm, which raises the stakes: if there has been a small re-bleed or a change at the coil site, early detection allows early treatment and reduces the risk of a larger, more dangerous bleed.
3. Explain that discharge with 'return if worse' advice is not safe in this context because a second, larger haemorrhage can occur suddenly and with high morbidity and mortality; the purpose of admission is to complete the diagnostic pathway and observe her.
4. Acknowledge her anxiety and explain the timeline: LP, MRI/MRA, and review by the neurosciences team, with a clear plan for what happens if tests are negative.

Medico-legal considerations:

1. Document the reasoning for not discharging, including the limitations of the early CT, the plan for LP and MRI, and the discussion with the patient and the emergency physician.
2. Document the discussion with the patient about risks, benefits, and alternatives, and her agreement to be admitted.
3. Escalate appropriately if there is pressure to discharge; a senior clinician (neurology/neurosurgery) should be involved and the decision recorded.
4. Avoid a false sense of security from a single 'normal' report; record that the CT was performed at 4 hours and that this does not exclude SAH.
5. Follow local policy on incidental findings and communication of results; ensure the patient knows who to contact and when.
6. Recognise the limits of the resident's report - a normal CT read by a junior does not close the case; a senior review and a structured diagnostic pathway are required.