Investigation | Indications | Causes that may be detected by this investigation |
Non-contrast CT brain scan (with visualisation of sinuses if symptoms suggest acute sinusitis) | All thunderclap headaches as first investigation | Subarachnoid haemorrhage (90% within the first 24 h), intracerebral haematoma, intraventricular haemorrhage, subdural haematoma (rare cause of thunderclap headache), some infarcts particularly in the cerebellum, hydrocephalus, tumours, acute sinusitis |
CSF | All CT normal thunderclap headaches | Subarachnoid haemorrhage, meningitis |
ESR and C reactive protein | Age >60 years | Giant cell arteritis (very rare cause of thunderclap headache) |
MRI (diffusion, FLAIR, gradient-echo, sagittal T1, T1 with gadolinium, cervical FAT/SAT), MRA and MRV | All thunderclap headaches after normal CT and normal or near normal CSF. | Intracranial venous thrombosis, dissection of cervical arteries (extra or intracranial, carotid or vertebral), pituitary apoplexy, reversible cerebral vasoconstriction syndrome, unruptured but symptomatic aneurysm (eg, third cranial nerve palsy). |
Fewer sequences if cervical and transcranial Doppler shows abnormalities suggesting dissection or an increase in intracranial flow velocities suggesting reversible cerebral vasoconstriction syndrome | Acute infarct less than 3 h not visualised on CT scan, CSF hypotension, and better visualisation of all abnormalities previously seen on CT. | |
Catheter angiography | Gold standard for subarachnoid haemorrhage. Particularly if increasing headaches, and occurrence/increase of focal deficits, unexplained after CT scan, CSF analysis and complete MRI/MRA/MRV | Ruptured aneurysm in 85% of patients with subarachnoid haemorrhage, intracranial venous thrombosis, dissection (cervical, intracranial), reversible cerebral vasoconstriction syndrome, differential diagnosis of cerebral arteritis, unruptured but symptomatic aneurysm (third nerve palsy) |
ESR, erythrocyte sedimentation rate; MRA, MR angiography; MRV, MR venography.