Thunderclap Headache Brain Scans

Should everyone with thunderclap headache have an MRI brain scan? Arguments for and against are discussed in the April 2008 issue of the AHA Journal "Stroke".

I think that the "for" camp is winning the argument.

Historically, before brain imaging became widely available, an acute-severe-maximal-at-onset headache would have required, as a bare minimum a Lumbar Puncture test to rule out subarachnoid haemorrhage.

In the late 1970's and early 1980s Brain CAT scans / Brain CT scans became more widely available. A CT scan of brain will diagnose >95% of subarachnoid haemorrhages if performed within 24 hours of the onset of the initial thunderclap headache. With modern CT machines, the sensitivity is probably even higher (98-99%).

Now, with a much larger list of potential causes, it is becoming harder to avoid MRI scanning, as many of the causes will not be readily appreciated on CT brain, nor following lumbar puncture. A case in point would be spontaneous intracranial hypotension.

The Reversible Cerebral Vasoconstriction Syndromes are a case in point - subtle changes in vessel calibre can now be imaged on MR angiography. The white matter changes of reversible posterior leucoencephalopathy, or the subtle changes of Carotid Dissection are also best appreciated on MRI. Difficult to get at locations with brain CT scan includes the skull base (retroclival haematoma) or pituitary fossa (pituitary apoplexy), yet these areas are easily appreciated on MRI.

The days of a CT Brain, which if negative is followed by lumbar puncture are probably going to disappear.

AT present, I would be satisfied with CT + Lumbar Puncture only, so long as the original headache had resolved. If recurrent or persistent I would definitely pursue further investigation with MRi brain scan or MR cerebral angiography.

What would be a Reasonable Approach to Investigation?

1. Take the history - make sure you know the exact onset, where, why, how, when, time to maximum pain
2. Examination, including vital signs, check for meningism, Horners, rash
3. Order urgent CT Brain to exclude subarachnoid haemorrhage, but be mindful of cerebral venous sinus thrombosis, pituitary tumor, hydrocephalus
4. Perform lumbar puncture if CT does not give a definite diagnosis
More will be said about lumbar puncture elsewhere, but the principle, when testing for haemorrhage is to wait a minimum of 12 hours from first headache until testing for xanthochromia (bilirubin spectrophotometry
5. If CT and Lumbar Puncture fail to give a definite diagnosis and your patient is well, you could wait and see, especially if MRI is not readily available
6. If MRI is available, request MR Brain and MR Angiogram, and let your radiologist know if you are suspecting either malignant meningitis or spontaneous intracranial hypotension, as these diagnoses will require gadolinium enhanced imaging, or even MR myelography


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