There are two common sorts of brain scan.
CT stands for Computed Tomography. This works by x-rays.
MRI stands for magnetic resonance imaging. This works by magnetism and radio waves.
Both types of scan use complex computer programmes to build up a cross-sectional picture of the body or brain
The scan shows the physical structure of the brain. It does not show how the brain works. To use a computing analogy, the scan checks the hardware of the brain, not the software.
Almost all headaches are what is known as primary headache. Using the computing analogy again, this is a software problem so does not show up when the hardware is checked.
Pain is important, to warn of injury or disease: it is an alarm signal. The longer you have headache, the less chance of the cause showing up on a scan. However like a faulty fire alarm, or the oil light in your car-it often happens when there is an electrical fault in the system. The longer the warning goes on with nothing else bad happening, the less likely there is a serious underlying cause.
If there are other symptoms such as epileptic attacks, paralysis, or a clinic change in brain function, then those symptoms independently may warrant a brain scan.
There are three main situations where headache alone requires a brain scan:
Migraine is a common disease, affecting one in ten people. Therefore it follows that one in ten people who are diagnosed with a brain tumour, have a history of migraine.
Headache is so common, that it is neither practicable nor cost-effective to scan everybody. If everyone has a scan, how often should the scan be repeated if headache continues? It becomes impossible. If everyone with headache simply joined a queue for a scan, some people with bleeding in or around the brain would die while waiting only a few days for their scan and some with tumours would die within a few weeks. It follows that, even if we can afford to scan everyone, doctors must use clinical skill to prioritise the scans.
CT scans use x-rays which can cause cancer. Children who have has a CT scan have a 20% increased risk of cancer, it is likely adults have a similar risk. Some significant abnormalities found on MRI scans cannot be seen on CT, so there is a small chance of false reassurance from a normal CT scan.
MRI scanning takes longer than CT and normally requires the patient to lie still in a noisy high-tech tube, which is not very pleasant, however it does avoid the risk of radiation.
The main problem with MRI scans is ‘looking for a shilling and finding a sixpence,’ in finding abnormalities that are unrelated to headache, entirely by chance. The risk of a minor abnormality of no medical significance is 1 in 4. The risk of a chance abnormality that might need treatment is about 1 in 40. Once these ‘incidentalomas’ have been found, the patient may then find it difficult to obtain insurance (for example travel) and there is often a temptation to repeat the scan time and time again to check that the ‘incidentaloma’ is not changing.
In the private sector, an MRI scan costs around £400. On the NHS the cost is probably around £200. So theoretically the NHS would be spending a billion pounds if the attempted to scan everyone with headache in the UK.
This information is provided as a general guide only and is not a comprehensive overview of prescribing information. If you have any queries or concerns about your headaches or medications please discuss them with your GP or the doctor you see at the National Migraine Centre.