The statistics are on your side
Almost everyone gets a headache at some point, and the vast majority are migraine or tension-type. Brain tumours, aneurysms and haemorrhages are, in terms of frequency, rare causes of headache. Starting there keeps this piece from being read with more fear than it deserves.
That said, there are specific patterns that should send a headache for imaging. It is not intensity or duration on their own: it is how it starts, what accompanies it, and who it happens to.
Thunderclap headache: an immediate emergency
A headache reaching maximum intensity within seconds, described as the worst of a lifetime, is what is called a thunderclap headache, and it means going to an emergency department immediately. The first cause to exclude is subarachnoid haemorrhage from a ruptured aneurysm.
It is usually accompanied by vomiting, neck stiffness, light intolerance and sometimes transient loss of consciousness. It is not an intense migraine: it is a different category. Plain head CT in the first hours is highly sensitive, and if negative while suspicion persists, it is completed with lumbar puncture.
The other patterns that demand investigation
A headache that is new and different from your usual one, especially after fifty. Pain that worsens progressively over weeks. Pain that wakes you at night or is worse on waking. Pain that increases on coughing, sneezing, bending or straining. Headache with fever and neck stiffness.
And above all, headache with any neurological sign: seizure, double vision, visual field loss, one-sided weakness or numbness, difficulty speaking, clumsiness, or changes in behaviour or memory noticed by the family. That combination most justifies an MRI.
Situations that lower the threshold
Some contexts warrant earlier investigation: a history of cancer, immunosuppression or HIV, anticoagulant use, pregnancy and the postpartum period, and recent head trauma even if it seemed minor. In those cases a new headache deserves more attention than it would in someone else.
Posture also changes the approach: pain that clearly appears or worsens on standing and eases on lying down suggests cerebrospinal fluid hypotension, while pain worse on lying down may suggest raised intracranial pressure. These are clues that direct the work-up.
What frequent headaches do not mean
Having migraine, even disabling and frequent migraine, does not raise your chance of having a brain tumour. And repeating MRI scans for an already diagnosed migraine with an unchanged pattern adds nothing, while generating incidental findings that worry people unnecessarily.
What matters is not frequency but change. If your usual headache changed in character, intensity or timing, or started coming with something new, that is a reason to be seen.
Bring your imaging and settle the question
One consultation with your MRI or CT in hand is worth more than ten internet searches. Book by phone or through the form and you will be told what is there, what it means and what your options are.