MRI Scan for Brain Tumours: What to Know

Around 12,000 people are diagnosed with a brain tumour in the UK each year, and roughly 5,300 of those are malignant (high-grade). MRI is the gold standard investigation for detecting, characterising, and monitoring brain tumours. It can identify tumours as small as a few millimetres, show their relationship to surrounding brain structures, and help distinguish between different tumour types — all without radiation or surgery.

If you are experiencing symptoms that might suggest a brain tumour — persistent headaches, seizures, neurological changes, or personality shifts — an MRI is the most important diagnostic step.

Types of Brain Tumours

Brain tumours are classified as primary (originating in the brain) or secondary/metastatic (cancer that has spread from elsewhere in the body). Secondary brain tumours are actually more common than primary ones in adults.

Common Primary Brain Tumours

• Gliomas — arise from glial cells (supporting cells of the brain). Include astrocytomas, oligodendrogliomas, and ependymomas. Graded from I to IV by the WHO classification. Grade IV (glioblastoma) is the most common malignant primary brain tumour in adults, with around 2,200 new cases per year in the UK.
• Meningiomas — arise from the meninges (brain coverings). The most common primary brain tumour overall. Usually benign (WHO grade I). More common in women. Many are found incidentally and never need treatment.
• Pituitary adenomas — benign tumours of the pituitary gland. Found incidentally in up to 10% of brain MRIs. Most are small (microadenomas, under 10mm) and clinically insignificant.
• Acoustic neuromas (vestibular schwannomas) — benign tumours on the hearing/balance nerve. Cause one-sided hearing loss, tinnitus, and balance problems. Around 1,200 diagnosed per year in the UK.
• Medulloblastomas — the most common malignant brain tumour in children. Arise in the cerebellum (back of the brain).

Secondary (Metastatic) Brain Tumours

The most common cancers to spread to the brain are lung, breast, melanoma, kidney, and bowel. Around 35,000 people develop brain metastases in the UK each year — far more than primary brain tumours.

Symptoms That May Indicate a Brain Tumour

Symptoms depend on the tumour's location, size, and growth rate:

• Headaches — typically worse in the morning, with coughing, straining, or bending forward. May wake you from sleep. A new headache pattern, not just a worsening of existing headaches.
• Seizures — a first seizure in an adult is investigated with MRI. Around 30-50% of brain tumour patients present with seizures.
• Neurological deficits — weakness, numbness, speech difficulty, visual disturbance, coordination problems — depending on which part of the brain is affected.
• Personality or cognitive changes — especially with frontal lobe tumours.
• Nausea and vomiting — particularly if worse in the morning, suggesting raised intracranial pressure.
• Visual changes — blurred or double vision, visual field loss.
• Hearing loss or tinnitus — particularly one-sided (acoustic neuroma).

These symptoms can all have benign causes, which is far more likely. But they warrant investigation to rule out a tumour.

What Brain MRI Shows for Tumour Detection

A brain MRI with contrast (gadolinium) is the standard protocol for tumour assessment. The radiologist looks at:

• Mass lesion — size (measured in three dimensions), location, margins (well-defined or irregular).
• Signal characteristics — different tumour types have characteristic appearances on T1, T2, and FLAIR sequences. Glioblastomas typically show irregular ring enhancement with central necrosis. Meningiomas show homogeneous enhancement with a "dural tail."
• Contrast enhancement pattern — most malignant tumours enhance (light up) after gadolinium injection because of their leaky blood-brain barrier. Some benign tumours also enhance (meningiomas, acoustic neuromas).
• Surrounding oedema — vasogenic oedema (swelling) around a tumour appears bright on T2/FLAIR. The extent of oedema does not necessarily indicate malignancy — meningiomas can cause significant surrounding oedema.
• Mass effect — shift of midline structures, compression of ventricles, or herniation. Indicates the tumour is exerting pressure on the brain.
• Hydrocephalus — enlargement of the ventricles if the tumour is blocking normal CSF flow.
• Multiplicity — multiple lesions suggest metastatic disease rather than a primary tumour (though some primaries can be multifocal).

Advanced MRI Techniques for Brain Tumours

• MR spectroscopy — measures chemical metabolites within the tumour. Increased choline and reduced NAA suggest high-grade malignancy. Can help distinguish tumour from infection or inflammation.
• MR perfusion — measures blood flow within the tumour. High blood volume suggests high-grade tumour. Used for grading and monitoring treatment response.
• Diffusion-weighted imaging (DWI) — restricted diffusion in a brain lesion suggests high cellularity (more aggressive tumour) or abscess (infection).
• Functional MRI (fMRI) — maps brain activity to locate speech, motor, and visual centres relative to the tumour. Used for surgical planning to avoid critical brain areas.
• Diffusion tensor imaging (DTI/tractography) — maps white matter tracts (nerve fibre bundles) running near the tumour. Another surgical planning tool.

What to Expect During the Scan

A brain MRI for tumour assessment takes 30-45 minutes (longer than a standard brain MRI because contrast and additional sequences are included). You lie on your back with your head in a head coil. A cannula is placed in your arm for the contrast injection.

The contrast is injected part-way through the scan. You may feel a brief cool sensation in your arm. Serious reactions to gadolinium are very rare (around 1 in 40,000). The rest of the scan continues after injection to capture the enhancement pattern.

Preparation

You may need a recent kidney function blood test (eGFR) before the contrast injection, particularly if you are over 60 or have kidney problems. Eat, drink, and take medications normally. Remove jewellery and hair clips.

What Brain MRI Cannot Do

• Confirm the tumour type — MRI can suggest a likely diagnosis based on appearance, location, and enhancement pattern, but definitive diagnosis requires tissue (biopsy or surgical removal). Molecular and genetic analysis of tumour tissue is now essential for grading and treatment planning.
• Detect very small tumours — MRI has a resolution limit of approximately 1-2mm. Very early-stage or microscopic tumour deposits may not be visible.
• Assess the whole body for spread — brain MRI only covers the head. If metastatic disease is suspected, additional imaging (CT chest/abdomen/pelvis, PET-CT) is needed.

Treatment Pathways

• Observation — for small, asymptomatic, likely benign tumours (small meningiomas, pituitary microadenomas). Repeat MRI at intervals (typically 6-12 months initially, then annually).
• Surgery — the primary treatment for most accessible brain tumours. Aims for maximal safe resection while preserving neurological function. Awake craniotomy (where you are conscious during surgery to protect speech and motor areas) is used for tumours near critical brain regions.
• Radiotherapy — used alone or after surgery. Stereotactic radiosurgery (Gamma Knife, CyberKnife) delivers a highly focused radiation dose to small tumours and is effective for acoustic neuromas, small meningiomas, and single brain metastases.
• Chemotherapy — temozolomide is the standard chemotherapy for glioblastoma and high-grade gliomas. Given alongside and after radiotherapy.
• Targeted therapy and immunotherapy — emerging treatments based on the molecular profile of the tumour. Becoming standard for certain tumour subtypes.
• Multidisciplinary team (MDT) — all brain tumour patients are discussed at an MDT meeting involving neurosurgeons, neuro-oncologists, neuroradiologists, neuropathologists, and clinical nurse specialists.

UK Statistics

• Around 12,000 people are diagnosed with a brain tumour in the UK each year
• 5,300 are malignant (high-grade)
• Glioblastoma (grade IV) accounts for around 50% of malignant primary brain tumours in adults
• Meningiomas account for about 36% of all primary brain tumours
• Brain tumours are the leading cause of cancer death in children and young adults under 40
• Around 35,000 people develop secondary (metastatic) brain tumours annually
• 5-year survival for all brain tumour types combined: approximately 40% for malignant, 90%+ for benign

Frequently Asked Questions

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