How brain tumours are diagnosed

The first test in almost every suspected brain tumour is an MRI with contrast. It shows the location, size, shape and vascularity of the lesion, and gives strong clues about what type of tumour it is.

Additional imaging is often useful: MR spectroscopy looks at the chemical fingerprint inside the lesion, MR perfusion assesses blood flow, and functional MRI maps important brain areas nearby. In some cases we do a PET scan to look for tumour activity elsewhere.

Blood tests, a hearing test (for tumours near the ear), a visual field test (for tumours near the optic pathways) and endocrine bloods (for pituitary tumours) are common add-ons.

The definitive answer, however, almost always requires tissue. Either an image-guided needle biopsy or, more commonly, tissue taken at the time of surgical removal is sent to pathology. The final diagnosis — tumour type, grade, and increasingly its molecular signature — drives every treatment decision that follows.