The first test ordered by the doctor is an MRI (magnetic resonance image) of the brain. This is the best form of brain imaging available today and demonstrates the tumour in the majority of cases, as well as often giving a clue as to the tumour type.
If there is a high chance that the tumour is actually a secondary tumour that has spread from a cancer that started outside the central nervous system, the doctor will search for possible primary cancer in the lungs (chest x-ray), breasts (palpation and mammography) etc. before recommending surgical attack or biopsy of the brain tumour itself. Even so, sometimes the answer on pathological exam of the surgical specimen still demonstrates that the tumour started outside the brain – ‘occult primary’.
The certain diagnosis of a brain tumour is established for sure by surgical biopsy.
Sometimes, the biopsy material is obtained and the initial treatment given all at the same operation, when the surgeon operates to remove as much tumour as possible and also sends this resected material to the laboratory for microscopic analysis. It is the microscopic of material from the tumour that gives the certain diagnosis as to exactly what kind of tumour it is.
In pituitary tumours that over-secrete hormone products and intracranial germ cell tumours that over-secrete HCG and/or AFP (see testicular cancer section for explanation of these terms) then the diagnosis may be established from serum testing together with the MR image of a brain tumour that fits the picture.