Diagnosis

How a brain tumour diagnosis is made

The bones of the skull hide brain tumours. You cannot feel or see them during a routine examination. Scans produce pictures that suggest a particular type of tumour. And fortunately we have lots of weaponry to diagnose brain tumours without invading the body. But the only reliable way to an accurate diagnosis is to examine a sample of a tumour under a microscope, so a biopsy will sometimes need to be done. If this type of examination is not possible, an educated assumption is made based on available test results.

If there is a suspicion that there might be a brain tumour, then your doctor has a whole host of diagnostic weaponry, which will aid an accurate diagnosis. These tests determine firstly whether you have a brain tumour and then, if you do, what type of tumour.

 

MRI scan – magnetic resonance imaging. This uses magnetic and radio waves, so no exposure to X-rays or any damaging forms of radiation. An MRI scan takes pictures from any direction. Contrast agents (usually gadolinium) can be used to delineate the lesion. These are usually injected into the arm during the scan. This has made some of our patients feel sick but this could be the thought of the injection. Needles are scary things.

Just a word about pacemakers; you may not be able to have an MRI scan if you have a pacemaker fitted or other metal objects in your body but alternatives are offered. Some new pacemakers are MRI compatable though – you will need to check with your cardiologist.

The scan will last about 45 minutes and can be noisy. Some hospitals let you listen to a CD so take one just in case.

Other tips if you need an MRI scan – wear warm clothing; it can be chilly in the room. You will need to take off jewellery and anything else metal. This includes underwired bras and jeans with studs in.

If you have a child undergoing an MRI scan, get them to imagine they are going into a space capsule.

You should receive the results within two weeks. Privately, you can have the scan and reporting done on the same day, but private scans can be expensive. You can get one done privately with a report for a little over £200 – it depends where you go.

 

CT scan – computerised tomography. Instead of sending out a single x-ray through the body, several beams are sent simultaneously from different angles. The computer then processes the results showing them as a 2D picture. CT scans are less expensive and take less time than an MRI scan, but they have lower resolution so could potentially not show some skull base and low grade tumours, as well as an MRI scan. So, if you have one type of scan rather than another, it is usually because one will be more suited to you.

A CT scan usually lasts around 20 minutes and is quieter than an MRI scan. You lie on a table and the scanner moves around your head. If you need a contrast scan, then an iodine-based contrast agent will be injected. This shows the ‘leaky’ blood vessels in a tumour and enables the neuro-radiologist to see the mass directly.

Other tips if you are having a CT scan - Warm clothing is recommended; it can be chilly in the room. And if you are allergic to shellfish let the radiographer know, because some contrast agents contain iodine.

Reporting is usually done within two weeks. Again – this may be sooner if you have a private CT scan.

 

PET scan – position emission tomography. Only a few hospitals in the UK have a PET scanner. This too produces a 3D image but in colour. The patient is given radiation via a medicine called a radiotracer. This goes to the part of the body that needs to be examined. The PET scan then detects radiation inside the body and makes images that show how the radiation is being broken down. This type of scan is not generally used to diagnose a brain tumour, but it can provide additional information about the nature of the tumour. For example, it may help to determine the difference between a benign and malignant tumour because malignant tumours are more metabolically active (that means that within the tumour cells that are alive and growing, chemical reactions are happening within them). And it can show the effects of treatment. For more information about the difference between benign and malignant tumours visit anatomy and tumour types.

The scan itself takes about 30 minutes. About 40 minutes before the scan the patient is injected with a mildly radioactive substance which has no risk to the body as the level of radiation is very small.

 

SPECT – single photon emission computed tomography. Similar to PET, a SPECT scan views how blood flows through arteries and veins in the brain. It differs though from a PET scan in that the chemical stays in your blood stream rather than being absorbed by surrounding tissues, thereby limiting the images to areas where blood flows. SPECT scans are cheaper and more readily available than higher resolution PET scans.

As with the PET scan, an injection of a small amount of radioactive tracer is given prior to the scan. Then you'll be asked to rest for about 10-20 minutes until the tracer reaches your brain. Next you'll lie comfortably on a scanner table while a special camera rotates around your head. You have to remain as still as possible so that the machine can get accurate pictures.

Other tip: be sure to drink plenty of fluids to flush out any tracer left in your body.

 

Angiography - this shows the blood vessels in the brain – the arteries, the veins and sinuses. Angiography will not feel any different to having a CT or MRI scan if it is done as a CT or MRI angiogram.

It can also be done with an injection of iodine dye into the femoral artery in the groin, which is then threaded through to the brain. This sounds worse than it is; a numbing agent is used and you may feel brief pain when the catheter is inserted. Sedation is sometimes given for this test.

You will feel a hot, flushed sensation lasting from 5 to 20 seconds as the images are taken. This may be repeated several times in order to view all necessary arteries, so this test can last several hours. You will need to be careful afterwards to prevent bleeding. In some instances, a puncture closure may be used which will allow you to get up and move around sooner.

Any invasive test carries risk. There is a very small risk of the catheter damaging your artery or loosening a piece of plaque lining the artery wall. And then there is the risk of sensitivity to the contrast agent used. The most common side effects from the iodine contrast are a brief metallic taste in your mouth and a feeling of warmth throughout your body.

 

Information courtesy of brainstrust