Investigations - Brain

Patients who experience blackouts may be referred for investigations to determine whether or not there may be a primarily neurological cause for their symptoms. These may include the following:

Computerised Tomography (CT) Scanning of the Brain

This test may be performed if it is suspected that there is a problem within the brain that caused the blackout.

This is a test to look at the structure of the brain. It is mainly used to exclude strokes, hemorrhages, and large tumours or other masses. It is non-invasive although sometimes an intravenous injection of a contrast-agent (dye) is used to highlight abnormalities or to image the blood vessels to detect aneurysms (swellings in arteries) or other vascular abnormalities. You should alert the radiographer if you have ever had any allergic reactions to contrast agents, or if you are diabetic.

The scan will only take 10-15 minutes. No specific preparation is required.

Electroencephalogram - EEG

This test may be ordered if a seizure is the suspected cause of a blackout.

An EEG is a non-invasive test where electrodes are connected to the scalp in order to monitor brainwave activity. It looks for abnormalities in the electrical function of the brain. It is primarily to look for evidence for epileptic changes, but can sometimes show abnormalities in other brain conditions as well. If it is abnormal this information is very useful, but it can still be normal in patients with epileptic seizures, as the epileptic changes in the brainwaves are not always present.

An EEG usually takes about 30 minutes to perform by a technician and is interpreted later by a neurologist. You are normally just required to sit quietly during the recording and at the end do some deep breathing and have some lights flashed in your eyes. There is usually no special preparation required, but sometimes a sleep deprived EEG is performed so that you will need to stay up the night before. You will be instructed if this is necessary.

Sometimes more prolonged EEG monitoring is performed during the day for several hours and occasionally patients are admitted to hospital for several days of EEG monitoring. This type of monitoring is to try and catch suspected seizure episodes and for this reason video monitoring to visualise the episodes is also performed.

Magnetic Resonance Imaging (MRI) of the Brain

This test may be ordered to investigate blackouts if a problem within the brain is the suspected cause of a blackout and either the CT and EEG are normal or to further investigate abnormalities found on CT and EEG.

An MRI is a scan which examines the structure of the brain in more detail than a CT scan. It can pick up more subtle abnormalities than a CT scan, particulary small areas of scarring (sclerosis) which can be associated with seizure activity. It can also detect evidence of other neurological diseases like multiple sclerosis and can also image the arteries and veins of the brain without giving an injection of a contrast agent. Unlike a CT scan no X-rays are used and so there is no radiation exposure. Most MRI scans involve putting the patient into a very small tunnel, and patients who are very claustrophic (scared of enclosed spaces) may require sedation. The MRI scanner also uses a very powerful magnetic field and so patients with certain metal devices (especially pacemakers, aneurysm clips, bionic ears, endoscopy capsules) or who have had metal fragments in their eyes or near other delicate tissues will not be able to have one.

Usually an MRI is non-invasive but occasionally an injection of a contrast agent will be required to further define some abnormalities.

The scan will normally take about 20 minutes and no special preparation will usually be required.

Carotid Doppler Ultrasound

This test is rarely ordered in the investigation of blackouts. It may be ordered if there was weakness of one side of the body or abnormal speech when the person awoke from the blackout. It can be helpful to give initial information about the blood vessels at the back of the brain.

Carotid Doppler Ultrasound is a scan which uses ultrasound and doppler soundwaves to image the carotid arteries in the neck. These are the arteries at the front of the neck which carry most of the blood to the brain. Narrowings or blockages of these arteries can affect blood flow to the brain and cause strokes. The smaller vertabral arteries at the back of the neck can also be imaged, but not in as much detail.

Narrowings of the vertebral arteries can be associated with blackouts. Narrowings or bloackages of the carotid arteries rarely cause blackouts.

This test is completely non-invasive and no special preparation is required. It will take about 15-20 minutes.

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