Aneurysm: Abnormal swelling of an artery. Eventually over a number of years this may tear and burst; causing a sudden escape of blood.

Angiogram: X-ray examination of the blood vessels. It is a common test for neurological conditions.

Arachnoid: The middle membrane layer of the three which cover the brain and spinal cord.

Artery: A vessel carrying blood away from the heart. The blood in the arteries is under high pressure and so the walls of the arteries are thick.

Capillaries: Network of fine blood vessels that carry blood between the smallest arteries and veins.

Craniotomy: An opening made by a neurosurgeon to gain access to the brain.

CT scan: X-ray that provides cross section pictures of the body.

Cerebro-spinal Fluid: Clear watery fluid that protects and surrounds the brain and spinal cord.

Congenital: A condition which is present from birth.

Contrast dye: A substance which is injected in to the body to show up the difference between tissue types.

Dural: Relating to the Dural Mater - the outermost membrane around the brain and spinal cord.    

Epilepsy: Disorder of the brain function. There are many types of seizure.

Haemorrhage: The escape of blood from a ruptured blood vessel - when a sudden bleed occurs around the brain it causes a stroke.

Hereditary Haemorrhagic Telangiectasia: This is a rare inherited condition that runs in families; also known as Osler-Weber-Rendu disease. It causes nose bleeds, red spots on your skin and occasionally bleeding from other parts of the body.

Lethargy: A state of physical slowness and mental dullness.

Lumbar Puncture: A medical procedure that extracts cerebro-fluid to aid diagnosis. This procedure is achieved by inserting a needle into the sub-arachnoid region of the lower back.

MRI Scan: Scan that uses magnetic fields and radio waves to provide images.

Neurological: A term for conditions that occur in the nervous system.

Neuroradiologist: A doctor specially trained to conduct and interpret CT, MRI scans and angiograms. They also treat vessels using embolisation techniques.

Neurosurgeon: A doctor who diagnoses and treats people with disorders of the brain and spine using surgical techniques.

Nidus: The tangle of blood vessels within an AVM.

Shunt: A direct flow of blood from an artery to a vein.

Stroke: A sudden episode of weakness that affects one side of the body and is caused by an interruption to the flow of blood to the brain.

Sub-arachnoid haemorrhage: Is a sudden leak of blood over the surface of the brain. The brain is covered by a number of membranes; one of them is called arachnoid. A haemorrhage that occurs beneath this layer is a sub-arachnoid haemorrhage.

Vascular: Relating to blood vessels.

Veins: Return blood back to the heart from the tissues, bringing back the waste products - carbon dioxide, water and waste metabolites. Blood in the veins is under low pressure and the walls are thin.