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Capillary – Small blood vessels that normally connect the arteries (which bring blood flow to the brain) to the veins (which carry the blood flow away from the brain). The capillaries are very thin-walled, allowing the blood cells to transfer oxygen and nutrients to the brain tissue.

Catheter – A hollow flexible tube for insertion into a body cavity, duct, or vessel to allow the passage of fluids or distend a passageway. Used in the endovascular treatment of cerebral aneurysms.

Cavernous Malformation – (also known as cavernous angioma or cavernoma). A particular type of vascular malformation of the brain. This is a compact collection of abnormal dilated veins and capillaries that is located within the substance of the brain. Because these malformations do not contain arteries they are under low blood flow.

Cerebral Aneurysm – A weak bulging spot on the wall of the brain artery – also called a brain or intracranial aneurysm.

Circle of Willis – Circle of vessels around the base of the brain where most aneurysms are found.

Clipping – The traditional surgical method for repairing an aneurysm. The surgeon exposes the aneurysm and then places a metal clip that opens and closes like a clothespin across the base of the aneurysm, so that no more blood can enter the aneurysm.

Coiling – A newer treatment for aneurysms.  A neurosurgeon or neuroradiologist performs an angiogram and then passes a catheter all the way up into the skull to reach the aneurysm itself. The aneurysm is then filled with fine platinum wire to cause the aneurysm to clot off.

Craniotomy – The generic term for all operations in which the skull is opened including the surgical procedure for clipping an aneurysm or removing a vascular malformation.

CT – Abbreviation for CT scan or computed tomography scan. This is a special form of x-ray that is often the first test performed when an aneurysm rupture is suspected. It is painless and is the best x-ray test to look for blood that has escaped after an aneurysm bleeds.