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Balloon angioplasty – In the setting of severe vasospasm, the neuroradiologist may perform an angiogram and then pass a catheter with a balloon on its tip all the way up into the narrowed brain artery, then inflate the balloon to mechanically dilate the artery.

Balloon test occlusion – A procedure performed by a neuroradiologist or neurosurgeon in which an artery is temporarily blocked while the patient is awake in order to determine whether it is safe to permanently block the artery. In rare cases when neither clipping nor coiling is possible, aneurysms are treated by blocking the entire involved artery and aneurysm together (see parent artery occlusion).

Brain Aneurysm – A weak bulging spot on the wall of the one of the arteries in the brain, also called an intracranial or cerebral aneurysm, or berry aneurysm.

Bypass – A surgical operation in which the surgeon creates a new channel to bring blood flow to the brain. In rare cases when an aneurysm can’t be clipped or coiled, the surgeon may have to perform a bypass operation, bringing blood flow through a new channel beyond the aneurysm and then trapping the segment of the artery with the aneurysm between clips.