Stroke causes. Artwork showing the three causes of a stroke, a loss of brain function(s) due to an interruption in blood supply. The interruption in blood supply may be due to a thrombus (blood clot, top), embolism (air bubble or loose blood clot, centre), or an aneurysm (weakened blood vessel wall, bottom), which may or may not rupture. The upper two diagram are examples of ischaemic strokes, while a ruptured aneurysm is an haemorrhagic stroke.