See, Aneurysm means abnormal out pouching of a cavity or blood vessel due to thinning of the wall. This may occur inside the heart (a condition called Ventricular Aneurysm). But, this usually occrs following a major heart attack. Considering, your cousins history (and I think he is a young person), he most probably has an aneurysm of the major vessel, Aorta. This again is due to a weakened vascular wall and may occur within the chest (Thoracic Aorta) or abdomen (Abdominal Aorta). This weakening is usually due to a congenital condition, and if your cousin has tall, thin body habitus with large flexible fingers he may have a condition called Marfan s Sndrome. This condition is very well diagnosed by Contrast CT Scan and needs surgical repair, if sufficiently large. Sometimes, congenital vascular aneurysms may occur inside brain. They may also occur in limb vessels after a trauma.