dissecting aneurysm [L, dissecare, to cut apart; Gk, aneurysma, a widening] , a localized dilation of an artery, most commonly the aorta, characterized by a longitudinal separation of the outer and middle layers of the vascular wall. Aortic dissecting aneurysms occur most frequently in men between 40 and 60 years of age and are preceded by hypertension in more than 90% of cases. Blood entering a tear in the intimal lining of the vessel causes a separation of weakened elastic and fibromuscular elements in the medial layer and leads to the formation of cystic spaces filled with matrix. Dissecting aneurysms in the thoracic aorta may extend into blood vessels of the neck. Rupture of a dissecting aneurysm may be fatal in less than 1 hour. Treatment consists of resection and replacement of the excised section of aorta with a synthetic prosthesis. See also aortic aneurysm.
