abnormal ascending aorta morphology thoracic aorta aneurysm ascending aorta aneurysm 2010-10-19T10:56:31Z MPheno.ontology MP:0010661 csmith Fyler:2310 a protruding sac formed by the dilation of the wall of the of the part of the aorta that arises from the base of the left ventricle and extends upward to the aortic arch, resulting from a weakening of the vessel wall