- Syphilitic Aneurysms arise during tertiary syphilis due to chronic inflammation in the tunica adventitia of large elastic arteries, particularly the aorta. The inflammatory response to the spirochetes causes an obliterative endarteritis of the vaso vasorum, leading to a loss of blood supply to the elastic tunica media. Ischemia of the tunica media, combined with further syphilitic invasion into the tunica media itself, results in medial destruction and weakening, ultimately causing dilation and aneurysm-formation. Fibrosis of the vascular wall can give involved vessels a 'tree-bark'-like appearance and probably protects against aortic dissections which are not a consequence of syphilitic aneurysms.
- Syphilitic Aneurysms almost always involve the ascending aorta or aortic root and can lead to aortic regurgitation due to separation of the aortic valve leaflets. This is in contrast to atherosclerotic aneurysms which rarely involve the thoracic aorta and never the aortic root.