Syphilitic aneurysm mostly involves

Syphilitic Aneurysms arise during teiary syphilis due to chronic inflammation in the tunica adventitia of large elastic aeries, paicularly the aoa. The inflammatory response to the spirochetes causes an obliterative endaeritis of the vaso vasorum, leading to a loss of blood supply to the elastic tunica media. Ischemia of the tunica media, combined with fuher 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 aoic dissections which are not a consequence of syphilitic aneurysms. Syphilitic Aneurysms almost always involve the ascending aoa or aoic root and can lead to aoic regurgitation due to separation of the aoic valve leaflets. This is in contrast to atherosclerotic aneurysms which rarely involve the thoracic aoa and never the aoic root.