Evaluation of the Valiant Mona LSA Thoracic Stent Graft System in Thoracic Aortic Aneurysms and Chronic Dissections

Inclusion Criteria: * Subject is at least 18 years of age. * Subject understands and has signed an Informed Consent * Subject must be considered a candidate for revascularization of the LSA. * Subject must be able to tolerate a surgical revascularization of the LSA. * Subject has a descending thoracic aneurysm (DTA) which will require coverage of the LSA * Subject has a healthy, non-diseased aortic proximal seal zone of at least 10 mm from the left carotid to the LSA and at least 5 mm landing zone distal to the LSA and proximal to the start of the aneurysm/ulcer/or the proximal entry tear for dissection. * Subject has a non-diseased aortic diameter between 25 mm and 42 mm (fusiform/saccular aneurysms or penetrating ulcers) or 28 mm to 44 mm (chronic type B dissections), * Subject has a LSA with a diameter between 8 mm and 13 mm. * Subject has sufficient landing zone within the LSA to accommodate the BSG without occlusion of any significant vessels * Subject has patent brachial arteries, iliac or femoral arteries (without circumferential calcifications and a diameter of ≥ 10mm), or can tolerate a conduit that will allow endovascular access to the aneurysmal site with the delivery system of the appropriate sized device chosen for treatment. * Subject has a condition requiring prospective revascularization of the LSA Exclusion Criteria: * Subject has an aneurysmal, tortuous, or atherosclerotic LSA, conflicting the branch graft insertion. * Subject has an aortic atheroma class…