A New Morphological Variant of Acute Aortic Dissection, Non-A-Non-B Type: Choosing Treatment Strategy

Abstract

Treatment of acute aortic dissection is determined by the Stanford classification which classifies all cases as type A requiring emergency surgery, and type B managed with antihypertensive therapy, and, more recently, endovascular aneurysm repair. Owing to the introduction of computed tomography (CT) and magnetic resonance imaging (MRI), a new morphological type of the disease has been identified, in which the dissection starts from the aortic arch or the first part of the descending thoracic aorta and spreads retrogradely. A new classification of acute aortic dissection – TEM (T – type, E – entry, M – malperfusion), distinguishes 3 morphological variants of the disease: type A, type B, and non-A-non-B type.
 The frequency of non-A-non-B type among the other forms of acute aortic dissection is 11%. The existing classifications contain no guidelines on the management of a dissection that starts from or is limited to the aortic arch.
 The aim. To outline the morphological characteristics of a new, non-A-non-B type of aortic dissection, and to determine acceptable criteria for choosing surgical procedure based on the literature review and 2 observed clinical cases.
 Material and methods. During 2016-2020, two patients were classified as those having acute non-A-non-B type aortic dissection. Both patients underwent emergency surgery with total aortic arch replacement by a linear graft in one case and by a multi-branch one in the other. The patients were discharged on day 15 and 21 after surgery, respectively, without signs of heart failure or malperfusion, and with healed wounds. In neither of them a complete obliteration of the false lumen of the aorta was achieved; however, the first patient showed marked decrease in the total diameter of the descending thoracic aorta, as well as alleviation of the numbness in the right leg. The expediency of the operation in this type of dissection is explained by the fact that this morphological variant is presumably a local expansion of the type B dissection, the procedure defined as conservative by the Stanford classification. At the same time, the retrograde spreading of the dissection to the arch presents a risk of further involvement of the ascending aorta, which is another indication for surgery. Another variant of acute aortic dissection, which is morphologically similar to the non-A-non-B type, is the retrograde type A, in which surgical treatment is mostly recommended.
 Conclusions. The non-A-non-B type is one of the morphological variants of acute aortic dissection which is mainly subject to emergency surgery due to the risk of potentially fatal complications. Endovascular aneurysm repair of the entire aortic arch in the non-A-non-B type aims to eliminate the initial tear of the intima. If the intimal tear is located below the orifice of the left subclavian artery, prosthetics of an arch should be supplemented with endovascular repair of the descending aorta.