Endovascular Treatment of Chronic Type B Aortic Dissection
The optimal management of descending aortic dissection is controversial. Even though medical therapy demonstrated some early survival benefit with respect to surgical repair, no significant difference in long term outcome has been demonstrated.
Mortality is related either to retrograde progression of dissection with involvement of the proximal aorta or to expansion of the false lumen and formation of a thoracic aneurysm. Several reports in the literature analysed long-term outcome in patients with type B dissection, comparing medical with surgical therapy without evidence of a significant difference between the two groups. Five-year survival rates between 32%–72% have been reported because medical therapy alone cannot prevent the evolutive course of the disease. Recently, the development of endovas-cular therapy offers additional opportunity in the treatment of type B dissection as potential alternative to medical therapy and open surgical repair. The rationale of endovascular treatment of aortic dissection was originally based on evidence in the literature of protective effect of false lumen thrombosis against false lumen expansion and on the clinical observation that patients in the rare instance of spontaneous thrombosis of the false lumen have a better long-term prognosis than without it. Conversely, persistent perfusion of the false lumen has been identified as an independent predictor of progressive aortic enlargement and adverse long-term outcome. Closure of the entry tear of a type B dissection may promote both depres-surisation and shrinkage of the false lumen, with subsequent thrombosis, fibrous transformation, remodelling and stabilization of the aorta. Published data confirm the technical feasibility and a relative low rate of complications with respect to surgical repair. However long-term follow-up and outcome information, in order to document the sustained benefit of endovascular repair, are still limited. With growing experience in endovascular stent-graft treatment, the spectrum of acute and midterm complications has broadened to include potentially disastrous events. Late aneurismal degeneration of the thrombosed false lumen has been reported, and also several case reports have highlighted the risk of retrograde extension of the dissection into the ascending aorta, potentially caused by stent-graft induced intimal injury. Even though extension of dissection is known event in the course of type B dissection disease, wire or sheath manipulation during the endovascu-lar procedure could increase the risk of this dreadful complication. Continuous progress in stent-graft technology, improving morphology and flexibility, may lead to more suitable stent-graft configuration for aortic dissection. However, these unexpected complications underline the particular fragility of the aortic wall and the need of careful selection criteria and rigorous follow-up. Before the responses of controlled rando mized trials it will be difficult to provide certainties on which is the best timing and treatment modality with respect to acute and chronic forms.