Early histological changes in the aortic media after thoracic endovascular stent grafting (TEVAR)

Objective: Thoracic endovascular repair (TEVAR) has emerged as an alternative to open surgery in the descending thoracic aorta, although complication and reintervention rates remain high. Reports of structural changes in the aortic wall are rare. Herein we describe our histological findings 5 days after TEVAR in a porcine model.

Methods: Two overlapping stent grafts (Gore Excluder AAA, contralateral leg endoprosthesis) were implanted in each of 6 juvenile pigs, covering the entire descending thoracic aorta. Five days after stent placement, 2 tissue samples were taken from the proximal and distal landing zones in each pig: one in an area covered by the stent, and the other just beyond it proximally or distally. Additional samples were taken from the overlap zone of the stents, from the unstented proximal and distal aorta, and from 6 native porcine aortas. Medial thickness was measured between the innermost and outermost elastin layers in digital images of van Giesson-stained sections. Medial necrosis was quantified on H&E sections. Statistical comparisons used the Wilcoxon or Kruskal-Wallis tests.

Results: Significant medial thinning was always observed in the region covered by the stent. At the proximal landing zone, aortic wall thickness changed from 1387±68µm to 782±74µm within the stent (p=0.028), and at the distal landing site from 365±67µm within the stent to 501±57µm distally (p=0.028). In the region of overlap, the aortic wall measured 524±122µm versus 1053±77µm in native controls (p=0.004). Aortic thickness proximal to the graft did not differ from the proximal region of native aortas (1468±96 versus 1513±80µm, p=0.423), but the aorta was significantly thinner distal to the stent (707±38 versus 815±52µm, p=0.004). Laminar necrosis constituted 38±6.5% of the media in the proximal landing zone, 54±3.7% in the overlap zone, and 46±12.8% in the distal landing zone. In all stent-covered regions, elastic and collagen fibers were stretched and had lost their wave-like structure, although elastic fibers were not fragmented. In 5 aortas, inflammatory infiltration was seen within the media, and in one, an early intimal foreign body reaction.

Conclusion: We found significant medial thinning and necrosis of the stented aorta, as well as thinning of the aorta distally, 5 days after TEVAR in pigs. This suggests an early phase of vulnerability to rupture after stenting, before scarring and adaptive changes have strengthened the residual aorta.