J Korean Med Sci.  2012 Oct;27(10):1170-1176. 10.3346/jkms.2012.27.10.1170.

Tissue Responses to Endovascular Stent Grafts for Saccular Abdominal Aortic Aneurysms in a Canine Model

• Kim HB
• Choi YH
• So YH
• Min SK
• Kim HC
• Kim YI
• Park JH
• Chung JW

• KMID: 1778822
• DOI: http://doi.org/10.3346/jkms.2012.27.10.1170

Abstract

We investigated tissue responses to endoskeleton stent grafts for saccular abdominal aortic aneurysms (AAAs) in canines. Saccular AAAs were made with Dacron patch in 8 dogs, and were excluded by endoskeleton stent grafts composed of nitinol stent and expanded polytetrafluoroethylene graft. Animals were sacrificed at 2 months (Group 1; n = 3) or 6 months (Group 2; n = 5) after the placement, respectively. The aortas embedding stent grafts were excised en bloc for gross inspection and sliced at 5 to 8 mm intervals for histopathologic evaluation. Stent grafts were patent in all except a dog showing a thrombotic occlusion in Group 2. In the 7 dogs with patent lumen, the graft overhanging the saccular aneurysm was covered by thick or thin thrombi with no endothelial layer, and the graft over the aortic wall was completely covered by neointima with an endothelial layer. Transgraft cell migration was less active at an aneurysm than at adjacent normal aorta. In conclusion, endoskeleton stent grafts over saccular aneurysms show no endothelial coverage and poor transgraft cell migration in a canine model.

Keyword

Aorta; Aortic aneurysm; Prostheses; Endothelial cells

MeSH Terms

Alloys/chemistry
Angiography
Animals
Aortic Aneurysm, Abdominal/*pathology/surgery/ultrasonography
Cell Movement
Disease Models, Animal
Dogs
Endothelial Cells/cytology
Neointima/etiology
Polytetrafluoroethylene/chemistry
*Stents
Thrombosis/etiology
Tomography, X-Ray Computed
Alloys
Polytetrafluoroethylene

Figure

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  Fig. 1 An aneurysm model and an endoskeleton stent graft. (A) An abdominal aortic aneurysm is shown in CT angiography a week after laparotomy. (B, C) A self-expandable nitinol stent (B) is covered with ePTFE (C).

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  Fig. 2 Schematic division of the aorta. The aortic specimen with a stent graft was artificially divided into 6 segments for the histologic evaluation; proximal normal aortic segment with bare stent (PS), proximal normal aortic segment with stent graft (PG), aneurysmal side of the aortic segment of saccular aneurysm (AN) and anti-aneurysmal side of the aortic segment of saccular aneurysm (A-AN), distal normal aortic segment with stent graft (DG), and distal normal aortic segment with bare stent (DS). S, stent; SG, stent graft; Ao, aorta; P, proximal; D, distal.

• 

  Fig. 3 Follow-up imaging after endovascular grafting. Thick tissue formation (arrow) and crescentic low attenuation at AN are demonstrated in conventional (A) and CT (B) angiography 6 months after grafting.

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  Fig. 4 Morphometric analysis of neointima. There is a lack of glossy white neointimal coverage at AN (A). Glossy white neointimal coverage is demonstrated in 91% of the inner surface of the stent graft where there is a layer of endothelium on microscopic inspection (B).

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  Fig. 5 Endothelialization of neointima. A layer of cells covers neointima in A-AN. The cells are strongly reactive to Factor VIII-related antigen and look brownish, which means they are endothelia (Factor VIII-related antigen immunohistochemical staining, original magnification × 400).

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  Fig. 6 Organization of thrombi. Relatively fresh thrombi (arrow) are seen along the inner surface of the stent graft in AN while organized thrombi (asterisk) are seen in the excluded saccular aneurysm (Masson trichrome stain, original magnification × 1).

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  Fig. 7 Transgraft cell migration. (A) Cross section of the aorta at the level of aneurysm sac (Masson trichrome stain, original magnification × 1). (B, C) Magnified views of the red rectangular block in (A). There are lots of collagen and numerous spindle cells (arrows) in the graft. It was rated as Grade 4. (D, E) Magnified views of the black rectangular block in (A). There are little collagen and no spindle cell in the graft. It was rated as Grade 1.

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