ABSTRACT
Introduction: There are several factors to consider in the pathophysiology of aortic
dissection, including: hemodynamic disorders and factors related to the mechanical properties
and geometry of the aortic wall. The Vasa Vasorum (VV) seems to have an important role in
various diseases, since insufficient blood flow through VV is involved in the pathophysiology
of atherosclerosis and may contribute to necrosis of the media. Objective: To demonstrate the
histological alterations that occur in aortic wall over the long term, i.e. more than two weeks
after the interruption of blood flow through the VV of the descending aorta in a porcine
model. Method: The experiment was conducted with eight young female pigs, resulting from
the crossing of two breeds, Landrace and Large White, with a mean age of 8 weeks, weighing
on average 25 kg (21 - 27 kg). Through a left thoracoabdominal incision through the 6th
intercostal space, the adventitia was incised transversely in about one third of the
circumference of the aorta. The intercostal arteries were then ligated and an area of the
adventitia about 5 cm in length was removed from the middle portion of the descending aorta.
Then, the area from which the tunica adventitia had been removed, was wrapped in bovine
pericardium, after which the chest cavity was closed. Following euthanasia, at two, four, six
and eight weeks, the aortic segment wrapped in pericardium was removed together with
portions about 5 cm long of proximal and distal aorta. Next, slices from each segment
(proximal, middle and distal) of the aorta were stained with hematoxylin and eosin (HE) and
Weigert - Van Gieson method for elastic fiber staining. Results: After two weeks,
subendothelial fibrosis was observed with preservation of the internal elastic lamina and the
inner 2/3 of the tunica media. There was a slight cellular breakdown in the outer 1/3 of the
media with some lymphocyte and neutrophil infiltration. In addition, foci of angiogenesis
were identified in the outer 1/3 of the tunica media. In animals sacrificed at four weeks,
persisted a subendothelial fibrosis with preservation of the internal elastic lamina and of inner
1/3 of the tunica media. There was structural breakdown of elastic fibers and collagen fibers
in the outer 2/3 of the tunica media. Regarding inflammation, lymphocyte and neutrophil
infiltration was observed in the outer 2/3 of the tunica media. Foci of angiogenesis were
observed in the outer 2/3 of the tunica media. After six weeks, there was necrosis of the aortic
wall with subendothelial fibrosis. Regarding inflammation, there was lymphocytic, histiocytic
and neutrophil infiltration with necrosis throughout the media. Foci of angiogenesis were
observed throughout the tunica media and in the subendothelial portion. Finally, after eight
weeks, there was fibrosis of the entire wall of the aorta with destruction of the internal elastic
lamina. We observed an area of moderate inflammation near the endothelium. In relation to
angiogenesis, foci were observed throughout the tunica media and in the subendothelial
portion. Conclusion: Our study confirms that the ischemia induced by complete interruption
of blood flow through the vasa vasorum (VV) leads to degeneration of the media, determining
loss of normal structure of the aortic wall that is variable in its location, intensity and shape,
depending on the length and duration of the ischemic insult. In summary, we studied the
histological changes caused by the interruption of the VV of the descending aorta in pigs from
the second week of the injury until the occurrence of complete fibrosis of the wall at eight
weeks. This study may contribute to a better understanding of the role of VV in the
degeneration of the aortic wall and the mechanisms involved in aortic dissection.
Keywords: Aorta, Vasa Vasorum, Microcirculation, Ischemia and Dissection.