Arterial blocks were fixed in 10% formalin for at least 24 h and then prepared for routine light microscopy, as follows: gradual and increasing dehydration with 70% alcohol until absolute alcohol concentration was reached; diaphonization in xylene and liquid paraffin embedding at 60°C; and preparation of paraffin blocks. The paraffin blocks were cut with a microtome in a thickness of 3 µm, and the sections were mounted on extrafine glass slides (76´ 25 mm). Next, they were stained with hematoxylineosin for general morphology study; Verhoeff's stain for the evaluation of elastic fibers; and Masson's trichrome stain for general morphological study and characterization of elastic fibers, collagen, and muscle. Then, they were mounted with coverslips and natural resin. Also, immunohistochemistry assays were performed with the monoclonal HHF35 antibody (Kit DAKO Monoclonal Mouse anti-human Muscle Actin, clone HHF35) for determining the invasive reactions in the artery layers (smooth muscle), and C4d (Kit Spring Bioscience Rabbit Antihuman C4d Polyclonal antibody) to study the immune response in the vascular endothelium; in both immunohistochemistry tests, peroxidase was used as a developer. The slides were prepared and examined under magnifications of 2.5´, 10´, and 40´ by a duly accredited pathologist.