Rabbit aneurysm models mimic histologic wall types identified in human intracranial aneurysms

Background Semiquantitative scales correlate histopathologic findings in the walls of human aneurysms with rupture status. Objective To apply a semiquantitative scale to the rabbit elastase-induced aneurysm model to determine whether rabbit histologic types mimic the full range of histologic subtypes of humans. Materials and methods Twenty-seven elastase-induced female rabbit aneurysms were studied, harvested at 2 weeks (n=5) and 12 weeks (n=22). Paraffin-embedded sections received hematoxylin-eosin and Verhoeff-Van Gieson staining. Immunohistochemistry was performed for α-smooth muscle actin and CD31 for endothelial cells. A semiquantitative scale was used for scoring based on human aneurysm tissue, divided into four subtypes according to cellular and extracellular matrix findings: Type A, linear organized smooth muscle cells (SMCs) and intact endothelium; type B, thickened wall with disorganized, proliferating SMCs; type C, thick, collagenized and hypocellular wall with or without organizing thrombosis, and type D, extremely thin, hypocellular wall. Separate scoring was performed of the aneurysm neck and proximal and distal zones. Results Findings compatible with all subtypes of human aneurysm tissue were identified. Types A and C were found in 13 (48%) and 11 (41%) of 27 aneurysms and in the proximal and distal wall at both time points. Type B was found in 16 aneurysms (59%), exclusively at the neck at both time points; type D, in 14 aneurysms (52%), exclusively at proximal and distal zones of 12-week aneurysms. Conclusions The wall of elastase-induced rabbit aneurysm demonstrates histologic findings similar to the four categories of human cerebral aneurysms based on cellular and extracellular wall content.