Histopathologic characteristics of a chronic arteriovenous malformation ina swine model: Preliminary study

BACKGROUND AND PURPOSE: The experimental induction of histologic transforma tions in microvessels of similar caliber to those of nidus vessels of cereb ral arteriovenous malformations (AVMs) has not been attempted previously, O ur goal was to examine preliminarily the histopathologic characteristics of nidus vessels and the angiographic features of a chronic AVM model in swin e, METHODS: AVM models were fashioned from bilateral carotid retia mirabilia o f seven swine after the surgical formation of large unilateral carotid-jugu lar fistulas, One AVM model was made for immediate use, whereas in the othe r six, follow-up angiography was obtained at varying intervals (2 to 180 da ys) after model creation, Light and electron microscopy, immunohistochemist ry (using monoclonal antibodies against smooth muscle actin and PC10 agains t proliferating cell nuclear antigen), and histometry were performed on the nidus vessels of three swine: one acutely created, one 2 months old, and o ne 6 months old, RESULTS: Vascular dilatation and tortuosity of the main arterial feeder and draining vein were evident angiographically as early as 4 days after AVM c reation, and were maximal in the 6-month-old model, Compared with the acute ly created nidus vessels, those in the two chronic models revealed disrupte d and attenuated elastica and intimal hyperplasia that was focal ("cushions ") or generalized, leading to luminal occlusion, Variable numbers of cells in the tunica media of chronic nidus vessels contained smooth muscle actin, PC10/proliferating cell nuclear antigen immunoreactivity was observed in t he endothelium and subendothelial layers, Histometry showed increases in in timal hyperplasia and medial thickness in the chronic vessels, CONCLUSION: Nidus vessels in this chronic swine AVM model exhibited strikin g histologic changes similar to those seen in cerebral AVMs, The induced ve ssel growth seen angiographically and histologically in components of the c hronic AVMs was consistent with the presence of persistently raised intrava scular hemodynamic loads, This preliminary feasibility study suggests that the realistic histologic characteristics of this chronic AVM model are an a ttractive feature, and if confirmed in future, more comprehensive, studies would be of benefit in accurate histopathologic interpretation of the effec ts of superimposed experimental embolotherapy or radiosurgery, This model m ay provide a useful experimental tool to study the dynamic cellular and tis sue events that dictate the development and natural history of AVMs.