High-flow, aortocaval fistulae: radiologic and histopathologic evaluation in a rat model.

An animal model for a high-flow, aorta-to-vena cava fistula has been developed using microsurgical techniques in the rat. This model provides a means for histopathologic and angiographic evaluation of the natural evolution of major vessel, artery to vein fistulae. Data obtained from such a model may have relevance to the successful treatment of high-flow, head and neck fistulae using detachable intraarterial occlusive balloons. This microsurgical technique is unique, since it requires no intervening sutures or graft material that would alter the histopathologic process. After a series of such aortocaval fistulae were created, serial histologic and angiographic features were elucidated for intervals between 1 day and 6 months. Three stages of evolution are noted including: an initial hemorrhagic dissection phase; a subacute phase where organization of the thrombus and actual formation of a fistulous tract occurs; and a chronic phase characterized by pseudoaneurysm formation, arterialization of the vena cava, and proximal vasodilatation of the aorta.