Large hemorrhagic conversion following reperfusion in a patient with distal left internal carotid occlusion with poor pial collateral formation. Large hemorrhagic conversion following reperfusion in a patient with distal left internal carotid occlusion with poor pial collateral formation. A, Left internal carotid arteriogram demonstrates a distal carotid internal occlusion (arrow) with refluxed contrast filling of the occipital artery (arrowhead, A). B–E, Arteriograms of the right internal carotid (B and C) and left vertebral arteries (D and E) demonstrate no circle of Willis collaterals on either the late arterial phase (arrowheads, B and D) or the late venous phase (arrowheads, C and E). Poor pial collateral formation reconstitutes, at best, the M4 branches of the MCA (arrowheads, D and E). F and G, Twenty-four hours following reperfusion (F), the patient experienced a large hemorrhage (G) and subsequently died. G.A. Christoforidis et al. AJNR Am J Neuroradiol 2009;30:165-170 ©2009 by American Society of Neuroradiology