Three patients with surgically inaccessible giant carotid
aneurysms/
pseudoaneurysms and one patient with
carotid cavernous fistula had endovascular occlusion with detachable
silicone balloons filled with
Cholografin. MR was performed before the procedures in three cases and again 18 hr to 44 days after embolization in all four cases. The age-related changes of arterial thrombi, as well as the optimal timing and value of different pulse sequences in the noninvasive follow-up, were evaluated. Arterial thrombi have some characteristics in common with intracerebral
hematomas, being isointense on T1-weighted spin-echo images during acute phase and subsequently acquiring hyperintense signals on both T1- and T2-weighted spin-echo images during the subacute and chronic phases. Additional observations are that (1) hyperacute (less than 24 hr old)
thrombus is hyperintense on T2-weighted spin-echo sequences; (2)
hemosiderin is less conspicuous in chronic intraluminal thrombi than in intracerebral
hematomas of comparable size; and (3)
thrombosis is initiated at a site remote from the apex of the
aneurysm and then progresses centripetally. The
Cholografin-filled balloon is hypointense to gray matter on T1-weighted spin-echo images and isointense to both hyperacute and chronic
thrombus on T2-weighted spin-echo images. The optimal timing and sequence for MR follow-up of a thrombosed
aneurysm with conventional spin-echo technique is beyond 7 days on T1-weighted spin-echo images. The in vivo appearance of
Cholografin-filled
silicone balloons does not change appreciably on T1- and T2-weighted spin-echo sequences up to 6 weeks if filled according to the manufacturer's specification.