The nature of early intraluminal thrombosis in terminal aneurysms occluded with guglielmi detachable coils.

To investigate the early intraluminal thrombotic events after endovascular treatment of terminal aneurysms with detachable coils, and to assess the biological changes over the first three weeks, terminal arterial bifurcation aneurysms were produced microsurgically in 20 rabbits. After a healing period of three weeks, transfemoral angiography was performed and all aneurysms were occluded with Guglielmi Detachable Coils (GDC). Complete (i.e. 100%) occlusion was achieved in ten aneurysms. About 95% occlusion (only a small neck remnant) was seen in eight cases. In two cases, occlusion was about 70 - 80%. Half of the animals were treated by anticoagulation during and continuously two days after occlusion therapy. Angiographic studies and histological analysis were done for four aneurysms (two without and two with anticoagulation) after 24 - 48 hours, 3 - 4 days, 6 - 7 days, 14 days, and 21 days after the treatment. On macroscopic examination, complete occlusion of the aneurysms by early thrombus formation was found in all cases during the first two days. After three to seven days, recanalization and fibrinolysis were observed, leading to a reopening of the neck, and part of the dome. After three weeks recanalization was found in six out of eight aneurysms, regardless of whether the animal was under anticoagulation. In nine cases, the degree of occlusion was overestimated by angiography compared to the pathological findings. During the early phase after occlusion of an aneurysm with platinum coils, extensive clot formation is induced. Over time due to the natural fibrinolysis, continuous recanalization beginning at the neck takes place. These findings can explain the clinical phenomenon of early thromboembolic complications, and the reopening and regrowth of aneurysms occluded with metallic coils observed at later stages.