Three patients are described with unruptured large partially thrombosed aneurysms with a peculiar donut-shaped remaining lumen. Observations suggest that the flow geometry of the aneurysm and parent vessels induces a preferential circular laminar flow inside the aneurysm followed by partial intraluminal thrombosis leaving a donut-shaped lumen to accommodate the circular flow. This flow mechanism of thrombus formation inside aneurysms is different from the more common repeated intramural dissections and hemorrhages that cause growth in most large and giant partially thrombosed aneurysms.

Introduction: Pervious thrombi benefit more from intravenous thrombolysis, but the role of perviousness in endovascular treatment (EVT) is not completely clear. Thrombus length is negatively associated with outcome after EVT. Pervious, long thrombi may be more difficult to aspirate, or fragment more easily than non-pervious, short thrombi. We assessed the effect of perviousness and thrombus length on results of first-line aspiration thrombectomy in EVT, in comparison to stent-retrievers. Methods: We included MR CLEAN Registry patients (N=1526) with thin-slice imaging available, and aspiration or stent-retriever as first EVT attempt (N=391). Thrombus perviousness was measured by thrombus attenuation increase (Houndsfield Units; HU). Associations with 90-day modified Rankin Scale score (mRS), and final and first-pass reperfusion (eTICI 2B-3) were tested with adjusted logistic regression analyses. Results: Sixty-five (21%) patients were treated with first-line aspiration, 252 (79%) with stent-retrievers. Perviousness was not significantly associated with mRS after either first-line approach (Figure 1). Analysis per perviousness quartile did show improved mRS for stent-retrievers in the highest quartile only (>12.3 HU; acOR for mRS shift with stent-retriever treatment 3.08, 95%CI 1.06-8.96). Thrombus length was negatively associated with mRS after first-line stent-retriever thrombectomy (acOR 0.96, 95%CI 0.93-0.99). First-pass reperfusion and thrombus length were significantly, negatively associated in the first-line aspiration group (acOR 0.88, 95%CI 0.80-0.96). Conclusions: Patients with longer thrombi may show worse outcomes after both aspiration and stent-retriever thrombectomy. In patients with high perviousness values, stent-retriever thrombectomy may be related to improved outcomes as compared to first-line aspiration.