Introduction/Purpose Acute tandem occlusions (TOs) are challenging to treat, and controversies exist regarding both the sequence of steps as well as how to handle the proximal occlusion in the acute setting. Although there is mounting evidence that acute carotid stenting is well tolerated, there are certain situations when the practitioner may be wary of acute stenting (e.g., bleeding concerns). The purpose of this study was to develop a Circle of Willis Score (COWS) to aid in this decision making.

Methods This is a retrospective review of TO patients from 2018 to 2022 treated in South Texas who had a persistent proximal occlusion following intervention (either expected or unexpected). Pre intervention CTA and intraoperative DSA were reviewed, and each patient was assigned a score 2 (complete COW), 1a (patent A1-Acomm-A1), 1p (patient Pcomm), or 0 (incompetent COW). Findings from the DSA took precedence over the CTA. Two cohorts were then created, COWS 2 versus COWS 1a/1p/0 combined. Angiographic outcomes were assessed using the mTICI score (successful reperfusion mTICI 2b-3) and clinical outcomes were assessed using discharge mRS (good outcome mRS 0-3)

Results Of 68 total TO cases, 12 had a persistent proximal occlusion. There were 5/12 (41.6%) patients in the COWS 2 cohort, 7/12 (58.4%) in the COWS 1a/1p/0 cohort (5/12 COWS 1a/1p and 2/12 COWS 0). In the COWS 2 cohort there were 2 ICA-ICA occlusions and 3 ICA-MCA occlusions. In the COWS 1a/1p/0 cohort there was one ICA-ICA occlusion and 6 ICA-MCA occlusions. LKW to puncture was shorter in the COWS 2 cohort (208 min vs. 464 min) but this was skewed by 2 patients in the COWS 1a/1p/0 cohort who had very long LKW-puncture times and both still had a good clinical outcome. Successful reperfusion was higher in the COWS 2 cohort (100% vs. 71%). Good clinical outcome was significantly higher in the COWS 2 cohort (80% vs 29%). When excluding the 2 patients in the COWS 1a/1p/0 cohort who had unsuccessful reperfusion (both of whom who happened to be COWS 0), good clinical outcome was still higher in the COWS 2 cohort (80% vs 40%).

Conclusion The COWS is a simple score that can be quickly applied using pre-intervention CTA and intraoperative DSA and may help practitioners predict a successful clinical outcome without proximal revascularization if there are concerns about performing an acute carotid stent during TO treatment. A completely patent COW may prevent a poor outcome with a persistent extracranial ICA occlusion. Future studies with larger sample sizes of patients are warranted to further understand the significance of intact collateral circulation in the circle of Willis when treating TOs.

Disclosures S. Pathuri: None. W. Johnson: None. M. Webb: None. T. Fielder: None. F. Al-Saiegh: None. P. Rodriguez: None. L. Birnbaum: None. J. Mascitelli: None.