Characterization of Subarachnoid Hyperdensities After Thrombectomy for Acute Stroke Using Dual-Energy CT

Background and Objectives: The presence of post-interventional subarachnoid hyperdensities (SA-HD) is a relatively common finding after mechanical thrombectomy (MT). We aimed to assess the incidence, characteristics, clinical relevance and predictors of SA-HD after MT as categorized through the use of post-interventional Dual Energy-CT (DE-CT). Methods: A single-center consecutive series of acute stroke patients treated with MT were retrospectively reviewed. Post-treatment SA-HD were defined as incident extra-axial hyperdensities in a follow-up DE-CT performed within a median of 8 hours after MT. SA-HD were further classified according to their content (isolated contrast extravasation versus blood extravasation) and extension [diffuse (hyperdensities in more than one extraparenchymal compartments) versus non-diffuse]. Adjusted logistic regression models assessed the association of SA-HD with pretreatment and procedural variables and with bad clinical outcome (shift towards worse categories in the ordinal Rankin Scale at 90 days). Results: SA-HD were observed in 120 (28%) of the 424 included patients (isolated contrast extravasation n=22, blood extravasation n=98). In this group, SA-HD were diffuse in 72 (60%) patients (isolated contrast extravasation n=7, blood extravasation n=65) and non-diffuse in 48 (40%) patients (isolated contrast extravasation n=15, blood extravasation n=33). Diffuse SA-HD were significantly associated with worse clinical outcome in adjusted models (cOR=2.3, 95%CI=1.36-4.00, p=0.002), unlike the specific SA-HD content alone. In contrast with the absence of SA-HD, only the diffuse pattern with blood extravasation was significantly associated with worse clinical outcome (cOR=2.4, 95%CI=1.36-4.15, p=0.002). Diffuse SA-HD patterns were predicted by M2 occlusions, more thrombectomy passes and concurrent parenchymal hematomas. Discussion: In our cohort of patients imaged within a median of 8 hours after MT, post-interventional SA-HD showed a diffuse pattern in 17% of thrombectomies and were associated with more arduous procedures. Diffuse SA-HD but not local collections of blood or contrast extravasations were associated with an increased risk of poor outcome and death. These findings reinforce the need for improvement in reperfusion strategies. Classification of Evidence: This study provides Class II evidence that in individuals with proximal carotid artery territory occlusions treated with mechanical thrombectomy, diffuse post-interventional subarachnoid hyperdensities on imaging 8 hours post-procedure are associated with worse clinical outcomes at 90 days.