Stroke endovascular thrombectomy related subarachnoid hyperdensity: incidence, predictive factors, and a proposed sub-classification.

Background: Subarachnoid hyperdensity (SAH) after endovascular thrombectomy is a well-known phenomenon. Nevertheless, the clinical significance and natural history of this phenomenon is not well described. In addition, we test previously postulated hypotheses of distal occlusions sites and antithrombotic use to SAH prevalence and extent.

Methods: We performed a retrospective analysis of all patients presenting with acute stroke and treated by endovascular thrmbectomy in our tertiary center January 2016 and February 2021. Only patients who underwent CT scan of the brain within 24 h after procedure were included.

Results: 394 patients were included in this study. SAH after EVT was evident on CT in18.3% of those. Most of these (10.7%), had non-resolving hyperdensity (persistent SAH) on follow up imaging. A minority (2.6%) had resolving hyperdensity (transient SAH). Only 2% had a combination of subarachnoid hyperdensity and intracerebral hemorrhage (SAH + ICH). Transient and persistent SAH were associated with good functional and imaging outcomes as compared to SAH + ICH patients. Older age, large infarct size, stentretriever use and partial recanalization were correlated with SAH + ICH. Distal occlusions and distal vessel angulations resulting in higher traction potential were more prevalent in persistent SAH group. Higher number of thrombectomy passes was correlated with the extent of persistent SAH. Transient SAH group did not show statistically significant demographic or procedural trends.

Discussion: We propose therefore a distinct classification of the post thrombectomy SAH subtypes and discuss the putative pathophysiological mechanisms of the three distinct phenomena and their predictive factors.