Abstract 1122‐000182: Histological Composition of Large Vessel Occlusion Stroke‐Causing Thrombi to Identify Etiologies: Systematic Review and Meta‐Analysis

Introduction : More than a third of large vessel occlusion ischemic strokes do not have clear etiology. Mechanical thrombectomy provides a method to retrieve stroke‐causing thrombi and potentially identifying the etiology. A systematic meta‐analysis is performed to determine if there is a histological difference in red blood cell (RBC) composition of thrombi after the etiology of the stroke is known. Methods : We performed a systematic search through PUBMED and EMBASE. Studies meeting inclusion criteria were identified in which the large vessel occlusion stroke‐causing thrombi histology and etiology of the stroke were determined as either large artery atherosclerotic (LAA), cardioembolic (CE) or cryptogenic. Studies that had the data available or extractable data were selected. Random‐effect models were used to compare the histological difference between each etiology. Results : From inception to August 2021, 4 studies (n = 1022) were used to compare CE vs LAA, 5 studies (n = 1247) were used to compare CE vs cryptogenic and 4 studies (n = 654) were used to compare LAA vs cryptogenic. There was no significant difference in the red blood cells vs white blood cells/fibrin/platelets component between the stroke origins of CE vs LAA (mean difference (MD) ‐1.87; 95% confidence internal [CI]: ‐16.51, 12.78), CE vs cryptogenic (MD 1.18; 95% CI: ‐1.49, 3.86) and LAA vs cryptogenic (MD 7.20; 95% CI: ‐3.93, 18.34). Conclusions : There was no significant gross histological difference between CE, LAA and cryptogenic stroke etiologies and of the large vessel occlusion stroke‐causing thrombi retrieved by mechanical thrombectomy. Further studies into biochemical or genetic markers may be needed to identify stroke etiology.

Thymomas and Associated Hyperplastic Lesions in Wistar Hannover Rats

Thymomas occur prevalently in aged Wistar Hannover (WH) rats, along with hyperplastic lesions that cannot be categorized as thymomas. We compared the histological features of hyperplastic lesions and thymomas in WH rats, the incidences of these lesions, and the relationship of these lesions to the degree of thymic involution and also compared these lesions with those of Sprague Dawley (SD) rats in 4-, 13-, 26-, and 104-week studies. There were no morphological differences between hyperplastic cells and benign tumor cells in thymomas. The histological difference between hyperplastic lesions and thymomas was the size of the proliferative areas and the number of medullary differentiation areas. The hyperplastic lesions of the thymus in WH rats might have a potential for progression to thymomas due to the observed multiple hyperplastic lesions or mixed lesions with thymomas. The incidence of these proliferative lesions in the thymus was higher in females than in males. Further, the incidence of these proliferative lesions was higher in WH rats than in SD rats. Thymic involution was more severe in males than in females and more severe in SD rats than in WH rats. The differences in involution progression may have been reflected in the incidence of thymic proliferative lesions in SD and WH rats.