High thrombin-activatable fibrinolysis inhibitor expression in thrombi from stroke patients in elevated estrogen states.

BACKGROUND: The risk of acute ischemic stroke (AIS) associated with high estrogen states, including pregnant patients and those using oral contraceptives, has been well documented. We described the histological composition of thrombi collected in these cases. METHODS: From a prospective tissue registry (STRIP registry) of thrombi retrieved during mechanical thrombectomy for AIS, we identified 5 patients with high estrogen states: 1 post-partum patient, 1 undergoing hormone replacement therapy and 3 consuming oral contraceptive pills. Five male control patients were randomly chosen matched by age. Immunohistochemistry for CD42b (platelets), von Willebrand factor (vWF), thrombin-activatable fibrinolysis inhibitor (TAFI), fibrinogen and plasminogen activator inhibitor-1 (PAI-1) was performed. Expression was quantified using Orbit Image Software. Student's t-test was performed as appropriate. RESULTS: Mean TAFI content for the high estrogen state group was higher than controls (25.6 ± 11.9% versus 9.3 ± 9.0%, p = 0.043*). Mean platelet content for the high estrogen state group was lower than controls (41.7 ± 10.6% versus 61.8 ± 12.9%, p = 0.029*). No significant difference was found in vWF, fibrinogen and PAI-1 expression. Mean time to recanalize was higher in the high estrogen state group compared to the control group (57.8 ± 27.6 versus 22.6 ± 11.4 min, p = 0.0351*). The mean number of passes required was higher in the high estrogen group compared to controls 4.6 versus 1.2, p = 0.0261*). CONCLUSIONS: TAFI expression, a powerful driver of thrombosis, was significantly higher in stroke thrombi among patients with high estrogen states compared to controls.

Shell Versus Core Architecture and Biology of Thrombi in Acute Ischemic Stroke: A Systematic Review.

BACKGROUND: The presence of an outer shell has been recently described as a common feature of acute ischemic stroke (AIS) thrombi. We performed a systematic review of the current literature on shell genesis, structure, and clinical significance. METHODS: Following PRISMA guidelines, we searched Ovid Cochrane Central Register of Controlled Trials, Embase, Medline, Scopus, and Web of Science for studies reporting the composition and structure of AIS thrombi and clot analogs. Identified studies were added to Covidence software for primary screening. Two reviewers independently screened titles and abstracts followed by full-text screening. RESULTS: From 1290 identified studies, 10 were included in this review. Studies using histology/immunohistochemistry/immunofluorescence described fibrin, platelets, von Willebrand factor, and neutrophil extracellular traps as the main components of the shell. Scanning electron microscopy demonstrated a dense, compact fibrin/platelet-rich shell, and a core rich in polyhedrocytes. Microfluidics studies identified highly activated P-selectin-positive platelets and fibrin forming the core while secondary agonists adenosine diphosphate and thromboxane, along with loosely packed P-selectin-negative platelets constituted the shell. CONCLUSIONS: The composition, compaction, and integrity of the shell may impact thrombolysis and revascularization outcomes. The preponderance of studies supported this conclusion.

Histological evaluation of acute ischemic stroke thrombi may indicate the occurrence of vessel wall injury during mechanical thrombectomy.

BACKGROUND: Several animal studies have demonstrated that mechanical thrombectomy (MT) for acute ischemic stroke (AIS) may cause vessel wall injury (VWI). However, the histological changes in human cerebral arteries following MT are difficult to determine. OBJECTIVE: To investigate the occurrence of VWI during MT by histological and immunohistochemical evaluation of AIS clots. METHODS: As part of the multicenter STRIP registry, 277 clots from 237 patients were analyzed using Martius Scarlett Blue stain and immunohistochemistry for CD34 (endothelial cells) and smooth muscle actin (smooth muscle cells). RESULTS: MT devices used were aspiration catheters (100 cases), stentriever (101 cases), and both (36 cases). VWI was found in 33/277 clots (12%). There was no significant correlation between VWI and MT device. The degree of damage varied from grade I (mild intimal damage, 24 clots), to grade II (relevant intimal and subintimal damage, 3 clots), and III (severe injury, 6 clots). VWI clots contained significantly more erythrocytes (p=0.006*) and less platelets/other (p=0.005*) than non-VWI clots suggesting soft thrombus material.Thrombolysis correlated with a lower rate of VWI (p=0.04*). VWI cases showed a significantly higher number of passes (2 [1-4] vs 1 [1-3], p=0.028*) and poorer recanalization outcome (p=0.01*) than cases without VWI. CONCLUSIONS: Histological markers of VWI were present in 12% of AIS thrombi, suggesting that VWI might be related to MT. VWI was associated with soft thrombus consistency, higher number of passes and poorer revascularization outcome. There was no significant correlation between VWI and MT device.

Neurologic Effects of Gadolinium Retention in the Brain after Gadolinium-based Contrast Agent Administration.

Background Concerns over the neurotoxic potential of retained gadolinium in brain tissues after intravenous gadolinium-based contrast agent (GBCA) administration have led to pronounced worldwide use changes, yet the clinical sequelae of gadolinium retention remain undefined. Purpose To assess clinical and neurologic effects and potential neurotoxicity of gadolinium retention in rats after administration of various GBCAs. Materials and Methods From March 2017 through July 2018, 183 male Wistar rats received 20 intravenous injections of 2.5 mmol per kilogram of body weight (80 human equivalent doses) of various GBCAs (gadodiamide, gadobenate, gadopentetate, gadoxetate, gadobutrol, gadoterate, and gadoteridol) or saline over 4 weeks. Rats were evaluated 6 and 34 weeks after injection with five behavioral tests, and inductively coupled plasma mass spectrometry, transmission electron microscopy, and histopathology were performed on urine, serum, cerebrospinal fluid (CSF), basal ganglia, dentate nucleus, and kidney samples. Dunnett post hoc test and Wilcoxon rank sum test were used to compare differences between treatment groups. Results No evidence of differences in any behavioral test was observed between GBCA-exposed rats and control animals at either 6 or 34 weeks (P = .08 to P = .99). Gadolinium concentrations in both neuroanatomic locations were higher in linear GBCA-exposed rats than macrocyclic GBCA-exposed rats at 6 and 34 weeks (P < .001). Gadolinium clearance over time varied among GBCAs, with gadobutrol having the largest clearance (median: 62% for basal ganglia, 70% for dentate) and gadodiamide having no substantial clearance. At 34 weeks, gadolinium was largely cleared from the CSF and serum of gadodiamide-, gadobenate-, gadoterate-, and gadobutrol-exposed rats, especially for the macrocyclic agents (range: 70%-98% removal for CSF, 34%-94% removal for serum), and was nearly completely removed from urine (range: 96%-99% removal). Transmission electron microscopy was used to detect gadolinium foci in linear GBCA-exposed brain tissue, but no histopathologic differences were observed for any GBCA. Conclusion In this rat model, no clinical evidence of neurotoxicity was observed after exposure to linear and macrocyclic gadolinium-based contrast agents at supradiagnostic doses. © RSNA, 2022 Online supplemental material is available for this article.

High-resolution scanning electron microscopy for the analysis of three-dimensional ultrastructure of clots in acute ischemic stroke.

BACKGROUND: Characterization of acute ischemic stroke (AIS) clots has typically focused on two-dimensional histological analysis of the thrombus. The three-dimensional (3D) architecture and distribution of components within emboli have not been fully investigated. The aim of this study was to examine the composition and microstructure of AIS clots using histology and serial block-face scanning electron microscopy (SBFSEM). METHODS: As part of the multi-institutional STRIP registry, 10 consecutive AIS emboli were collected from 10 patients treated by mechanical thrombectomy. Histological and immunohistochemical analysis was performed to determine clot composition. SBFSEM was used to assess the ultrastructural organization of the clots and specific features of individual components. RESULTS: Quantification of Martius Scarlett Blue stain identified fibrin (44.4%) and red blood cells (RBCs, 32.6%) as the main components. Immunohistochemistry showed a mean platelet and von Willebrand factor content of 23.9% and 11.8%, respectively. The 3D organization of emboli varied greatly depending on the region analyzed. RBC-rich areas were composed mainly of tightly packed RBCs deformed into polyhedrocytes with scant fibrin fibers interwoven between cells. The regions with mixed composition showed thick fibrin fibers along with platelets, white blood cells and RBC clusters. Fibrin-rich areas contained dense fibrin masses with sparse RBC. In three cases, the fibrin formed a grid-like or a sponge-like pattern, likely due to thrombolytic treatment. Segmentation showed that fibrin fibers were thinner and less densely packed in these cases. CONCLUSIONS: 3D-SEM provides novel and potentially clinically relevant information on clot components and ultrastructure which may help to inform thrombolytic treatment and medical device design.

Characterization of thrombus composition with multimodality CT-based imaging: an in-vitro study.

BACKGROUND: CT is the most commonly used imaging modality for acute ischemic stroke evaluation. There is growing interest to use pre-operative imaging to characterize clot composition in stroke. We performed an in-vitro study examining the ability of various CT techniques in differentiation between different clot types. METHODS: Five clot types with varying fibrin and red blood cells (RBCs) densities (5% RBC and 95% fibrin; 25% RBC and 75% fibrin; 50% RBC and 50% fibrin; 75% RBC and 25% fibrin; 95% RBC and 5% fibrin) were prepared and scanned using various CT scanning protocols (single-energy, dual-energy, photon-counting detector CT, mixed images, and virtual monoenergetic images). Martius Scarlett Blue trichrome staining was performed to confirm the composition of each clot. Mean CT values of each type of clot under different scanning protocol were calculated and compared. RESULTS: Mean CT values of the CT numbers in the five clot specimens for 5%, 25%, and 50% RBC clot were similar across modalities, and increased significantly for 75% and 95% RBC clots (P<0.0001). Mean CT values are highest in the Mono +50 keV images in each type of clot, and they were also significantly higher than all other imaging protocols (P<0.001). Dual-energy CT with Mono +50 keV images showed the greatest difference between attenuation in each type of clot. CONCLUSION: Mono +50 keV dual-energy CT scan may be helpful for differentiating between RBC-rich and fibrin-rich thrombi seen in large-vessel occlusion patients.

Mechanism of Action and Biology of Flow Diverters in the Treatment of Intracranial Aneurysms.

Flow diverters have drastically changed the landscape of intracranial aneurysm treatment and are now considered first-line therapy for select lesions. Their mechanism of action relies on intrinsic alteration in hemodynamic parameters, both at the parent artery and within the aneurysm sac. Moreover, the device struts act as a nidus for endothelial cell growth across the aneurysm neck ultimately leading to aneurysm exclusion from the circulation. In silico computational analyses and investigations in preclinical animal models have provided valuable insights into the underlying biological basis for flow diverter therapy. Here, we review the present understanding pertaining to flow diverter biology and mechanisms of action, focusing on stent design, induction of intra-aneurysmal thrombosis, endothelialization, and alterations in hemodynamics.

Elastase-induced intracranial dolichoectasia model in mice.

BACKGROUND: Intracranial dolichoectasia is associated with high morbidity, and its pathophysiology remains poorly understood. OBJECTIVE: To develop a technique for the creation of a murine model of dolichoectasia. METHODS: C57/BL6 mice were injected with 0 milliunit (mu) (control, n = 5), 15 mu (n = 7), 25 mu (n = 10), 35 mu (n = 10), and 55 mu (n = 6) of elastase in the cisterna magna. Fourteen days after injection, the vasculature of the brain was perfused with MicroFil polymerizing compound. Tortuosity index and the percentage increase in arterial diameter were calculated for the basilar artery, posterior communicating arteries, and the A1 segment of the anterior cerebral arteries. Tortuosity index >10 combined with 25% increase in diameter were used to indicate success in achieving dolichoectasia. RESULTS: The mortality rate was 28%, 30%, 80%, and 83% in the 15, 25, 35, and 55 mu groups, respectively. As the 35 and 55 mu groups experienced unacceptable mortality rates, they were excluded from further analysis. The tortuosity index and percent increase arterial diameter of the 15 and 25 mu groups for the left anterior cerebral arteries, right anterior cerebral arteries, left posterior communicating arteries, right posterior communicating arteries, and basilar artery were significantly higher (TI >10 and arterial diameter >25%) than in the control. There was no significant difference in tortuosity index or artery diameter between the 15 and 25 mu groups for any of the 5 artery segments. CONCLUSION: Elastase injection through the cisterna magna can induce intracranial dolichoectasia in mice. Fifteen to 25 mu of elastase is an appropriate dose to use with acceptable mortality.