Increased vessel diameter of leptomeningeal anastomoses after hypoxic preconditioning

Angiographic Pattern of M1 Stenosis Predicts Territorial Stroke in Patients Receiving Aggressive Medication without Stenting

OBJECTIVE

To evaluate the relationship between different angiographic patterns of middle cerebral artery M1 segment stenosis and related territorial stroke in patients receiving aggressive medical treatment without stenting.

METHODS

We retrospectively reviewed our patient registry database to identify ICAS patients diagnosed by digital subtraction angiography between January 2017 and December 2020 and identified 3 different angiographic patterns (normal, shift, and dilation) in 124 patients with M1 stenosis. The association between these patterns and recurrent ischemic stroke in the M1 territory was analyzed.

RESULTS

The rates of recurrent M1 territorial stroke and transient ischemic attack in the normal group, shift group, dilation group and shift-dilation group were 34.5%, 35.0%, 78.3%, and 44.4% respectively. In patients with the shift pattern, the rate of recurrent stroke is significantly higher at a deflection angle ≥9.32° than at a deflection angle <9.32°(P < 0.05). In patients with dilation pattern, the rate of recurrent stroke is significantly higher than patients with non-dilation pattern (72.3% vs. 36.8%, P < 0.05).

CONCLUSIONS

Angiographic patterns of M1 stenosis may predict recurrent territorial strokes, thus providing a surrogate marker to identify high-risk patients for potential endovascular treatment.

Immediate remote ischemic postconditioning reduces cerebral damage in ischemic stroke mice by enhancing leptomeningeal collateral circulation

Remote ischemic postconditioning (RIPC) is a promising neuroprotective strategy for ischemic stroke. Here, we employed a focal ischemic stroke mouse model to test the hypothesis that poststroke collateral circulation as a potent mechanism of action underlying the therapeutic effects of immediate RIPC. During reperfusion of cerebral ischemia, the mice were randomly assigned to receive RIPC, granulocyte colony‐stimulating factor (G‐CSF) as a positive control, or no treatment. At 24 hr, we found RIPC and G‐CSF increased monocytes/macrophages in the dorsal brain surface and in the spleen, coupled with enhanced leptomeningeal collateral flow compared with nontreatment group. Blood monocytes depletion by 5‐fluorouracil (5‐FU) significantly limited the neuroprotection of RIPC or G‐CSF treatment. The protein expression of proangiogenic factors such as Ang‐2 was increased by ischemia, but treatment with either RIPC or G‐CSF showed no further upregulation. Thus, immediate RIPC confers neuroprotection, in part, by enhancing leptomeningeal collateral circulation in a mouse model of ischemic stroke.

Stroke Mimics: The Quest for Leptomeningeal Anastomoses and Isolated Diffusion-Weigthed MR Signal

Stroke is caused by occlusion of a medium- or large-sized vessel in the brain. The treatment with either intravenous or intra-arterial thrombolysis is based on an accurate and time-sensitive diagnosis. On clinical and imaging grounds a number of entities-seizures, toxic-metabolic, infectious, or demyelinating diseases-can mimic stroke. Identifying them is paramount as the treatment differs significantly. Prior imaging reviews have focused on the nonterritorial distribution of these mimics. However, some important questions arise here. Are the vascular territories and their boundaries invariable in the human brain? Where should we draw the lines separating arterial territories? van der Zwan and colleagues addressed these questions decades ago. For him and others, the leptomeningeal anastomoses-a contentious concept for some but increasingly linked to collateral flow in stroke-is an important anatomic structure with significant variations in their distribution and pathophysiology. Variations in blood supply appear larger that traditionally taught. We revisit this concept and entertained their implications in cases of stroke mimics. For instance, the distribution of abnormalities in some toxic-metabolic processes appear to correlate with areas where rich leptomeningeal anastomoses are expected. We will also explore the concept of hyperintense signal on diffusion weighted-imaging with no correlated changes on apparent diffusion coefficient maps. We name this finding as "isolated DWI signal" and lay-out its importance in the recognition of many entities mimicking stroke. Taking together, the discussed anatomic and imaging concepts will help radiologists and clinicians to recognize not only the common but the unusual entities imitating stroke in the emergency room.

Computer modeling of anterior circulation stroke: proof of concept in cerebrovascular occlusion

BACKGROUND

Current literature emphasizes the role of the Circle of Willis (CoW) in salvaging ischemic brain tissue but not that of leptomeningeal anastomoses (LA). We developed a computational model of the cerebral circulation to (1) evaluate the roles of the CoW and LA in restoring flow to the superficial compartment of the middle cerebral artery (MCA) territory and (2) estimate the size of the LA required to maintain flow above the critical ischemic threshold (>30% of baseline) under simulated occlusion.

METHODS

Cerebral vasculature was modeled as a network of junctions connected by cylindrical pipes. The experiments included occlusion of successive distal branches of the intracranial arteries while the diameters of LA were varied.

RESULTS

The model showed that the region of reduced flow became progressively smaller as the site of occlusion was moved from the large proximal to the smaller distal arteries. There was no improvement in flow in the MCA territory when the diameters of the inter-territorial LA were varied from 0.0625 to 0.5 mm while keeping the intra-territorial LA constant. By contrast, the diameter of the inter-territorial LA needed to be >1.0 mm in order to provide adequate (>30%) flow to selected arteries in the occluded MCA territory.

CONCLUSION

The CoW and inter-territorial LA together play important supportive roles in intracranial artery occlusion. Computational modeling provides the ability to experimentally investigate the effect of arterial occlusion on CoW and LA function.

Cerebral hemodynamic and metabolic effects of remote ischemic preconditioning in patients with subarachnoid hemorrhage

BACKGROUND

Remote ischemic preconditioning (RIPC) is a form of endogenous neuroprotection induced by transient, subcritical ischemia in a distant tissue. RIPC effects on cerebral hemodynamics and metabolism have not been explored in humans. This study evaluates hemodynamic and metabolic changes induced by RIPC in patients with aneurysmal subarachnoid hemorrhage (SAH).

METHODS

Patients underwent three or four RIPC sessions 2-12 days following SAH. Continuous vitals, intracranial pressure (ICP), and transcranial Doppler (TCD) data were collected. Brain microdialysis metabolic changes were monitored. ICP and TCD morphological clustering and analysis of intracranial pulse (MOCAIP) metrics were compared to positive and negative control groups for cerebral vasodilation.

RESULTS

Seven ICP and six TCD recordings from four patients demonstrated an increase in mean ICP (8-14.57 mmHg, p < 0.05). There was a reduction in middle cerebral artery (MCA) mean velocities (111-87 cm/s, p = 0.039). ICP and TCD MOCAIP metrics demonstrated variances consistent with vasodilation that returned to baseline following the RIPC. Over the duration of the RIPC, microdialysis showed reduction in the lactate/pyruvate (L/P) ratio (42.37-33.77, p = 0.005) and glycerol (174.04-126 μg/l, p < 0.005), which persisted for 25-54 h after the last RIPC.

CONCLUSIONS

This study demonstrated cerebrovascular effects induced by RIPC consistent with transient vasodilation. Cerebral metabolic effects suggest protection from ischemia and cell membrane preservation lasting up to 2 days following RIPC.

Identifying the inertial cavitation threshold and skull effects in a vessel phantom using focused ultrasound and microbubbles

Focused ultrasound (FUS) in combination with microbubbles has been shown capable of delivering large molecules to the brain parenchyma through opening of the blood-brain barrier (BBB). However, the mechanism behind the opening remains unknown. To investigate the pressure threshold for inertial cavitation of preformed microbubbles during sonication, passive cavitation detection in conjunction with B-mode imaging was used. A cerebral vessel was simulated by generating a cylindrical hole of 610 microm in diameter inside a polyacrylamide gel and saturating its volume with microbubbles. Definity microbubbles (Mean diameter range: 1.1-3.3 microm, Lantheus Medical Imaging, N. Billerica, MA, USA) were injected prior to sonication (frequency: 1.525 MHz; pulse length: 100 cycles; PRF: 10 Hz; sonication duration: 2 s) through an excised mouse skull. The acoustic emissions due to the cavitation response were passively detected using a cylindrically focused hydrophone, confocal with the FUS transducer and a linear-array transducer with the field of view perpendicular to the FUS beam. The broadband spectral response acquired at the passive cavitation detector (PCD) and the B-mode images identified the occurrence and location of the inertial cavitation, respectively. Findings indicated that the peak-rarefactional pressure threshold was approximately equal to 0.45 MPa, with or without the skull present. Mouse skulls did not affect the threshold of inertial cavitation but resulted in a lower inertial cavitation dose. The broadband response could be captured through the murine skull, so the same PCD set-up can be used in future in vivo applications.

Granulocyte-Macrophage Colony-Stimulating Factor–Induced Vessel Growth Restores Cerebral Blood Supply After Bilateral Carotid Artery Occlusion

BACKGROUND AND PURPOSE

Hemodynamic compromise due to occlusive cerebrovascular disease is associated with an increased stroke risk. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been suggested to stimulate collateral blood vessel growth in various models of hemodynamic compromise. The purpose of this study was to investigate the effects of GM-CSF on cerebral hemodynamics and vessel growth in a rat model of chronically impaired cerebral blood flow (CBF).

METHODS

Male Sprague-Dawley rats underwent sequential bilateral carotid artery occlusion (BCO) and were treated with GM-CSF or saline for 6 weeks. Sham-occluded animals served as a control group. Baseline CBF was measured by iodo[(14)C]antipyrine autoradiography, and cerebrovascular reserve capacity was assessed by laser-Doppler flowmetry after application of 20 mg/kg body weight acetazolamide. The capillary density and arterioles immunopositive for alpha-smooth muscle actin were counted on brain sections. The cerebral angioarchitecture was visualized with a latex perfusion technique.

RESULTS

Baseline CBF as measured by iodo[(14)C]antipyrine autoradiography was not affected by BCO. The cerebrovascular reserve capacity, however, was significantly impaired 1 week after BCO. CBF and cerebrovascular reserve capacity recovered completely in GM-CSF-treated animals but not in solvent-treated animals. Histologic analysis of the hippocampus revealed integrity of the hypoxia-vulnerable neurons in all animals. The capillary density showed a very mild increase in GM-CSF-treated animals. However, the number of intraparenchymal and leptomeningeal arterioles was significantly higher in GM-CSF-treated animals than in both other groups.

CONCLUSIONS

Long-term GM-CSF treatment in a BCO model in rats leads to restoration of impaired cerebral hemodynamics and accompanies structural changes in the resistance-vessel network.