In monitoring of recanalization and in sonothrombolysis, contrast-enhanced ultrasound (CEUS) is applied in extended time protocols. As extended use may increase the probability of unwanted effects, careful safety evaluation is required. We investigated the safety profile and beneficial effects of CEUS in a reperfusion model. Wistar rats were subjected to filament occlusion of the right middle cerebral artery (MCA). Reperfusion was established after 90 minutes, followed by recombinant tissue-type plasminogen activator (rt-PA) treatment and randomization to additional CEUS (contrast agent: SonoVue; 60 minutes). Blinded outcome evaluation consisted of magnetic resonance imaging (MRI), neurologic assessment, and histology and, in separate experiments, quantitative 3D nano-computed tomography (CT) angiography (900 nm 3 voxel size). Nano-CT revealed severely compromised microcirculation in untreated animals after MCA reperfusion. The rt-PA partially improved hemispheric perfusion. Impairment was completely reversed in animals receiving rt-PA and CEUS. This combination was more effective than treatment with either CEUS without rt-PA or rt-PA and ultrasound or ultrasound alone. In MRI experiments, CEUS and rt-PA treatment resulted in a significantly reduced ischemic lesion volume and edema formation. No unwanted effects were detected on MRI, histology, and intracranial temperature assessment. This study shows that CEUS and rt-PA is safe in the situation of reperfusion and displays beneficial effects on the level of the microvasculature.

Ischemic stroke causes cell necrosis with the exposure of extracellular ribonucleic acid (RNA) and other intracellular material. As shown recently, extracellular RNA impaired the blood-brain-barrier and contributed to vasogenic edema-formation. Application of ribonuclease 1 (RNase 1) diminished edema-formation and also reduced lesion volume in experimental stroke. Here we investigate whether reduction of lesion volume is due to the reduction of edema or of other neuroprotective means. Neuroprotective and edema protective effects of RNase 1 pretreatment were assessed using a temporary middle cerebral artery occlusion (MCAO) model in rats. Lesion volume was assessed on magnetic resonance imaging (MRI). T2-relaxation-time and midline-shift as well as brain water content (wet-dry-method) were measured to quantify edema formation. The impact of edema formation on infarct volume was evaluated in craniectomized animals. Exogenous RNase 1 was well tolerated and reduced edema-formation and infarct size (26.7% +/- 10.7% vs. 41.0% +/- 10.3%; p<0.01) at an optimal dose of 42 microg/kg as compared to placebo. Craniectomized animals displayed a comparable edema reduction but no reduction in infarct size. The present study introduces a hitherto unrecognized mechanism of ischemic brain damage and a novel neuroprotective approach towards acute stroke treatment.

The data indicated that collateral damage caused by the space-occupying effect of a large MCA territory stroke contributes seriously to ischemic lesion formation. The elimination of increased ICP thus must be regarded as a highly neuroprotective measure, rather than only a life-saving procedure to prevent cerebral herniation. Further clinical trials should reveal the neuroprotective potential of surgical and pharmacological ICP-lowering therapeutic approaches.

Vasogenic brain edema occurs much earlier than expected following permanent MCAO and leads to MLS and mechanical compression of adjacent brain structures. Since compression effects can impair rCBF, early edema formation can significantly contribute to infarct formation and thus represents a promising target for neuroprotection.