IntroductionConventional imaging of stroke was mainly dependent on computed tomography (CT), which included noncontrast imaging that assessed the ASPECTS (Alberta Stroke Program Early CT Score), contrast CT angiography, and CT perfusion. Though these techniques continue to be the mainstay in stroke imaging, there are certain disadvantages such as high radiation dose and need of contrast administration. Further, interpretation of the images can be difficult and, at times, impossible if the patient becomes noncooperative during the contrast study. Considering these issues, there is a need for an alternative imaging technique that gives the same information without contrast administration or radiation. Magnetic resonance imaging (MRI) sequences that include diffusion imaging, noncontrast perfusion arterial spin labeling (ASL) can probably have a distinct advantage. We present the successful use of ASL perfusion imaging in selecting patients for mechanical thrombectomy and the outcome. Keywords► arterial spin labeling ► perfusion imaging ► diffusion perfusion mismatch ► modified Rankin scale score AbstractPresence of ischemic penumbra is the principal factor that decides the need for mechanical thrombectomy in acute stroke patients with large vessel occlusion. Our objective was to evaluate the usefulness of arterial spin labeling (ASL) in detecting diffusion perfusion mismatch and directing patients into mechanical thrombectomy. We retrospectively studied all patients with acute nonhemorrhagic stroke in the anterior circulation, who had undergone stroke imaging with ASL followed by mechanical thrombectomy from July 2016 to November 2016. Area of diffusion perfusion mismatch was graded semiquantitatively into three grades: small, medium, and large. Mismatch was compared with 30-day modified Rankin scale (mRS) score. Interpretable PASL-perfusion images were obtained in all patients. Diffusion perfusion mismatches were present in all patients. Out of six patients with good mRS score, five patients had large diffusion perfusion mismatch. Two out of three patients with poor mRS were secondary to failed recanalization, in spite of large mismatch. One out of nine patients had poor outcome as well as a small area of mismatch. ASL is a rapid noninvasive imaging technique in acute stroke that has got the potential to detect ischemic penumbra.

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Paradoxical intracranial hemodynamic steal (IHS) is a contradictory reduction of cerebral blood flow volume in the territory of the impaired perfusion area occurring spontaneously or in response to vasodilatory stimuli, which can be recorded and evaluated on transcranial doppler (TCD). IHS followed by early neurological worsening (change in National Institute of Health Stroke Scale [NIHSS]> 2) in acute ischemic stroke patients has been described as reversed Robin Hood syndrome (RRHS). We describe two cases of RRHS following carotid artery stenting (CAS) in patients with contralateral carotid occlusion and its further management. Two patients with a history of anterior circulation strokes presented with recent complaints of dizziness and a sensation of being pulled back (patient 1), and episodic numbness of upper limbs (patient 2). On CT angiogram, both of the patients had severe extracranial internal carotid artery (ICA) stenosis on the symptomatic side associated with complete occlusion of the ICA on the contralateral side. In addition, both patients had impaired vasomotor reactivity (VMR) on TCD in the bilateral middle cerebral artery (MCA). Therefore, CAS on the symptomatic side was performed in both patients by femoral artery access without any periprocedural and postprocedural complications. However, on day 1 post CAS, complaints of transient upper limb tingling (patient 1) and limb shaking (patient 2) were reported corresponding to the completely occluded ICA, and TCD examinations confirmed RRHS in both patients. Patients were managed by decreasing the dose of antihypertensive medication to augment the blood pressure for 2 weeks. Normalization of the VMR on TCD was seen on follow-up, and both patients remain asymptomatic.