48-year-old Asian woman presented to the emergency department after two weeks of gradually worsening left leg weakness & numbness. She was diagnosed with subacute right MCA-ACA border-zone infarct on clinical assessment and MRI. Vessel imaging with CTA suggested widespread obstructive arteriopathy involving bilateral ACA and MCA while sparing the terminal ICA and posterior circulation, with extensive collateral development in lenticulostriate vasculature. Cerebral angiogram confirmed the CTA findings with no signs of diffuse atherosclerosis or inflammation, raising concern for Moyamoya syndrome despite the lack of ICA termini involvement. 

To rule out inflammatory etiology of arteriopathy, she underwent a diagnostic LP, and 24cc of clear fluid was collected, which was non-inflammatory. Towards the end of the procedure, she developed global aphasia, left-sided gaze deviation, right-sided hemiplegia & homonymous hemianopsia, suggestive of left MCA syndrome, while being normotensive and in a supine position. CT perfusion map showed 131 mL of left MCA/ACA territory penumbra with no core infarct. She was placed in Trendelenburg position and resuscitated with fluids and phenylephrine to maintain high MAP goal. This was followed by rapid resolution of her left MCA syndrome within one hour.