Vessel wall imaging in adult moyamoya disease with presumed acute in situ thrombotic occlusion: illustrative cases.

backgroundAlthough the hemodynamic mechanism of ischemic symptoms is widely accepted in moyamoya disease (MMD), acute thrombotic occlusion at a preexisting stenotic site may cause unexpected ischemic stroke. This phenomenon has rarely been addressed, particularly in relation to vessel wall MRI findings. OBSERVATIONS: Among 247 patients with MMD, 3 adults (1.2%, age range 33-59 years) exhibited radiological findings compatible with acute in situ thrombotic occlusion, defined as imaging-documented acute occlusion at a preexisting stenotic site and/or spontaneous recanalization on serial imaging. All 3 patients developed sudden-onset ischemic stroke despite relatively early angiographic stages and without preceding transient ischemic attacks. Two patients showed infarct patterns atypical for purely hemodynamic stroke, with basal ganglia involvement. Vessel wall MRI revealed marked contrast enhancement of the arterial wall at the site corresponding to the acute occlusion in all 3 patients. Neurological deficits remained after stroke in 2 patients, whereas the patient who had been receiving antiplatelet therapy had no residual deficits. LESSONS: These cases highlight presumed acute in situ thrombotic occlusion as a possible mechanism of ischemic stroke in adult MMD and suggest a potential role for vessel wall MRI in risk stratification and management. https://thejns.org/doi/10.3171/CASE26208.