Other determined etiologies of young stroke patients with middle cerebral artery (MCA) stenosis. a: A 50-year-old man with arterial dissection. A1: Acute ischemic stroke in left temporal lobe on diffusion weighted imaging (DWI). A2: Stenosis in M1 segment of left MCA by Magnetic resonance angiography (MRA) (arrows). A3, A4: T1 hyperintensities indicate intramural hematoma in M1 segment of left MCA by high resolution magnetic resonance imaging (HR-MRI) (arrows). b: A 54-year-old man with vasculitis. B1: Acute ischemic stroke in right temporal lobe, frontal lobe and basal ganglia on DWI. B2: Segmental stenosis of the right MCA on MRA (arrows). B3: Concentric thickening of vascular wall of the right MCA on HR-MRI T1 sequence. B4: Concentric wall enhancement on T1 post-contrast HR-MRI (arrows). c: A 54-year-old man with Moyamoya disease. C1: Acute ischemic stroke in right temporal lobe on DWI. C2: Ivy sign on sulcus surfaces on axial post contrast T1 sequence (circle). C3, C4: Steno-occlusive changes of the right internal carotid artery (ICA) and abnormal vascular networks (Moyamoya vessels) in digital substraction angiography (DSA) (arrows). d: A 29-year-old man with mitochondrial disease. D1: Acute lesion in right parietal lobe on DWI. D2: Ragged-red fibers (RRF) were observed on Gomori trichrome staining. D3: Genetic mutation: tRNA m.3234A>G. e: A 54-year-old women with patent foramen ovale (PFO). E1: Infarction in right parietal lobe with hyperintensities on fluid attenuated inversion recovery (FLAIR) (arrows). E2: PFO was found during the operation (arrows). E3: Microembolic signal was observed in transcranial doppler ultrasound.