▁is ▁a ▁type ▁of ▁is chem ic ▁stroke ▁with ▁an ▁unknown ▁origin , ▁defined ▁as ▁a ▁non - lac un ar ▁brain ▁inf arct ▁without ▁proxim al ▁ar ter ial ▁st en osis ▁or ▁card io emb ol ic ▁sources . ▁As ▁such , ▁it ▁forms ▁a ▁subset ▁of ▁crypt ogen ic ▁stroke , ▁which ▁is ▁part ▁of ▁the ▁TO AST - class ification . ▁The ▁following ▁di agnostic ▁criteria ▁define ▁an ▁ES US : ▁▁ ▁St roke ▁detected ▁by ▁CT ▁or ▁M RI ▁that ▁is ▁not ▁lac un ar ▁ ▁No ▁major - ris k ▁card io emb ol ic ▁source ▁of ▁em bol ism ▁ ▁Abs ence ▁of ▁ext rac ran ial ▁or ▁int rac ran ial ▁a ther os cl eros is ▁causing ▁ 5 0 % ▁lum inal ▁st en osis ▁in ▁ar ter ies ▁supp lying ▁the ▁area ▁of ▁is cha emia ▁ ▁No ▁other ▁specific ▁cause ▁of ▁stroke ▁identified ▁( e . g ., ▁ar ter itis , ▁dis section , ▁mig raine / vas osp asm , ▁drug ▁mis use ) ▁ ▁C aus es ▁ ▁The ▁following ▁factors ▁are ▁suggested ▁as ▁path ogen esis ▁of ▁ES US : ▁▁ ▁Sub cl in ical ▁at rial ▁f ibr ill ation : ▁Det ect able ▁in ▁~ 2 . 7 - 3 0 % ▁of ▁ES US ▁patients , ▁depending ▁on ▁duration ▁and ▁mod ality ▁of ▁E CG ▁monitoring . ▁ ▁Pat ent ▁for amen ▁ov ale ▁( P FO ): ▁Deep ▁ve in ▁th rom b