Aspirin Treatment for Small Unruptured InTracranial Aneurysms With Ischemic cereBrovascuLar diseasE

Inclusion Criteria: * patients aged more than 18 and less than 80 years * patients with UIAs \< 5 and ≥2 mm in the greatest diameter confirmed by MR angiography (MRA), computed tomography angiography (CTA) , or digital subtraction angiography (DSA) * patients with either symptomatic ICVD (ischemic stroke or transient ischemic attack) or asymptomatic ICVD (clinically silent lacunar infarction identified on brain CT/MR imaging) * last aneurysm imaging with either CTA or MRA or DSA within the last 3 months * ability of the subject to understand character and individual consequences of clinical trial * patients who provided written informed consent * patients who consented to follow-up imaging with the same MR angiography or CT angiography modality Exclusion Criteria: * multiple aneurysms * a history of intracranial aneurysm rupture-related hemorrhage * a family history of intracranial aneurysm * a history of vascular malformation (brain arteriovenous malformation, moyamoya disease, arteriovenous fistula, etc.), brain tumor, hydrocephalus, or hypertensive cerebral hemorrhage etc. * MR contraindications (metallic implant, contrast medium allergy, claustrophobia, etc). * a precondition modified Rankin Scale (mRS) score \> 2 * fusiform or daughter sac UIAs * an allergy to aspirin * other contraindications for aspirin not yet mentioned, in the dosage of 100 mg/day (e.g. bleeding disorders, gastric or intestinal ulcers, acute liver failure or kidney failure, severe heart failure, treatment with methotrexate in a dosage 15 mg/week or above) * pregnancy and lactation * participation in another clinical trial or observation period of competing trials * residence in a rural area that prevented regular follow-up * poor compliance