Inclusion criteria

Inclusion criteria

• Patient with an intradural, saccular unruptured aneurysm in whom it is decided not to intervene with preventive endovascular or neurosurgical aneurysm repair and who are monitored on a regular basis for aneurysm growth
• 18 years or older
• Last aneurysm imaging with either CTA or MRA within the last 3 months
• Ability of subject to understand character and individual consequences of clinical trial
• Not legally incapacitated
• Written informed consent (must be available before enrolment in the trial
• For women with childbearing potential adequate contraception

Exclusion criteria

• All non-saccular UIAs or aneurysm related to arteriovenous malformations
• Daily ASA already prescribed for another indication
• Use of a vitamin K antagonist or direct oral anticoagulant (DOAC) at baseline
• History of hypersensitivity to ASA or to any other drug with similar chemical structure or to any excipient present in the pharmaceutical form of ASA
  
• History of asthma induced by ASA or other anti-inflammatory drugs
  
• Other contra-indications for low-dose ASA (81 mg - 100 mg per day) not yet mentioned, (e.g. bleeding disorders, gastric ulcers and/or intestinal ulcers, acute liver failure or kidney failure, severe heart failure, treatment with methotrexate in a dosage 15 mg/week or above)
  
• Use of another platelet aggregation inhibitor, which in combination with ASA would give an unacceptable risk of side effects/complications
• Chronic kidney disease stage IV and V (GFR < 30 mL/min/1.73 m2)
• Pregnancy and lactation
• Participation in another clinical trial or observation period of competing trials
• Life-expectancy <3 years