The goal of this clinical trial is to learn if flow diverter (FD) offers advantages over conventional stent-assisted coiling in the treatment of middle cerebral artery (MCA) bifurcation aneurysms . It will also learn about the safety of flow diverter (FD) treatment. The main questions it aims to answer are:

Does flow diverter (FD) treatment improves the rate of complete aneurysm occlusion and patients' neurological function? Does flow diverter (FD) treatment loweres the probability of aneurysm recurrence and the occurrence of complications?

Researchers will compare FD to a conventional stent-assisted coiling to see if FD treatment works better to treat MCA bifurcation aneurysms.

Participants will:

Undergo stent-assisted coiling or flow diverter treatment Take pre-operative and pre-discharge head MRI scans, neurological function assessments, and cognitive function assessments Visit the clinic 1 year for checkups and tests

Inclusion Criteria:

1. Unruptured wide-necked middle cerebral artery bifurcation aneurysms definitively diagnosed by CTA or DSA;
2. Aneurysms requiring stent-assisted embolization with the necessity of preserving branch arteries;
3. Indication for either flow diversion device or conventional stent-assisted coiling;
4. Age between 18 and 70 years, inclusive;
5. The subject or their legally authorized representative has signed the written informed consent form.

Exclusion Criteria:

1. Concomitant significant organ dysfunction (e.g., severe cardiac, hepatic, or renal insufficiency), chronic inflammatory disease, or malignancy;
2. Pregnant or lactating women;
3. Presence of significant neurological deficit (mRS score > 2);
4. Presence of contraindications to flow diversion device or stent-assisted coiling (e.g., severe allergy to metallic material, contraindication to antiplatelet medication);
5. Other conditions deemed unsuitable for enrollment by the investigator.