How are narrow‑neck and wide‑neck intracranial aneurysms defined by neck width and dome‑to‑neck ratio, and how do these measurements influence the choice of endovascular treatment (coiling, balloon remodeling, stent‑assisted coiling, or flow‑diversion) and the need for antiplatelet therapy?

Defining Narrow-Neck versus Wide-Neck Intracranial Aneurysms

By established convention, a narrow-neck aneurysm has a neck diameter ≤4 mm, while a wide-neck aneurysm has a neck diameter >4 mm or a dome-to-neck ratio <2:1. 1, 2

Standard Measurement Definitions

Neck Width Classification

• Narrow neck: Maximum neck width ≤4 mm 1
• Wide neck: Maximum neck width >4 mm 1, 2

Dome-to-Neck Ratio

• Favorable geometry for simple coiling: Dome-to-neck ratio ≥2:1 1, 2
• Wide-neck classification: Dome-to-neck ratio <2:1 1, 2
• Combined definition (most commonly used): Neck ≥4 mm OR dome-to-neck ratio <2 is the most prevalent definition in the literature, appearing in 39.8% of published studies 3

Parent Artery-to-Neck Ratio

• The relationship between parent artery diameter and aneurysm neck size is critical for treatment planning 1, 2
• A 4-mm aneurysm neck relative to a 2-mm parent artery diameter argues for adjunctive devices even if the dome-to-neck ratio appears favorable 1

Impact on Endovascular Treatment Selection

Narrow-Neck Aneurysms (≤4 mm, dome-to-neck ≥2:1)

• Primary coiling without adjunctive devices is appropriate when geometry is favorable 1, 2
• Stand-alone coiling was used in only 9.3% of wide-neck cases versus being standard for narrow-neck aneurysms 4
• No antiplatelet therapy required for simple coiling 2

Wide-Neck Aneurysms (>4 mm OR dome-to-neck <2:1)

Treatment algorithm based on morphology:

Balloon Remodeling Technique

• Temporary balloon inflation across the aneurysm neck during coil deployment 2
• Balloon is deflated and removed after coiling is complete 2
• Particularly useful when parent vessel preservation is critical 2
• Used in 17.1% of wide-neck cases 4
• Does not require long-term antiplatelet therapy since the balloon is removed 2

Stent-Assisted Coiling

• Self-expandable stent deployed across the aneurysm neck creates a scaffold preventing coil herniation 2
• Used in 34.3% of wide-neck cases 4
• Requires dual antiplatelet therapy (DAPT), which increases hemorrhagic risk especially in ruptured aneurysms 2
• The Neuroform stent series has demonstrated safe navigation and increased aneurysm neck coverage for wide-necked lesions 5

Flow-Diverting Stents

• Low-porosity stents redirect flow away from the aneurysm while providing scaffold for endothelial growth 2
• Used in 37.1% of wide-neck cases 4
• May represent a better option for many saccular wide-neck aneurysms 2
• Requires dual antiplatelet therapy with associated hemorrhagic risks 2

Critical Measurement Considerations

Imaging Requirements

• Catheter cerebral arteriography provides the highest spatial resolution for evaluating dome-to-neck ratio, neck-to-artery ratio, and exact aneurysm dimensions 1
• Optimal orthogonal arteriographic projections or rotational angiography with 3D reconstructions are essential 1, 2
• Digital subtraction angiography was the only imaging modality used in 71.3% of studies defining wide-neck aneurysms 3

Measurement Pitfalls

• There is inconsistent reporting in the literature regarding which precise dome measurements should be used to determine the dome-to-neck ratio 3
• Multilobulated or complex shapes create difficulty in volume analysis and should be described separately 1
• Some aneurysms have no definable neck with separate inflow and outflow, making standard definitions inapplicable 1

Antiplatelet Therapy Requirements

No Antiplatelet Therapy Needed

• Simple coiling of narrow-neck aneurysms 2
• Balloon remodeling technique (balloon is removed after procedure) 2

Dual Antiplatelet Therapy Required

• Stent-assisted coiling 2
• Flow-diverting stents 2
• Major caveat: DAPT increases hemorrhagic risk, particularly problematic in subarachnoid hemorrhage settings 2

Treatment Outcomes and Follow-Up

Angiographic Outcomes

• Complete aneurysm obliteration should be the goal whenever possible to reduce rebleeding risk 2
• Adequate angiographic occlusion (Raymond scale 1-2) was achieved in 86.5% of endovascular cases versus 97.6% of microsurgical cases for wide-neck aneurysms 4
• Complete aneurysm occlusion is less likely in larger aneurysms with wide necks 2

Recurrence and Retreatment

• Aneurysm recurrence is not uncommon after endovascular coiling, even in initially completely occluded aneurysms 2
• Additional embolizations are often required during follow-up for wide-neck aneurysms 2
• Long-term angiographic monitoring is mandatory, with follow-up imaging at 6 months and then annually 2
• One patient in a series required further coil embolization based on 6-month follow-up findings 5

Clinical Outcomes

• Wide-neck status was associated with worse clinical outcomes at all time points compared to narrow-neck aneurysms 6
• Neurological morbidity from procedural complications was lower with endovascular therapy (1.4%) versus microsurgery (10.3%) for wide-neck aneurysms 4
• Good clinical outcome at 1 year was achieved in 93.4% of endovascular cases versus 84.1% of microsurgical cases 4