What are the criteria for selecting an intracranial aneurysm for endovascular coiling?

Criteria for Brain Aneurysm Coiling

Endovascular coiling is appropriate for intracranial aneurysms based on specific anatomic characteristics, patient factors, and clinical presentation, with the strongest indication being ruptured aneurysms in the posterior circulation or those with favorable neck geometry (narrow neck <5mm, dome-to-neck ratio <0.5). 1

Anatomic Selection Criteria

Aneurysm Location (Primary Determinant)

• Posterior circulation aneurysms (basilar, vertebrobasilar, posterior cerebral arteries) are preferentially treated with coiling over surgery, as comparative studies demonstrate better outcomes with endovascular approach in these locations 1
• Cavernous segment internal carotid artery aneurysms are ideal for coiling, as they are surgically difficult to access but relatively easily treated endovascularly 1
• Paraclinoid/ophthalmic artery aneurysms favor endovascular treatment due to their deep location making surgical access technically challenging 2
• Middle cerebral artery aneurysms are frequently difficult to treat by coiling and surgical results are often more favorable, making these less ideal candidates 1

Neck Geometry (Critical Technical Factor)

• Narrow neck diameter <5 mm is associated with better outcomes in terms of both complication rates and likelihood of complete occlusion 1
• Dome-to-neck ratio <0.5 predicts higher success rates for complete occlusion by coil embolization 1
• Wide-necked aneurysms (>4mm) not amenable to primary coiling can be treated with stent-assisted coiling or flow diverters (Class IIa recommendation) 3, 2

Aneurysm Size Considerations

• Optimal size range: Aneurysms between 3-25mm are most suitable for coiling 1
• Very small aneurysms (<3mm) are technically difficult to coil and carry higher intraoperative rupture risk 1
• Giant aneurysms (>25mm) have increased complication risk and decreased likelihood of complete occlusion, though coiling still shows better outcomes than surgery for these lesions 1

Clinical Presentation Criteria

Ruptured Aneurysms (Class I Indication)

• Endovascular coiling is the preferred treatment for ruptured aneurysms deemed technically suitable for both coiling and clipping (Class I, Level B evidence), as it provides 7% absolute reduction in unfavorable outcomes at 1 year 1, 3, 2
• Treatment should be performed within 24-72 hours to reduce the 20-30% rebleeding risk in the first month 3
• Poor Hunt-Hess grade or brain swelling without mass lesion favors coiling, as these conditions increase surgical retraction risk but have less influence on coiling difficulty 1
• Large parenchymal hematoma with mass effect (>50mL) favors surgical clipping for simultaneous hematoma evacuation and aneurysm securing, reducing mortality from 80% to 27% 3

Unruptured Aneurysms

• Posterior communicating artery location carries higher rupture risk than other anterior circulation sites, warranting treatment in patients under 60 years with aneurysms >5mm 3
• Aneurysms >7mm in anterior circulation have 0.1% annual rupture risk, increasing with size 1
• Posterior circulation aneurysms have 2.5-50% rupture risk depending on size, making treatment threshold lower 1

Patient-Specific Factors

Age Considerations

• Patients over 65 years with ruptured aneurysms may benefit more from coiling based on outcomes data 3
• Patients under 40 years should be considered for surgical clipping when feasible, as clipping offers "at least an order of magnitude more durable" protection with 99.4% long-term occlusion rates 3, 2
• Patients 60-70 years with unruptured posterior communicating artery aneurysms should be offered treatment given higher rupture risk and low treatment morbidity 3

Medical Comorbidities

• Contraindications to radiographic contrast (known allergy, renal failure) preclude endovascular approach 1
• Significant medical comorbidities that increase surgical risk favor endovascular treatment 1
• Inability to tolerate dual antiplatelet therapy is a relative contraindication to stent-assisted coiling 3, 4

Technical Feasibility Requirements

Procedural Considerations

• Both neurosurgical and endovascular specialists must evaluate the aneurysm together to determine optimal treatment strategy (Class I, Level C evidence) 3
• Coiling achieves complete occlusion in approximately 79% of cases initially, with 88% achieving >90% occlusion 2
• Recanalization occurs in 12% of cases, with retreatment needed in 6.4% 4
• Aneurysms with incorporated arteries require specialized coiling techniques to avoid branch occlusion 5

Critical Contraindications to Coiling in Acute Setting

• Avoid stents or flow diverters in acute ruptured saccular aneurysms when primary coiling or clipping is feasible (Class III: Harm, Level B-NR), as dual antiplatelet therapy requirements increase hemorrhagic complications, particularly ventriculostomy-related bleeding 3

Common Pitfalls to Avoid

• Do not assume elderly patients (>70 years) automatically benefit from coiling - randomized data shows no clear benefit over clipping in this age group; base decisions on aneurysm characteristics 3
• Incomplete occlusion increases rebleeding risk - complete obliteration should be the goal whenever possible (Class I, Level B evidence) 3
• Previously coiled aneurysms, larger size, and incomplete initial occlusion predict higher recanalization rates requiring surveillance 4
• Symptomatic unruptured aneurysms (presenting with cerebral ischemia or mass effect) carry greater treatment risk than truly incidental aneurysms 3

Follow-Up Requirements

• Delayed follow-up vascular imaging is mandatory after coiling (Class I, Level B evidence), with timing individualized based on completeness of initial treatment 3
• Catheter angiography remains the preferred follow-up modality despite <0.1% permanent complication risk 1, 3
• Retreatment should be strongly considered for clinically significant or growing remnants 3
• Plain skull x-rays may identify coil compaction indicating aneurysm recanalization 1