Types of Cerebral Aneurysms and Their Treatment
Classification of Cerebral Aneurysms
Cerebral aneurysms are classified into two major morphological categories: saccular (berry) aneurysms and fusiform aneurysms, with additional rare subtypes including dissecting, mycotic, marantic, and blister aneurysms. 1, 2
Saccular (Berry) Aneurysms
- Most common type, accounting for the vast majority of intracranial aneurysms 1
- Can be further subdivided based on relationship to branch vessels:
Fusiform Aneurysms
Rare Aneurysm Types
- Dissecting aneurysms: Result from intimal tear with blood dissecting into vessel wall 1
- Mycotic (infectious) aneurysms: Caused by septic emboli, typically located distally and far from typical congenital aneurysm sites 1, 3
- Blister aneurysms: Small, fragile lesions with thin walls 1
- Marantic aneurysms: Associated with malignancy 1
Treatment Approach by Rupture Status
Ruptured Aneurysms (Aneurysmal Subarachnoid Hemorrhage)
For patients with ruptured saccular aneurysms amenable to both techniques, endovascular coiling is preferred over surgical clipping for good-grade anterior circulation aneurysms to improve functional outcomes at 1 year. 4
Immediate Management Priorities
- Secure the aneurysm within 24 hours when feasible to prevent catastrophic rebleeding, which occurs in 2.4-10.8% of unsecured aneurysms with 80% mortality 4
- Administer nimodipine 60 mg orally every 4 hours for 21 consecutive days starting within 96 hours of hemorrhage onset, regardless of Hunt-Hess grade, to reduce ischemic deficits 4, 5
- Control blood pressure with titratable agents to balance rebleeding risk against cerebral perfusion 4
Treatment Selection Algorithm
- For good-grade aSAH with anterior circulation aneurysms: Choose endovascular coiling over clipping 4
- For middle cerebral artery aneurysms: Microsurgical clipping demonstrates advantage with current technology 6
- For basilar apex and vertebrobasilar confluence aneurysms: Endovascular repair shows advantage 6
- Treatment must be performed at high-volume centers (>35 cases/year) as low-volume hospitals (<10 cases/year) have inferior outcomes 4
Procedural Efficacy Data
- Surgical clipping rerupture rate: 0.1-0.3% annually after complete occlusion 6
- Endovascular coiling rerupture rate: 0.9% annually across all locations 6
- Degree of occlusion is the strongest predictor of rerupture: Complete occlusion carries 1.1% risk, 91-99% occlusion carries 2.9% risk, 70-90% occlusion carries 5.9% risk, and <70% occlusion carries 17.6% risk 7
Unruptured Intracranial Aneurysms (UIAs)
Treatment decisions for unruptured aneurysms must weigh size, location, patient age, and rupture risk against procedural morbidity, with observation being reasonable for small (<5mm) asymptomatic aneurysms in older patients. 6
Size-Based Treatment Algorithm
Aneurysms <5mm:
- Manage conservatively in virtually all cases 6
- Observation is reasonable, particularly in patients >65 years with low rupture risk 6
Aneurysms 5-10mm:
- Seriously consider treatment in patients <60 years of age 6
- In patients >65 years with medical comorbidities, observation is reasonable 6
Aneurysms >10mm:
- Treat in nearly all patients <70 years of age 6
- Large aneurysms carry approximately 1% annual rupture risk for 7-10mm lesions 6
Symptomatic Unruptured Aneurysms
With rare exceptions, all symptomatic unruptured aneurysms should be treated regardless of size, as symptoms indicate mass effect or hemodynamic compromise 6, 8
Treatment Modality Selection
Microsurgical clipping advantages:
- More durable protection against aneurysm regrowth and recurrence 6
- Preferred for middle cerebral artery aneurysms 6
- Should be first treatment choice in low-risk cases 6
Endovascular coiling advantages:
- Superior procedural morbidity/mortality profile (2.6% permanent complications vs 7-15% for surgery in patients >60 years) 6, 8
- Lower in-hospital mortality (0.4-0.5% vs 2.3-3.5% for surgery) 8
- Preferred for basilar apex and vertebrobasilar aneurysms 6
- Greater benefit in older patients (>60 years) as recurrence risk becomes less concerning over remaining lifespan 6
Emerging Technologies
- Flow-diverting stents and stent-assisted coiling may be considered in carefully selected cases 6
- Strict adherence to FDA indications is mandatory until long-term safety/efficacy data demonstrate superiority over existing technologies 6
- For ruptured saccular aneurysms amenable to coiling or clipping, stents or flow diverters should NOT be used due to higher complication risk 9
Special Aneurysm Types: Treatment Considerations
Mycotic (Infectious) Aneurysms
- Early targeted antimicrobial therapy is crucial and takes priority over aneurysm treatment 3
- Aneurysm elimination should be evaluated carefully as these lesions are typically fusiform, fragile, and located distally 3
- Blood cultures and evaluation for endocarditis are mandatory 3
- Reconstructive procedures often fail due to fragile aneurysm walls; parent vessel sacrifice may be necessary 3
Giant Aneurysms
In patients where both treatment and natural history carry high risks (such as giant aneurysms), nonoperative management is typically elected 6
Post-Treatment Management
Immediate Post-Procedure Assessment
- Obtain immediate cerebrovascular imaging after any repair to identify remnants or incomplete occlusion requiring retreatment 4, 9
- Document neurological examination within 24 hours to identify procedural complications 8
Long-Term Follow-Up
- Increase imaging frequency for incompletely obliterated aneurysms 6, 9
- Regular surveillance is necessary to detect recurrence and de novo aneurysm formation 6, 9
- Assessment of cognitive outcome in addition to standard measures is reasonable after any treatment 6, 9
Antiplatelet Therapy (for endovascular procedures)
- Dual antiplatelet therapy (aspirin 81-325mg plus clopidogrel 75mg daily) must be administered before and for minimum 30 days after endovascular procedures 8
Critical Pitfalls to Avoid
- Never use thrombolytics or anticoagulation in acute aSAH due to catastrophic rebleeding risk 4
- Do not treat at low-volume centers (<20 cases annually); transfer to high-volume centers is strongly indicated 6, 4
- Incomplete aneurysm occlusion dramatically increases rerupture risk; complete occlusion should be the goal whenever technically feasible 7
- Do not assume complete occlusion eliminates all risk; long-term follow-up imaging remains necessary 6, 9