What is a dissecting fusiform aneurysm and how is it treated?

Dissecting Fusiform Aneurysm: Definition and Treatment

What is a Dissecting Fusiform Aneurysm?

A dissecting fusiform aneurysm is an abnormal focal dilation of a cerebral artery characterized by circumferential vessel wall involvement without a definable neck, often resulting from arterial wall dissection with intramural hematoma formation. 1

• Fusiform aneurysms lack the typical saccular shape and instead show diffuse, spindle-shaped arterial dilation involving the entire vessel circumference without separate inflow and outflow points 1
• Dissecting aneurysms occur when blood penetrates the arterial wall layers, creating intramural or intraluminal thrombosis, often with an intimal flap visible on imaging 1, 2
• These lesions arise from traumatic, infectious, or congenital causes in children, while atherosclerosis is the predominant cause in adults 1
• MRI findings distinguish dissecting from fusiform aneurysms: dissecting aneurysms show intimal flaps, double lumens, intramural hematoma, or hematoma adjacent to the parent artery, while pure fusiform aneurysms show only signal-void dilation 2

How Dissecting Fusiform Aneurysms are Fixed

Medical Management (First-Line for Uncomplicated Cases)

Aggressive blood pressure and heart rate control forms the foundation of treatment for uncomplicated dissecting fusiform aneurysms, particularly in the posterior circulation. 3

• Target systolic blood pressure 100-120 mmHg and heart rate ≤60 beats per minute to reduce shear stress on the arterial wall 3
• Administer intravenous beta-blockers as first-line therapy (propranolol, esmolol, or labetalol) 3
• Add vasodilators like sodium nitroprusside only after beta-blockade is established—never use vasodilators alone as they cause reflex tachycardia and increase aortic wall stress 3
• Transition to oral beta-blockers after 24 hours of hemodynamic stability, targeting long-term blood pressure <135/80 mmHg 3

Surgical Treatment Indications

Surgical or endovascular intervention is required for symptomatic aneurysms, those showing growth, or when complications develop including persistent pain, rapid expansion, rupture, or ischemic symptoms. 1

Microsurgical Options:

• Parent vessel occlusion (trapping) with or without bypass is the most definitive treatment when the vessel can be sacrificed 4, 5
• Bypass procedures are necessary when the aneurysm involves arteries supplying critical brain tissue:
  • Extra-intracranial bypass from superficial temporal artery to distal branches 5
  • End-to-side reanastomosis after aneurysm trapping to preserve perforators 4
  • High or low flow bypass depending on vascular territory at risk 5
• Wada testing should be performed preoperatively to identify vascular territories with greatest risk of neurological deficit and determine revascularization necessity 5
• Use cerebral protectors and mild hypothermia during microsurgical procedures 5

Endovascular Options:

• Flow diversion has emerged as the primary endovascular treatment, covering the entry tear and redirecting blood flow to promote thrombosis and healing 3, 6
• Stent-assisted coiling may be attempted in select cases, though the lack of a true neck makes this challenging 6
• Balloon fenestration can treat dynamic obstruction of branch arteries 1
• Endovascular treatment should be followed by DSA at 6 months, then annual MRA 1

Location-Specific Considerations

Posterior circulation dissecting fusiform aneurysms carry particularly high surgical risk and require more frequent monitoring than anterior circulation lesions. 1

• Vertebrobasilar aneurysms are intimately associated with brainstem perforators, increasing surgical complexity 1
• More frequent follow-up is mandatory for fusiform and dissecting aneurysms compared to saccular aneurysms 1
• Unruptured posterior circulation dissecting/fusiform aneurysms have considerable rupture rates during follow-up, with growth associated with morbidity even without rupture 7

Follow-Up Protocol

Lifelong surveillance with decreasing frequency is essential, as these aneurysms can undergo delayed recurrence through recanalization after thrombosis. 1

• Initial follow-up: MRA or DSA at 6 months 1
• Subsequent imaging: MRA at 1,2, and 5 years, then every 5 years for life 1
• Use non-contrast-enhanced MRA for long-term follow-up to avoid gadolinium accumulation 1
• DSA is preferred over MRA for initial post-treatment assessment at 6 months for endovascularly treated aneurysms 1
• Monitor for de novo aneurysm formation, particularly in patients with underlying vasculopathy 1

High-Risk Features Requiring Aggressive Treatment

Aneurysms with the following characteristics are classified as "complex" and warrant closer surveillance or prophylactic treatment: 1

• Giant size (>25 mm) 1
• Presence of daughter sacs 1
• Fusiform/dissecting/non-saccular morphology 1
• Arteries supplying normal brain arising from the aneurysm dome or neck 1
• Initial symptomatic presentation, diabetes, coronary disease, or large baseline diameter—all associated with growth and rupture risk 7

Common Pitfalls

• Never use vasodilators without prior beta-blockade as this increases wall stress through reflex tachycardia 3
• Avoid dihydropyridine calcium channel blockers without beta-blockers for the same reason 3
• Repeated angiography is essential when angiospasm makes differentiation between dissecting and fusiform aneurysms difficult 2
• Thrombosis can induce accelerated fibrinolysis leading to recanalization, necessitating vigilant lifelong follow-up 1
• Infectious dissecting aneurysms require frequent imaging to assess antibiotic effectiveness and detect early recurrence 1