Many unruptured cerebral aneurysms can be safely and durably treated with current microsurgical or endovascular techniques. The technical feasibility of aneurysm treatment is only one aspect of the comprehensive assessment for each patient. Part of the workup for a given patient is making a clinical decision on whether or not to treat the unruptured aneurysm. A host of factors including patient age, risk factors of aneurysm rupture, family history, and size/morphology of the aneurysm are considered. The anxiety seen in patients diagnosed with an unruptured cerebral aneurysm can be tremendous and this often drives the decision to treat in many cases. In this article we will review the epidemiology, pathophysiology, diagnostic workup, treatment strategies, and clinical outcomes that should be considered prior to making management decisions regarding unruptured cerebral aneurysms.
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• Saccular or “berry” aneurysms are abnormal focal outpouchings of cerebral arteries that typically occur at vessel bifurcations.
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• Unruptured intracranial aneurysms have an average prevalence of 2% to 3% in the general population.
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• Most cerebral aneurysms are acquired and occur spontaneously although traumatic, infectious, and malignancy-associated etiologies are also recognized.
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• Hypertension and cigarette smoking are significant modifiable risk factors associated with the occurrence of spontaneous cerebral aneurysms.
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• In general, cerebral aneurysms rupture at a rate of 1% to 2% per year depending on morphology and location.
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• Management options for patients with unruptured intracranial aneurysms include observation or treatment with either open surgery or endovascular techniques.
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• Treatment decisions for unruptured cerebral aneurysms should be made in consultation with an experienced, multidisciplinary neurovascular team.
Historical note and terminology
The modern era of unruptured cerebral aneurysm detection traces its roots to the development of cerebral angiography by Egas Moniz in the late 1920s (13). Prior to this time, unruptured cerebral aneurysms were primarily detected during autopsy or incidentally after craniotomy for a variety of indications. Initial treatment strategies for incidentally discovered unruptured cerebral aneurysms were often indirect with uncertain efficacy. Victor Horsley is credited with being the first surgeon to apply Hunterian ligation of the internal carotid artery for the treatment of an unruptured cerebral aneurysm in 1885 (33). Direct surgical obliteration of cerebral aneurysms would not occur until sometime later when Norman Dott successfully muscle wrapped a ruptured aneurysm in 1931 (45). Subsequently, Dott went on to pioneer the technique of aneurysm neck suture ligation. The era of cerebral aneurysm clip occlusion was ushered in by Walter Dandy, who in 1937 applied a silver clip to the neck of an unruptured posterior communicating artery aneurysm. Dandy reported an uneventful recovery with improvement in the patient’s preoperative third nerve palsy (11).
Diagnostic and therapeutic techniques for the management of unruptured cerebral aneurysms were further refined in the decades to come with the advent of microsurgery, improvement in catheter angiography and noninvasive imaging, and most recently, the development of endovascular occlusion methodologies. Much like initial open surgical strategies for the treatment of cerebral aneurysms, endovascular strategies were initially indirect, often utilizing proximal artery balloon occlusion. In the early 1990s, direct endovascular occlusion techniques were developed, culminating in FDA approval of platinum Guglielmi detachable coils in 1995 (16; 17).
Flow diverting stents such as the Pipeline embolization device (Medtronic), the SILK device (Balt), the surpass flow diverter (Stryker), the FRED flow redirection endoluminal device (Microvention), and others are now being investigated or routinely used to treat select anterior circulation aneurysms (08). The success seen with the use of these stents for select indications have led some to push the envelope in pursuing a variety of off-label uses to treat other complex aneurysms (32).
The latest tools in the armamentarium of the neurointerventionalist are intrasaccular devices that can be placed inside the aneurysm. Two such devices, the Woven EndoBridge (WEB) device (Microvention) and the Pulserider (Cerenovus) aneurysm neck reconstruction device, are the latest devices especially useful for wide neck aneurysms that would be challenging for coils and stents (38; 03).