35 Previously Coiled Recurrent Aneurysms of the Anterior Circulation
Abstract
Multiple large randomized clinical trials have led to the widespread adoption of endovascular treatment of cerebral aneurysms. Cerebrovascular neurosurgeons are therefore increasingly confronted with recurrent or residual aneurysms that have been previously treated with endovascular coiling. Previously treated aneurysms present unique anatomical and decision-making challenges to open microsurgical or endovascular retreatment. In this chapter, we discuss several major controversies complicating clinical decision making when treating previously coiled cerebral aneurysms. Topics addressed include whether treatment is indicated, selection of treatment modality (microsurgical vs. endovascular), anatomical considerations that should guide selection of the optimal microsurgical technique (clipping vs. bypass), and complication avoidance.
Introduction
Multiple large randomized clinical trials—the International Subarachnoid Aneurysm Trial (ISAT) and Barrow Ruptured Aneurysm Trial (BRAT)—have led to the widespread adoption of endovascular treatment of cerebral aneurysms. However, many of these techniques are associated with lower rates of complete aneurysm occlusion than microsurgical clipping. Incomplete obliteration and/or compaction of the coil mass may lead to aneurysm recurrence over time. In the reported literature, rates of residual and recurrent aneurysms range from 39 to 61% and 13 to 21%, respectively.
Cerebrovascular neurosurgeons are increasingly confronted with recurrent or residual aneurysms previously treated with endovascular coiling. At the University of California San Francisco, there was in excess of a threefold increase in the number of incompletely coiled and recurrent aneurysms requiring microsurgical treatment from 1997 to 2007. More recent publication has suggested that the incidence of retreatment has stabilized. Still, retreatment following endovascular coiling represents approximately 2% of all microsurgically treated aneurysms and is most commonly encountered for aneurysms in the anterior circulation.
Major controversies in decision making addressed in this chapter include:
Whether or not treatment is indicated.
Microsurgical versus endovascular treatment of previously coiled anterior circulation aneurysms.
Anatomical guidance of proper selection of microsurgical technique.
Whether to Treat
There is an absence of unequivocal clinical evidence to guide decision making for retreatment of recurrent aneurysms after endovascular coiling. This leads to substantial variability among experienced clinicians on whether to re-treat. The decision to re-treat and selection of appropriate technique requires careful clinical judgment on a case-by-case basis (▶ Fig. 35.1 ). Risk of rehemorrhage from residual and/or recurrent aneurysms following endovascular coiling is not trivial. Published studies—including ISAT, BRAT, and Cerebral Aneurysm Rerupture Treatment (CARAT)—have suggested that the annual risk for rebleeding after coiling ranges from 0 to 1.3%, but varies with the timing from initial intervention. For example, in CARAT and ISAT, rates of rerupture in the first year following treatment occur in 1.7 and 1.8%, respectively, across treatment modalities, but may be as high as 3.4% in those treated with endovascular coiling. After the first year, the annual risk declines, but remains higher in those treated with endovascular coiling (endovascular: 1.56 per 1,000 patient-years; microsurgical clipping: 0.49 per 1,000 patient-years). Despite this relative infrequency, rerupture of previously treated aneurysms is frequently neurologically devastating with a mortality rate up to 58% ( 1 , 2 in algorithm ).
The identification of clues of looming rupture in the context of previously coiled aneurysms is less well established. Similar to the initial treatment of cerebral aneurysms, factors to consider are size, location, and morphology of the recurrent aneurysm and whether it previously ruptured. Additional factors unique to recurrence should also be considered, including time since initial treatment and degree of aneurysmal occlusion. In the CARAT study, the risk of rerupture of recurrent aneurysms varied as a function of initial aneurysm occlusion (overall risk: 1.1% for complete occlusion, 2.9% for 91–99% occlusion, 5.9% for 70–90%, and 17.6% for <70% occlusion). Given the consequences of rerupture, we favor retreatment when postcoiling residual or recurrence is detected in our center. However, desires to treat should be tempered by the patient′s perioperative risk including age and comorbid conditions, patient preference, surgeon or interventionist experience, and likelihood of successful intervention, and clinicians should engage in detailed risk versus benefit discussions with the patient and/or family to carefully design the most appropriate treatment plan.
Anatomical Considerations
Recurrence following endovascular coiling presents challenging anatomy not present in an untreated aneurysm. The normal soft, compressible sac is no longer empty, but now filled with a hard coil mass that prevents collapse or softening of the aneurysmal dome with application of temporary clips. Coil-induced separation between the aneurysm′s walls similarly converts the soft, easily closeable neck into a more rigid wedge. Clip blades are more prone to splaying or sliding down the less compressible neck and risk occluding the parent vessel, nearby branches, or adjacent perforating arteries. Protrusion of coils into the aneurysm neck confounds this issue, and may further interfere with permanent clip placement and/or oppose closure. In up to 55% of cases, coils extrude from the aneurysm dome into the subarachnoid space, but coil extrusions are rarely detected on preoperative angiogram (▶ Figs. 35.2 , 35.3 ).
Several morphological parameters may be measured on preoperative angiography to facilitate operative planning—including neck width (N), compaction height (H, which is the distance beneath the compacted coils to the neck of the aneurysm), and the coil width (C), which is the widest diameter of the coil mass parallel to the neck but perpendicular to the direction of anticipated clip application. Prior works have shown that the ratio of coil width to compaction height (C:H), but not the ratio of neck width to compaction height (N:H), is predictive of successful intraoperative clipping.
Workup
Clinical Evaluation
In one clinical series, up to 85% of residual and/or recurrent aneurysms are detected on surveillance angiography. For those who become symptomatic, attention should be paid to symptoms of mass effect—including cranial nerve palsies, focal neurological deficits, seizure, and headache—or symptoms of overt rupture and subarachnoid hemorrhage.
Imaging
Four-vessel digital subtraction angiography is the preferred modality of choice and permits detailed analysis of aneurysm and parent vessel morphology. A computed tomography angiography may also provide additional information regarding partially thrombosed and/or calcified vessels. However, the sensitivity and utility of these techniques may be limited by artifact from the radiopaque coil mass. A noncontrast computed tomography scan of the head should evaluate for potential subarachnoid hemorrhage in any patient presenting with sudden or severe headache with known aneurysm previously treated with endovascular coiling.
Differential Diagnosis
The differential diagnosis for a recurrent aneurysm following initial coiling is limited, but comparison with prior angiograms may help deduce the etiology—including incomplete initial treatment, regrowth, and/or compaction of the coil mass—as this may influence selection of treatment modality. Coil compaction results from a decrease in the interspaces between adjacent coils, whereas regrowth is an increase in aneurysm volume without decrease in coil volume.
Treatment
Choice of Treatment and the Influence of Intracerebral Hematoma
The selection of the appropriate microsurgical or endovascular technique for retreatment of a previously coiled recurrent aneurysm is heavily governed by aneurysm morphology, likelihood for success and durability, physician and patient preference, and surgical candidacy. If the recurrence is small and can be packed densely, coiling may be preferred. However, a second recurrence may occur in 50% of cases with repeated coiling. More sophisticated endovascular techniques—such as stent-assisted coiling and flow diversion with pipeline embolization devices—have shown initial promise, and further work is ongoing to refine their application in previously coiled aneurysms ( 11 in algorithm ). Microsurgical clipping is favored under the following conditions: when the recurrence is larger in size with sufficient tissue in the neck for clip placement; when the predominant mechanism of recurrence is regrowth rather than coil compaction as this excludes the dysplastic tissue; or when there is evidence of coil extrusion (▶ Figs. 35.2 , 35.3 ). Microsurgical clipping offers a more durable solution to available endovascular options ( 5, 8 in algorithm ). A large associated intracerebral hematoma would favor microsurgical treatment—as with untreated ruptured aneurysms—as this would facilitate securing the ruptured aneurysm and enable subsequent evacuation of the clot ( 5 in algorithm ).
The preferred microvascular technique for retreatment of previously coiled residual and/or recurrent aneurysms is direct surgical clipping. Clips should be placed below or against the coil mass to facilitate complete mechanical closure. This configuration prevents refilling, excludes dysplastic tissue, and places the healthy arterial wall tissues in direct apposition to facilitate repair and re-endothelialization ( 5, 8 in algorithm ; ▶ Figs. 35.2 , 35.3 ). In our clinical series, ≥80% of previously coiled aneurysms were successfully treated with microsurgical clipping alone. To predict successful clipping, preoperative determination of the coil width and compaction height (C:H, or compaction ratio) is informative. A compaction ratio ≤2.5 correlates with the likelihood of successful clipping ( 8 in algorithm ). A noncompressible coil mass with a wider coil width and shorter coil height (compaction ratio >2.5) creates a wedge to which the clip is applied. An angle greater than 90 degrees opposes clip closure and increases risk of the downward displacement of the clip to occlude the parent vessel and/or branches. Roughly 70% of all aneurysms with a C:H ratio greater than 2.5 require complex clip reconstruction after thrombectomy or coil mobilization, bypass, and/or wrapping ( 9 in algorithm ). Aneurysms with little coil compaction—a compaction height greater than 2 mm—may not leave enough room to accommodate placement of a clip across its neck, and delay in surgical treatment may allow for further compaction and easier operation at a later date.
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