Clip Ligation of Previously Coiled Aneurysm
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Management of patients with intracranial aneurysms has transitioned to involve experts from both the microsurgical and endovascular realms, who offer the “ideal” intervention based on the best interest of the patient rather than the available expertise of the treating surgeon or interventionist.
Beginning in the 1990s, steady improvements in endovascular techniques and technology have made endovascular modality the first-line therapy for an expanding portion of the patient population suffering from intracranial aneurysms.
Growing support for endovascular intervention has triggered the emergence of a challenging new surgical frontier. Inadequate embolization of a coiled aneurysm poses a risk for aneurysm regrowth sufficient to justify microsurgical intervention. Given the complexity and the unique technical features of clip ligation of recurrent and remnant aneurysms after coiling, I prepared this chapter to review my own and others’ experiences for optimally treating these cases.
Indications for the Procedure
Current literature has demonstrated that both incomplete aneurysm embolization and aneurysm recurrence are risk factors for rebleeding. Therefore, failure to completely embolize the lesion may indicate the need for further treatment. Compaction of the coils and recurrent aneurysms warrant special attention for patients who have a reasonable life expectancy.
Factors associated with residual/recurrent aneurysms or coil compaction after endovascular embolization include a wide aneurysm neck, large/giant aneurysm size, and presence of intrasaccular thrombus. Intraluminal thrombus especially predisposes coiled aneurysms to recanalization.
The patients who undergo coil embolization of their aneurysms are likely to harbor comorbidities and to have aneurysms in less accessible surgical locations when compared with patients who are initially managed via clip ligation. Therefore, as a general rule, patient selection for coiling should be stringent enough so that the risk of operating on previously coiled lesions can be avoided; this strategy is recommended because surgery is associated with many risks in this patient population.
Some patients how have previously undergone coil embolization are reasonable candidates for clip ligation. Indications for clip ligation include:
- patients who were inappropriately selected for initial coiling due to their aneurysm’s morphology or a lack of microsurgical expertise at the institution where they received their initial treatment,
- failure of attempted coiling or recoiling,
- patients who were intentionally managed suboptimally with coiling (only the ruptured lobule was coiled) in an attempt to avoid an open intervention on an “angry edematous” brain associated with a poor clinical grade on presentation,
- symptoms suggestive of aneurysm enlargement or mass effect imposed by the coil mass.
Note that the risk of hemorrhage from the commonly found small aneurysm remnants after endovascular intervention is small and therefore judicious use of microsurgical ligation is warranted.
The presence of the coil mass remarkably affects the operative planning for clip ligation, and I consider three key points:
- I must prepare for potential deleterious effects of the coil mass/intraluminal stent during temporary or permanent clip placement,
- the coil mass usually restricts access to the aneurysm neck, and thereby exponentially increases the technical complexity of clip deployment requiring complex clip reconstruction strategies,
- most importantly, the inflammatory response to the coil mass disrupts the elasticity of the adjacent vascular lining and increases the risk of rupture/ neck avulsion during closure of the clip blades at the interface between the aneurysm neck and the parent artery.
I avoid sac entry and extraction of the coils at all costs. However, there are reasonable, but rare, indications for opening the dome for partial removal of the coil mass so that I can optimize the aneurysm neck for clip application without placing the parent artery at risk.
The aneurysm dome is incised for partial coil removal when any of the following conditions are present: the coil aberrantly projects into the parent artery; the aneurysm recurrence is small (the indication for microsurgery should be questioned); or the mass effect of the coil mass has led to symptomatic compression of the nearby neural structures, including the cranial nerves. In contrast, when the residual neck is 1.5 to twice the width of the clip blades, the neck can be collapsed effectively without the need to open the dome.
During microsurgery, I find that the coil mass has migrated transvascularly and is within the subarachnoid space where it induces an inflammatory response in the surrounding neurovascular structures and complicates planes of dissection. This is a relatively common finding during exploration of partially coiled posterior communicating artery (PCoA) aneurysms; an inflammatory response within or compression on the oculomotor nerve is apparent. The optimal management for these patients is disconnection and resection of the coil mass from the adherent region of the nerve using sharp dissection techniques.
The time interval from the initial coiling to the planned microsurgical intervention is another consideration when planning clip ligation. The friability of the aneurysm neck is a particular concern during the acute period after an endovascular coiling procedure. Following embolization, the neck becomes significantly less mobile and is tethered to the newly embolized dome, potentially increasing the risk of neck tear during clip application. I usually formulate contingency plans, including wider exposure for flexible angles of clip deployment, and prepare for bypass and cotton-clipping techniques.
The relevant cerebrovascular anatomy for an optimal microsurgical approach to these aneurysms can be found within their corresponding chapters in the Aneurysm Subvolume. The previously coiled aneurysm subtypes that are likely to require surgical intervention include:
- distal anterior cerebral artery aneurysms,
- middle cerebral artery bifurcation aneurysms,
- ophthalmic artery aneurysms,
- basilar apex aneurysms.
As discussed previously, the intense inflammatory-mediated response induced by the coils leads to adherence of the aneurysm fundus to the surrounding structures. Standard surgical approaches and normal dissection planes may require intraoperative modification to clarify and expose the aberrant anatomy.
CRANIOTOMY AND APPROACH
Clip application for previously coiled aneurysms may need more expanded exposures and flexible working angles. Basic preparations for a bypass procedure should be made based on the operator’s preoperative suspicion regarding the need for salvage revascularization.
Following an appropriate craniotomy and intradural trajectory to the aneurysm, I attempt placement of temporary occluding clips on the proximal and distal arterial segments that perfuse the aneurysm. Wide dissection of the aneurysm-bearing vessels is imperative because complete aneurysm trapping and flow arrest may be necessary for coilectomy and thrombectomy.
Thorough lysis of the arachnoid adhesions and nearby arachnoid bands tethering the aneurysm-bearing lobe(s) is necessary for securing the additional operative space which traditionally is unavailable for uncoiled aneurysms. This additional space provides me with multiple contingency plans in case of neck tear and torrential bleeding.
Again, the neck and the dome are inspected and released from the surrounding structures. Safe dissection of the coil mass from the points of its adherence is imperative. This maneuver should be performed under high-powered magnification using sharp dissection and may not be indicated if the nerve is placed at risk. Release of the coil mass and the dome will avoid traction on the neck during closure of the clip blades.
Extensive mobilization of the coil mass may also be unavoidable when the coils are causing symptomatic mass effect. If the perforating vessels are engulfed by the mass, important decisions must be made, but I am never embarrassed if I decide clip application is too risky and the procedure is subsequently aborted.
Incising the Dome
There are two general indications for incising the aneurysm dome and attempting coil extraction: 1) symptomatic mass effect caused by the coil mass, and 2) intrusion of the coil mass into the neck and the parent vessel’s lumen, preventing optimal clip placement.
The majority of previously coiled aneurysms that require clipping can be occluded without excision of the coils. Removal of the coils is risky, and can lead to aneurysm neck injury and inevitable parent vessel sacrifice.
I make a generous incision within the fundus parallel to the long axis of the parent vessel. There are two possible approaches for constructing an aneurysm neck to facilitate permanent clip placement.
I mobilize/extract the coils from the dome using a blunt dissector that follows the plane between the coils and the aneurysm wall until the neck is reached without penetrating any of these walls. Proximal and distal temporary occlusion is employed. This instrument can then be used to gently retract the coil mass into the fundus and clear the neck lumen. Next, while the dissector holds the loops of the coils away from the neck, a permanent clip is placed across the neck. Next, the temporary clips are removed and extraluminal verification of the parent vessel’s patency is performed.
A second option for coilectomy may be considered if the technique described above is not deemed effective for clearing the aneurysm neck. In this situation, I attempt to remove a portion of the accessible and movable coil mass to establish partial patency of the aneurysmal neck or soften the neck just enough for clip deployment. Additional removal of the coils may expose the patient to unnecessary risk of ischemia because of an extended period of temporary parent vessel occlusion.
The coil mass should then be transected at the interface of the coil mass with the neck to establish its patency. The use of strong serrated microscissors is advised.
The incision should be started at the coil head and continued circumferentially. The initial incision in the aneurysm can subsequently be extended slightly to facilitate cutting the coils within the neck. It is imperative not to attempt removal of the transected coils until the coil mass within the neck has been completely separated. Pulling on the spaghetti of the coils leads to aneurysm neck injury and unsalvageable walls extending into the parent vessel. Finally, two clips can be used to collapse the neck with minimal coil strands in it.
There are key modifications to these techniques to address the coiled aneurysm’s mass effect. The surgical target is the dome, rather than the neck. First, the dome and the extruded coils are dissected from the surrounding neurovascular tissues. The coils within the fundus are generously cut with serrated microscissors. Some of the embedded strands may be left attached to the surrounding vital structures to avoid injurious operative maneuvers.
The technique of clip placement on the neck of the aneurysms that have been previously coiled is unique in that the clip blades may need to contact a small portion of the parent’s arterial wall and thereby potentially induce mild stenosis within its lumen.
Due to the reduced elasticity of the involved vasculature following coil embolization, there is often limited flexibility about where the clips “like to sit” upon clip deployment. The struggle between where the clip blades tend to rest versus where I want to see the blades rest can potentially lead to a neck tear at the transitional zone where the coils end and the aberrantly rigid parent artery-neck junction begins. “Perfect” clipping is a recipe for catastrophe and a trial clip closure when the neck is insufficiently prepared is fraught with disaster.
Multiple clips are often necessary. Minimal filling of the aneurysm is an acceptable result.
Some patients undergo coiling in an attempt to avoid open intervention on an “angry edematous” brain associated with a poor clinical grade on presentation. In these situations, direct communication between the microsurgical and endovascular specialists is imperative to ensure partial coiling in the appropriate region of the dome or aneurysm lobe so that the risk of future clip ligation is not prohibitive.
Hunterian ligation of the proximal vessels and their trapping/revascularization are important contingency plans for partially embolized aneurysms that are not amenable to primary clip ligation.
Pearls and Pitfalls
- Endovascular intervention for a previously coiled aneurysm is generally preferred instead of a surgical procedure.
- The most common complication of an open intervention for previously coiled aneurysms is a tear at the interface between the partially embolized neck and the parent vessel due to coil-induced reduction in neck elasticity.
- Avoid coil extraction as much as possible.
Contributor: Benjamin K. Hendricks, MD
Rubino PA, Mura J, Kitroser M, Bottan JS, Salas E, Lambre J, Chiarullo M, Bustamante J. Microsurgical clipping of previously coiled aneurysms. World Neurosurg. 2014;82: e203-e208.
Samson DS, Batjer HH, White J, Trammell JT, Eddleman CS: Intracranial Aneurysm Surgery: Basic Principles and Techniques, 1st Ed. New York, Stuttgart: Thieme Medical Publishers, 2011.
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