Endovascular navigation past some large or giant intracranial aneurysms for the purpose of stent deployment can be difficult. Some of these lesions have a morphology which compels the operator to navigate through the aneurysm dome in order to gain distal access, a step which requires straightening of the delivery microcatheter before a stent can be deployed. In most patients this can be achieved by simply retracting the microcatheter and reducing the loop within the aneurysm. However, in certain patients the acute angle formed between aneurysm inflow and outflow tracts as well as the dynamics of tension within the microcatheter act together to prevent this from happening. Instead of retracting and straightening across the aneurysm neck, the microcatheter withdraws leaving the intra-aneurysm loop intact. This challenge can thwart attempts at stent placement and subsequent embolization. The authors describe a simple and safe technique to circumvent this problem, a way of stabilizing the distal tip of the microcatheter which they term the ‘sea anchor’.
Statistics from Altmetric.com
Stressing the wall of an aneurysm is best kept to a minimum under any circumstances, whether or not it is ruptured. When a large aneurysm must be included in the navigation route for distal access—that is, rather than being bypassed—this is best done with a light weight microcatheter rather than the larger medium-sized microcatheters used for stent delivery. We suggest navigating through the aneurysm with a conventional microcatheter such as Excelsior SL10 (Boston Scientific, Natick, MA, USA) or Prowler (Codman Neurovascular, Raynham, MA, USA) and a 0.014 inch wire. Sometimes this is not easy to do, but when the catheter is being advanced over the wire the lighter construction of the smaller microcatheter probably makes this component of the procedure much safer.
Once distal access with the microcatheter has been gained and it becomes evident that attempts to straighten the microcatheter across the mouth of the aneurysm are failing due to back-slippage of the microcatheter, rather than eliminating the aneurysmal loop we employ the ‘sea anchor’.
After removal of the wire, a 30 cm aneurysm coil is paid out through the microcatheter into the distal vessel as much as possible with the detachment zone of the coil kept proximal to the aneurysm. By locking down on the delivery wire of the coil with the rotating hemostatic valve (RHV), the relationship of the coil and microcatheter is fixed. The microcatheter can then be retracted and the distal coil will stabilize the distal tip by creating sufficient drag that the microcatheter tip no longer retracts. By keeping the intra-aneurysmal component of the microcatheter filled with coil too (hence the reason for using such a long coil), no additional tensile strength is lent to the microcatheter loop within the aneurysm, thus maximizing the softness of this segment and encouraging the unfolding to take place. Once the microcatheter has been straightened across the mouth of the aneurysm, an exchange-length wire can be advanced and the microcatheter can be replaced with a larger-bore device such as a Renegade Hi-Flo or Marksman microcatheter for stent delivery.
In the same way that a sea anchor is thrown overboard to increase drag and stabilize a boat in heavy seas, the soft coil deep within the distal vessel creates drag against the adjacent endothelium. Using a soft coil ensures the resistance is achieved with minimal risk of endothelial injury. The ‘sea anchor’ coil is subsequently removed and resheathed, to be used later during embolization.
A woman in her 50s with a giant basilar apex aneurysm was evaluated for endovascular treatment. Because of an acute angle between the inflow and outflow tracts of the aneurysm, the decision to attempt a stent-assisted coil embolization procedure was made.
A 6 F Envoy guide catheter (Codman Neurovascular, Raynham, MA, USA) was advanced into the proximal left vertebral artery. An Excelsior SL-10 microcatheter (Boston Scientific, Natick, MA, USA) and 0.014 inch Synchro2 soft wire (Boston Scientific) were passed through the guide catheter and carefully navigated through the aneurysm. Primary bypass of the aneurysm neck was attempted but was unsuccessful as the wire became looped in the aneurysm dome before finding the outlet vessel and extending into the right posterior cerebral artery. Attempts to reduce the loop and straighten the microcatheter across the aneurysm neck were unsuccessful as the Synchro2 soft wire did not afford a stable distal purchase.
The Synchro2 soft wire was removed from the microcatheter and a long soft detachable coil (Target 10 mm×30 cm; Boston Scientific) was advanced deep into the distal right posterior cerebral artery. Care was taken to ensure the stiff detachment site of the coil remained proximal to the aneurysm dome. With the coil acting as a ‘sea anchor’, gentle traction was applied to the microcatheter and the redundant loop within the dome of the aneurysm was straightened (figure 1). The coil was then removed and resheathed.
An exchange length 0.014 inch Balance Middleweight Wire (Abbott Vascular, Abbott Park, IL, USA) Guidant Corporation (Indianapolis, IN, USA) was then placed distally in the right posterior cerebral artery through the Excelsior SL-10 microcatheter. In an exchange procedure, the SL-10 microcatheter was removed and replaced with a Marksman microcatheter (ev3 Endovascular Inc., Plymouth, MN, USA). A self-expanding 3.5×30 mm Neuroform EZ Stent (Boston Scientific) was then deployed across the aneurysm neck from the basilar artery into the right P1 segment (figure 2).
Once the stent was determined to be in a satisfactory position, the aneurysm was carefully catheterized and embolized with numerous 10 mm coils of Target and Galaxy manufacturing type, including the previously used ‘sea anchor’ coil. A post-procedure angiogram demonstrated satisfactory obliteration of the aneurysm lumen.
Large wide-necked aneurysms remain technically challenging lesions to treat with complication-ridden endovascular and microsurgical approaches. Many advanced endovascular techniques have been described for the treatment of giant aneurysms to include balloon remodeling,1 ,2 intrasaccular coil and Onyx embolization, stent-assisted coil and Onyx embolization and covered stent placement.3 ,4 The techniques which rely on primary coiling often lead to suboptimal occlusion and high recurrence rates.5–10 Because of the complex architecture and internal flow dynamics of giant aneurysms, flow diverting techniques with the use of intravascular stents are becoming a preferred method of treatment.
To use a flow diverting method, stable distal access across the aneurysm neck must be achieved so that a stent may be deployed. This step is complicated in a subset of aneurysms which are characterized by an acute angle between the inflow and outflow vessels. This feature and the resulting dynamics of tension within the microcatheter necessitate the formation of a redundant loop in the microcatheter and wire assembly. Straightening this loop across the aneurysm neck is often problematic due to a lack of stable distal purchase.
Previously described techniques to address this problem include a ‘balloon anchor’,11 ,12 ‘double wire’13 and ‘stent anchor’14 technique. The ‘balloon anchor’ and ‘stent anchor’ techniques rely on the ability to pass a balloon catheter or stent assembly across the aneurysm which is not always a safe or feasible option in a subset of these lesions, which are at times delicate and prone to rupture. The ‘double wire’ technique is a direct bypass method which is also at times impossible because of the acute angle microcatheters must sometimes traverse in order to gain distal access.
The ‘sea anchor’ technique allows a lightweight microcatheter to pass across the acute angle of a giant aneurysm by using a long soft coil within the distal vessel to create stable distal purchase (figure 3). This technique allows the giant aneurysm to be safely traversed with minimal risk of rupture or endothelial damage.
We have not experienced any complication using this method. This technique provides another tool to aid in stent placement across the neck of giant aneurysms, a critical step in current state-of-the-art endovascular management of these challenging lesions.
Contributors PPM had the idea for the article, performed the literature search, wrote the article and acts as guarantor. LE and GK performed the literature search and wrote the article.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.