In the present study, we described 16 cases of SAC treated with the cell-through technique using a single microcatheter (Excelsior SL-10) and a Neuroform Atlas stent in patients with unruptured wide-necked intracranial aneurysms. There was no complication related to delivering or deploying the Neuroform Atlas stent as well as no failure of selecting aneurysms by the cell-through technique. Not the cell-through technique but the jailing technique is our routine method for SAC. However, we found that this cell-through technique might be feasible in patients with small-caliber, stenotic, or very tortuous parent arteries.
Recently, complicated wide-necked aneurysms rather than simple saccular aneurysms have been treated by endovascular methods, but surgeons need more than a single microcatheter to treat those aneurysms. Multiple microcatheter, balloon-assisted, or stent-assisted techniques are needed. For that purpose, surgeons also need a strong and firm guiding catheter to support those devices. A guiding catheter has a very important role in supporting devices being delivered to tortuous intracranial vessels when performing endovascular treatments, including microcatheters, coils, balloons, or stents [5,6,7]. However, when faced with an ICA or VA of small-caliber, with stenosis, or a very tortuous course, it can be difficult to place a 6Fr- or larger guiding catheter to perform multiple microcatheter, balloon-assisted, or stent-assisted techniques. In such cases, a 5Fr- (or smaller) guiding catheter or intermediate catheter would be placed and there will be only one option to use a single microcatheter. Thus, in those situations, we tried to perform SAC with a cell-through technique for wide-necked intracranial aneurysms by using a single microcatheter and a Neuroform Atlas stent.
The Neuroform Atlas stent is the latest version of the Neuroform series reinforcing its navigability in a smaller microcatheter, stability to the vessel wall (high radial force), accurate placement (ease of use with very low foreshortening), wall apposition, conformability, and coil protection. The stent can be delivered via a 0.0165-in. microcatheter, the smallest profile, allowing surgeons to perform SAC with a single microcatheter, a sequential technique where the same microcatheter that is used to place the stent is then used to coil the aneurysm. The cell size of the Neuroform Atlas stent has been reduced compared to that of its predecessor, the Neuroform stent, to achieve better coil protection in aneurysms and to allow the use of smaller coils. Additionally, the width of struts has been reduced so that the flexibility and conformability of the stent are improved. Furthermore, the segmental opening of the struts allows stable positioning and direct vessel wall apposition is obtained by anchoring the stent after the first rows of struts exit the microcatheter. There have been only a few reports on SAC with Neuroform Atlas stents. Most of them reported their preliminary experience with using Neuroform Atlas stents [6,7,8,9,10,11,12,13]. From their experiences with 27 consecutive patients one study concluded that Neuroform Atlas SAC is a feasible way to treat ruptured and unruptured wide-necked aneurysms that are not amenable to conventional coiling or clipping . Aneurysm occlusion and favorable clinical outcomes were consistent with previously reported rates for SAC of wide-neck aneurysms using other devices . From their experiences with 37 aneurysms in 36 patients, another report concluded that deployment of the Neuroform Atlas stent was a safe and effective method for the treatment of wide-necked aneurysms .
Although it is not always easy to advance a microcatheter into an aneurysm using SAC with the cell-through technique, there are some advantages in the use of the Neuroform Atlas stent for the cell-through technique. (1) The closed cells at the proximal end with flaring end give good navigability and enhance the cell-through technique by passing a microwire in the stent lumen easily. When a microwire cannot be advanced through the stent or is stuck in the struts, a microwire looping technique (Fig. 1d and e) provides easy navigation through the inside of the stent lumen. (2) Its open-cell design with both ends flared gives good stability to the vessel wall and wall apposition. It is easy for microcatheters and microwires to pass through the inside of the stent without irritating the struts. Otherwise, microwires cannot be navigated through the inside of the stent. Microwires may go out of the stent lumen, between the struts and the vessel wall, then come back into the stent lumen again. (3) The struts are flexible and reduce stent width. When microcatheter tips cannot be advanced into the aneurysm due to being stuck in the struts, it is possible to overcome the situation by navigating a 0.014-in. microwire through the cell followed by advancement of the microcatheter over the microwire. Pushing the microcatheter very gently against the strut, withdrawing the microwire tip in the microcatheter allows the microcatheter to advance into the aneurysm while overcoming the thin and flexible struts (Fig. 1g and h). (4) It can be delivered via a 0.0165-in. microcatheter that can be easily placed intra-stent space through the pusher wire and easily navigated into an aneurysm sac due to a smaller size of caliber and a less ledge effect. Previous stents can be delivered via a 0.027- or 0.021-in. microcatheter that was difficult to be placed into an aneurysm sac due to a relatively larger size of its caliber and a ledge effect. In some situations, exchange by 0.017 or 0.0165 microcatheter was mandatory in order to use a 0.027- or 0.021-in. microcatheter. A benefit of this cell-through SAC with a single microcatheter method is the possibility to perform SAC using 5Fr-guiding or intermediated catheters, and even when using a 4Fr-intermediate catheter. Another benefit was easy navigation through very tortuous vessels. And, once the aneurysm selection was done by the cell-through technique, then the microcatheter was stuck within a cell of the stent, becoming very stable while inserting coils. Thus, patients with small-caliber, stenotic, or very tortuous parent arteries (ICA or VA) can be good candidates for this technique.
There are some other techniques to perform SAC rather than this cell-through technique. We could perform SAC using two parent arteries with two 5Fr-guiding catheters in each parent artery. First, coil embolization with horizontal stenting could be performed crossing the Circle of Willis [14,15,16,17,18,19]. An aneurysm on the anterior communicating artery or the ICA bifurcation could be treated using a 5Fr-guding catheter each in bilateral ICAs. An aneurysm in the basilar artery aneurysm could be treated using a 5Fr-guding catheter in each ICA and VA. Second, we could perform SAC using a 5Fr-guiding catheter in bilateral VAs to treat aneurysms in the posterior circulation [20, 21]. An aneurysm on the posterior inferior cerebellar artery could be treated using bilateral VAs. However, none of these are universal techniques for SAC. Those techniques can be applied on a case by case basis. Thus, we believed that this cell-through SAC technique with a single microcatheter and a Neuroform Atlas stent might provide neurointerventionists one more option to treat wide-necked intracranial aneurysms with small-caliber, stenotic, or very tortuous parent arteries.
Other low-profile neurovascular stents have been introduced and used clinically, including the braided LVIS Jr. or LEO Baby (Balt, Montmorency, France) that are compatible with a 0.0165-in. microcatheter . These devices can be placed through the same microcatheter needed for subsequent coiling. Thus, they may be used in this cell-through SAC. However, LEO Baby is not available in our country. We have experienced cell-through SAC using LVIS Jr., not intentionally with a single microcatheter but secondarily due to accidental kick-back of the microcatheter while performing SAC with a jailing technique. Thus, we have not performed cell-through SAC using LVIS Jr. with the same single microcatheter.
This study was a retrospective study with a small case series so that the effects of possible selection bias cannot be excluded. However, the cases in the present study could not be done by usual SAC using two microcatheters. Another technique, such as cell-through SAC using a single microcatheter, was inevitable. Thus, it was difficult to have a true control group for evaluating the safety and efficacy of this cell-through SAC technique. In addition, a longer follow-up period is needed to evaluate the true safety and efficacy of this technique. Furthermore, it was challenging to describe the geometry and tortuosity of cerebral arteries in 3D space, because determining uniform measurement standards was difficult. In the present study, we grossly categorized the vessel conditions; parent arteries of small-caliber, with stenosis, or a very tortuous course.