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|Year : 2016 | Volume
| Issue : 4 | Page : 701-702
Endovascular treatment of A1 segment aneurysms
Vivek Singh, Rajendra V Phadke
Department of Radiodiagnosis, SGPGIMS, Lucknow, Uttar Pradesh, India
|Date of Web Publication||5-Jul-2016|
Department of Radiodiagnosis, SGPGIMS, Lucknow, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Singh V, Phadke RV. Endovascular treatment of A1 segment aneurysms. Neurol India 2016;64:701-2
Liu et al., in their article “Endovascular treatment of A1 aneurysms of the anterior cerebral artery” give a detailed description of this entity, a relatively uncommon location for intracranial aneurysm, and its treatment by the endovascular techniques. A1 segment of the anterior cerebral artery (ACA) is between internal carotid artery (ICA) bifurcation and anterior communicating artery (ACOM). These aneurysms are unique as they are generally small sized, multiple, more fragile and associated with vascular anomalies like hypoplasia or aplasia of ipsilateral or contralateral A1 segment, fenestration, duplication and azygous ACA., These complex anatomical variations sometimes make these aneurysms difficult to treat, like the ones associated with fenestration.
The article mentions that A1 segment is significantly important as multiple perforators supplying the anterior commissure, anterior hypothalamus, genu of the internal capsule, and anterior parts of the caudate nucleus and the globus pallidus arise from it. Most of these perforators arise from the proximal part of A1 segment. Between 2-15 in numbers, these are very thin vessels difficult to visualize on a computed tomographic angiogram (CTA) and a digital subtraction angiogram (DSA)., Aneurysms arising from the proximal A1 segment are commonly associated with perforators and the middle segment gives origin to either fusiform or dissecting aneurysms. Aneurysms associated with anomalies like fenestrations or duplications arise because of direct hemodynamic stress at the bifurcation ends either at the proximal or the distal segment.
The authors highlight that the complexity of these aneurysms increases when a significant sized perforator is arising from the base or fundus of the aneurysm. The authors state that most of these aneurysms are small in size and treating them selectively with sparing of the perforator is technically challenging for both endovascular coiling and neurosurgical clipping. Dissecting aneurysm in this segment is not very common and have a distinct angiographic appearance as described in this article which includes irregular segmental stenosis, irregular fusiform or aneurysmal dilation, and retention of contrast agent. Most of these A1 segment aneurysms are posteriorly directed due to which they are obscured by the parent vessel and may necessitate a repeat angiogram as reported earlier. Recent advances in the imaging techniques such as three dimensional (3D) reconstruction images of CTA, which are reviewed in different planes on a workstation, hardly leaves a chance of missing any aneurysm in this segment. However, this is subject to the reviewer's experience. Utility of 3D rotational DSA in detecting small aneurysms has been previously reported.
This article has very well described the morphology of aneurysms and the importance of neck dome ratio which guides the endovascular strategies like simple coiling or using remodeling techniques in the form of balloon or stent assistance. This study included both ruptured and unruptured aneurysms and it is mentioned that ruptured aneurysm were small when compared to unruptured aneurysm. We feel that treating small unruptured aneurysms definitely needs a more considered decision depending on the institutional policy and clearance from the local ethical committee. Use of modified Rankin scale (mRS) before treatment is questionable as this score is a disability score which should be used at the time of discharge and further follow-ups. The article mentions about coil protrusion into a distal branch of the middle cerebral artery in one patient, and the coil was salvaged by a 4-mm × 15-mm solitaire stent. This may actually be better described as coil migration.
This article has very well reviewed the literature available for the A1 segment endovascular embolisation methods, its complications, success rate and follow-ups.
In a recent review of our data of the last 199 aneurysms treated by endovascular means, we had 4 patients with a ruptured A1 segment aneurysm. Of these aneurysms, two were more than 10mm in diameter; larger aneurysms are, therefore, not very uncommon in this segment. We performed a simple coiling of all these aneurysm with a good outcome. One of the cases, in whom a large ruptured aneurysm arising from the distal A1 segment was associated with duplication, where we did a simple coiling, had a good outcome. His preoperative and follow up magnetic resonance angiogram image is shown in [Figure 1]a,[Figure 1]b,[Figure 1]c. This case also suggests that aneurysms, when associated with anomalies of the A1, usually arise from the ends of the fenestrated/duplicated vessels. In our case, it arose from the proximal end of the duplication. With recent advances in endoluminal techniques, small unruptured blister/bleb or fusiform aneurysms of this segment will be managed by placing a small sized flow diverter like the pipeline (ev3, USA) or FRED Jr (Microvention USA) device.,
|Figure 1: (a) Postero inferiorly directed large aneurysm (>10mm diameter) arising from A1 segment with suspicious duplication (arrow), coiling of the aneurysm done. (b) The coil mass with no obvious filling of the aneurysm. Followup MRA done after 6 months show no filling of the aneurysm with arrows showing the duplicated segments (c)|
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The authors would also like to mention the use of MRA for the preliminary assessment at follow-up of these patients, as undertaken currently in many institutions. Though DSA is the gold standard, MRA is a practical and a noninvasive method to assess for aneurysm recanalisation and allows for a long term follow-up, at a very low risk.
Endovascular treatment in this segment has an upper hand to neurosurgical clipping. Although previously a major treatment option, surgery in these aneurysms does pose certain difficulties. At surgery, adequate mobilization of the vessel before proper visualization of aneurysm is required as most of these aneurysms are obscured by the parent vessel; and, sometimes these aneurysms are embedded within the frontal lobe which needs retraction of the frontal lobe further increasing the risk of intraoperative rupture. Endovascular treatment on the other hand, poses less complexities and is feasible in most of the cases. A1 segment vasospasm may pose a difficulty in a ruptured aneurysm; however, it can be managed by appropriate nimodipine infusion. We congratulate the authors for their work and for presenting a comprehensive review of the subject.
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