Aneurysm–Rainbow Team/HelsinkiMicroneurosurgical management of middle cerebral artery bifurcation aneurysms
Introduction
Of the MCA aneurysms, those located at the main bifurcation of the MCA (MbifA) (Table 1) are by far the most frequent [11], [20], [21], [39], [40], [45], [47], [48], [49], [58], [59], [78]. In population-based services, MbifAs are frequent targets of elective surgery (unruptured), acute surgery (ruptured), and emergency surgery (large ICH), even advanced approaches (giant). Middle cerebral artery bifurcation aneurysms are often broad necked and may be dysmorphic in shape involving 1 or both branches of the bifurcation (M2s). The challenge is to clip the neck adequately, without neck remnants, while preserving the bifurcational flow.
This review, and the whole series on intracranial aneurysms, is intended for neurosurgeons who are subspecializing in neurovascular surgery. The purpose is to review the practical anatomy, preoperative planning, and avoidance of complications in the microsurgical dissection and clipping of MbifAs.
This review is mainly based on the personal microneurosurgical experience of the senior author (JH) in 2 Finnish centers (Helsinki and Kuopio), which serve without selection the catchment area in the southern and eastern Finland. These two centers have treated more than 10 000 patients with aneurysm since 1951.
Section snippets
Occurrence of MbifAs
Middle cerebral artery aneurysms are most frequently located at the main bifurcation of the MCA (MbifAs) [11], [20], [39], [40], [45], [47], [48], [49], [58], [59], [78]. Middle cerebral artery bifurcation aneurysms comprised 82.6% of the MCA aneurysms of Yaşargil's series [78]. Table 2, Table 3, Table 4, Table 5 presents the clinical data of patients with MbifA in a consecutive and population-based series of 3005 patients with 4253 intracranial aneurysms from 1977 to 2005 in the Kuopio
Microsurgical anatomical considerations of MbifAs
Middle cerebral artery aneurysms can be classified into proximal (M1A), bifurcational (MbifA), and distal types (MdistA) (Table 1). Proximal MCA aneurysms or M1As are located in the main trunk (M1), between the bifurcation of the ICA and the main bifurcation of MCA [6]. Middle cerebral artery bifurcation aneurysm is the focus of the present article. Distal MCA aneurysm, originating from the M2 or more distal branches of MCA, will be the focus of a separate article.
Middle cerebral artery
Imaging of MbifAs
Digital subtraction angiography is still the present gold standard in many centers. Multislice helical CTA is the primary modality in our centers for several reasons: noninvasive and quick imaging; comparable sensitivity and specificity to DSA in aneurysms larger than 2 mm [9], [17], [25], [33], [35], [61], [64], [65], [70], [72], [73], [74], [76], [80]; disclosure of calcifications in the walls of arteries and the aneurysm; quick reconstruction of 3D images that, for example, show the
Microsurgical strategy with MbifAs
In population-based neurovascular services, MbifAs are frequent targets of elective surgery (unruptured), acute surgery (ruptured), and emergency surgery (large ICH), even advanced approaches (giant). Middle cerebral artery bifurcation aneurysms are also frequent as associated aneurysms. Middle cerebral artery bifurcation aneurysms are often broad necked and may involve one or both M2s. Other branches may be attached to their wall, and, less frequently, perforators may be at risk when
General principles
Usually, it is not advisable to dissect the dome completely before applying the pilot clip, but sharp dissection of the arteries around and adjacent to the base is crucial. M1, M2s, and adjacent and perforating branches near the bifurcation should be unhurriedly, clearly, and painstakingly visualized before final clipping of the MbifA neck (Fig. 8).
Dissection under temporary clipping of arteries
Frequent use of temporary clips allows for safe and sharp dissection of MbifAs and the adjacent arteries. The duration of each temporary occlusion
Intertruncal MbifA
Intertruncal MbisAs project superiorly in the coronal (AP) and posteriorly in the axial plane (Fig. 3). The dome projects to the same direction as the M2 trunks and lies between them. The base is often broad and involves the origin of one M2 (the thicker one) or both. The attachment of M2s to the base and the proximal part of the fundus makes intertruncal MbifAs demanding to clip adequately.
Inferior MbifA
Inferior MbifAs project inferiorly in the coronal (AP) and anteriorly toward the sphenoid ridge, in the axial plane. Consequently, the dome is projecting to the temporal aspect of the surgeon's view inside the sylvian fissure (Fig. 4).
Lateral MbifA
Lateral MbifAs project laterally in the coronal (AP) plane and in the axial plane. In the surgeon's view, lateral MbifAs follow the same direction as the M1 trunk (Fig. 5).
Insular MbifA
Insular MbifA projects medially in the AP (coronal) plane and medially in the axial plane. In the surgeon's view, insular MbifAs project behind the bifurcation, toward the insular surface (Fig. 6).
Complex MbifA
In this special group of dysmorphic and large or giant aneurysms, the growth of the dome is usually multidirectional and the relation of the base with M1 and M2s may be a combination of other types (Fig. 7).
Head positioning and craniotomy should be tailored according to the 3D relation of aneurysm with the bifurcation. After careful dissection, temporary clips are applied to M1 and both M2s. Softened dome may be opened and reshaped by bipolar coagulation (see above). Usually, adequate clipping
Associated aneurysms
Middle cerebral artery bifurcation aneurysms are often associated with other aneurysms, 44% of all patients with MbifA and 30% of those with ruptured MbifA had at least one additional aneurysm (Table 4). Bilateral (mirror) MbifAs were seen in 12% of the patients with MbifA. Our strategy is to clip all aneurysms that can be exposed through the same craniotomy [7], [8], [30], [71], [78]. This may not be advisable if the clipping of the ruptured aneurysm is difficult or the brain is swollen owing
Giant MbifAs
Middle cerebral artery is the most frequent site for giant aneurysms. In the Kuopio series, 4% of all MbifAs and 6% of ruptured MbifAs were giant, with greater than 25 mm in diameter (Table 3). Combined 3D DSA, CTA, and MRI data are necessary for a complete view on the vascular anatomy, intraluminal thrombus, and thickness and calcifications of the wall [21], [55], [60]. In published series, direct clipping was possible in the majority of cases (38%-71%) [14], [15], [27], [28], [29], [36], [41]
Fusiform MbifAs
Often, reconstruction of a fusiform aneurysm may be achieved by clip(s) excluding the “beer belly” from the circulation. For the rest, other techniques like a sling around the aneurysm with a clip and/or wrapping with cottonoids and glue to enhance the scarring have been tried. However, bypass operation followed by occlusion of the parent artery is the treatment of choice.
Bypass operations and arteriotomies
Preoperative high-flow EC-IC or IC-IC bypass using the ELANA or SELANA techniques [54], or low-flow superficial temporal artery–MCA bypass, may be considered in large or giant MbifAs, when the exclusion of the neck from the parent and branching arteries cannot be performed [21]. A comprehensive neurovascular team should be prepared to perform intraoperative arteriotomies, for example, to remove coils or thrombi, and intraoperative EC-IC or IC-IC bypasses, also in case of emergency.
Clipping after inappropriate clipping or failed coiling
The best moment to treat aneurysm is the first moment. Intraoperative verification of clipping by angiography reduces the rate of inappropriate clipping. Scarring after improper clipping or occlusive material inside the aneurysm after failed coiling makes later microsurgical occlusion complicated and sometimes impossible. To reduce redo surgeries, aneurysms should be treated in specialized centers with a high flow of cases and an experienced team mastering exosurgery and endosurgery [34].
Acknowledgments
We thank Mr Ville Kärpijoki for excellent technical assistance.
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2021, World NeurosurgeryCitation Excerpt :On the one hand, the peripheral location of MCA bifurcation aneurysms provides a good microsurgical access. On the other hand, MCA bifurcation aneurysms are often wide-necked and major arterial branches arise at their base (Figure 1), which can pose a challenge for endovascular treatment.6-8 However, with the advances of neurointerventional techniques, a growing number of these aneurysms become amenable to endovascular means.9-11