Keywords

In general, vertebro-basilar aneurysms are good indications for endovascular treatment [2, 5, 6]. However, basilar bifurcation (BA-bif) aneurysms, BA-superior cerebellar artery (BA-SCA) aneurysms, and sometimes mid-basilar aneurysms are also good indications for this procedure [4, 9]. On the other hand, surgical clipping is relatively contraindicated for elderly patients, in particular those in poor clinical condition, as well as for large or giant aneurysms.

There are several important things to keep in mind in operative planning for BA-bif and BA-SCA aneurysms; these include projection of the dome, height of bifurcation, or distance from the neck of the aneurysm to posterior clinoid process, size of the neck, location of the perforators, origin of the neck, size of posterior communicating (Pcomm) artery, etc. The aneurysms where the neck is 5–10 mm above the clinoid line are suitable for a pterional approach [3] (Fig.1, upper left).

Fig. 1
figure 1

Upper left: Surgical approaches according to height of bifurcation or neck of basilar distal aneurysm relative to posterior clinoid. Upper right: Surgical routes for the distal basilar aneurysms when pterional craniotomy is selected. Lower left: Intra-operative photographs of Case 1. Lower right: Intra-operative photographs of Case 2

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BA-bif and BA-SCA aneurysms can be approached using pterional craniotomy. A basilar top complex that looks like a dragonfly appears when Liliequist's membrane is opened, and the optimal route to the aneurysm’s neck, lateral to internal carotid artery (ICA), medial to ICA, or posterior to ICA, is selected (Fig. 1, upper right).

There are several tips for clipping distal BA aneurysms [1]. Superficial Sylvian and frontobasal veins must be preserved. Proximal control at the proximal BA should be prepared, in particular, when the height of the neck is low or the size of the aneurysm is large. It is very useful to soften the dome during neck dissection and clip placement. For emergent control for intra-operative rupture, proximal control of BA is absolutely necessary. For this purpose, posterior clinoidectomy is sometimes carried out. The drilling during the posterior clinoid process must be done meticulously. Retraction or division of the anterior tentorium is sometimes effective for proximal control of BA. Perfect clipping must be carried out after the BA-complex is confirmed. After surgical clipping, it is important to verify that the aneurysm is excluded, perforators are patent, and P1 and SCA are patent.

Several representative cases are shown here.

  • Case 1 is a 60-year-old female who suffered from a subarachnoid hemorrhage (SAH). Her clinical grade was IV according to WFNS grading. Surgical clipping for BA-bif An was carried out 10 days after the onset of SAH (Fig. 1, lower left).

  • Case 2 is a 65-year-old female who suffered from SAH. First, endovasucular coiling was carried out. Follow-up angiograms revealed a neck remnant, so clipping for BA-bif aneurysm was performed (Fig. 1, lower right).

  • Case 3 is a 65-year-old female who suffered from SAH; a ruptured distal anterior cerebral artery aneurysm was successfully clipped. Surgical clipping for an unruptured BA-bif aneurysm was carried out (Fig. 2, upper left).

    Fig. 2
    figure 2

    Upper left: Intra-operative photographs of Case 3. Upper right: Intra-operative photographs of Case 4. Lower left: Intra-operative photographs of Case 5. Lower right: Intra-operative photographs of Case 6

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  • Case 4 is a 47-year-old male who suffered from SAH. His clinical grade was II according to WFNS grading. Surgical clipping for a BA-trunk aneurysm was carried out 1 day after the onset of SAH (Fig.2, upper right). In this case, posterior clinoidectomy was carried out.

  • Case 5 is a 50-year-old female. Surgical clipping was done for her unruptured L.BA-SCA aneurysm (Fig. 2, lower left)

  • Case 6 is a 45-year-old female who suffered from SAH. Her ruptured middle cerebral artery aneurysm was successfully clipped. Surgical clipping for unruptured BA-SCA aneurysm was performed (Fig. 2, lower right).

  • Case 7 is a 59-year-old female who suffered from SAH and had been admitted to another hospital. CTA and DSA revealed a partially thrombosed BA-SCA aneurysm (Fig. 3, upper left). Coil embolization was performed immediately. A follow-up DSA showed refilling of the neck, so a second coil embolization was performed. However, the neck of the aneurysm was not completely obliterated (Fig. 3, upper right). The patient was referred to our hospital. We decided that her BA-SCA aneurysm was a relatively good indication for surgical clipping. A DSA taken the day before the craniotomy shows refilling of the neck. The neck of the aneurysm seemed to have enough space for clipping (Fig. 3, upper right) so we decided not to remove coils in the arterial lumen.

    Fig. 3
    figure 3

    Upper left: CT and DSA of Case 7. Upper right: Follow up DSA of Case 7. Lower left: Intra-operative photographs of Case 7. Lower right: Intra-operative photograph and Postoperative MRI and DSA of Case 7

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A modified right orbito-zygomatic temporo-polar approach [7, 8] with both anterior and posterior clinoid removal was chosen. Surgical clipping seemed to be carried out without any problems (Fig. 3, lower left). The patency of SCA was confirmed by micro-Doppler ultrasonography. An intra-operative ICG-VA was done after placing the clip and it revealed a patent SCA. The next day, however, a high intensity area was noted in the cerebellum on DWI (Fig. 3, lower right). Two possible reasons for this were given: clipping of the aneurysm resulting in stenosis of the SCA, or a placed clip moved toward a BA. To avoid these complications, confirmation of the patency of SCA by intra-operative DSA or placing the final clip after coil removal are recommended.

Conclusion

There are several TIPS for the clipping of distal BA aneurysms. Among them, the following are very important for safe and secure clipping: First of all, patency of the perforators, P1, and SCA must always be maintained. Several modalities including micro-Doppler ultrasongraphy and ICG-VA should be used to confirm patency of these vessels. Each confirmation of patency of the vessels after clipping must be compared to those before clipping. Intra-operative DSA is necessary for large or giant aneurysms.