Key-words: Aneurysm - coil embolization - clipping - cranial bypass - giant aneurysm - revascularization
Introduction
Postembolization recurrent aneurysms occur significantly in patients with intracranial
aneurysms treated by coil embolization.[[1 ]] Aneurysms occurring at the proximal A1 segment of the anterior cerebral artery
(ACA) are uncommon, constituting 1%–4% of intracranial aneurysms. Giant aneurysms
in this location are very rare.[[2 ]],[[3 ]] Endovascular coil embolization has been noted to be effective in small aneurysms
and has been considered an effective treatment modality for A1 aneurysms. However,
aneurysms arising from A1 are usually small, with a fragile wall and are often treated
by microneurosurgical clipping.[[3 ]] There is scanty information about the effectiveness of either method for giant
aneurysms of A1.
Recanalization of aneurysms is more common with giant aneurysms and aneurysms in the
posterior circulation with reported recanalization of 12%–54% of cases.[[4 ]],[[5 ]],[[6 ]],[[7 ]],[[8 ]] Tight coil packing with a density of at least 20%–25% is known to be generally
important for preventing recanalization after embolization of cerebral aneurysms.
Large aneurysms sometimes recanalize regardless of the packing density, suggesting
that the absolute residual volume which is determined by aneurysm volume and packing
density may be a more important risk factor for recanalization.[[9 ]]
Case Report
The following is a case of recurrent ACA A1-segment giant aneurysm which recanalized
postcoil embolization in a 60-year-old male. The first coiling was done 3 years earlier
after rupture when he presented with subarachnoid hemorrhage of world federation of
neurosurgical societies (WFNS) Grade 5. The aneurysm measured 26 mm in widest dimension.
This was followed by ventriculoperitoneal shunt insertion for posthemorrhage-related
progressive hydrocephalus 5 months later. The patient had to undergo second coiling
11 months after the first coiling because of recanalization, which again had to be
redone after 6 months because of continued refilling. Despite the three coiling procedures,
the repeat angiography confirmed the aneurysm had recanalized. An infarct is noted
in the left frontal lobe on the computed tomography scan which occurred after the
initial bleed [[Figure 1 ]]. The patient became hemiparetic as a result.
Figure 1: (a) A coronal computed tomography scan view of the brain with the coil in situ, (b)
computed tomography scan of the brain showing the shunt in situ and a left anterior
cerebral artery territory infarct, (c) threedimensional computed tomography scan showing
the STA artery, (d) a brain computed tomography reconstruction, three-dimensional
brain computed tomography angiogram scan with the aneurysm showing the mass of coils,
(e) shows the aneurysm filling on digital subtraction angiography and it is incompletely
occluded, and (f) the aneurysm measuring 26.1 mm x 23.8 mm
The patient was scheduled for left superficial temporal artery (STA) to ACA-A3 bypass
with clip occlusion of the ACA ipsilaterally distal to the aneurysm before the anterior
communicating artery. The strategy was to prevent further recanalization of the aneurysm,
allowing for aneurysm thrombosis.
With the patient in supine position and the head turned 30° to the right on a Sugita
frame, a curvilinear incision was made just behind the hairline, and the posterior
(parietal) branch of the STA was isolated and prepared as the graft while fashioning
a frontotemporal craniotomy. By microdissection, the carotid bifurcation and its branches,
with the adjacent giant A1 aneurysm were exposed. Embolization coils were found lying
outside the aneurysm [[Figure 2 ]]a and [[Figure 2 ]]b.
Figure 2: (a) Detailed intraoperative views seen at exposure of the aneurysm, (b) the extruded
coils, (c) an illustration of the craniotomy done, (d) the bypass anastomosis, (e)
a dual intraoperative visualization approach picture showing the patent graft just
before the closure, and (f) graphic illustrative summary of the operation procedure
done
Adjacent frontal craniotomy was done in the parasagittal area to expose the A3 branches
of the ACA [[Figure 2 ]]c. The patient's initial position needed just minor bed rotation to allow for the
second osteotomy and anastomosis procedure without redoing the frame positioning.
The STA-ACA bypass was done where the STA was anastomosed to the A3 segment of ACA
(pericallosal artery) from the interhemispheric, supra-callosal area. The proximal
segment of ACA A1 segment could not be accessed because it was very short and continued
manipulation created a risk of serious hemorrhage over the bifurcation of the carotid,
which was noted to be atherosclerotic and with the short proximal segment being partially
occluded by coils. There was no place for clip placement. The distal A1 segment was
then occluded distally by clip ligation just proximal to the anterior communicating
artery. To maximize on patient safety, motor-evoked potentials, indocyanine green,
and dual-image video angiography were used during the procedure for safety monitoring
[[Figure 2 ]]e.
Discussion
Postembolization recurrent aneurysms have been reported several times in patients
with intracranial aneurysms treated by embolization. In 2007, Tirakotai et al. classified
the indications for surgical treatment after the coiling of aneurysms into the following
three groups: (i) surgery of residual and recurrent aneurysms, (ii) surgery for mass
effects on neural structures due to coil compaction, and (iii) surgery for vascular
complications after endovascular procedures.[[1 ]],[[10 ]]
Retreating a recurrent aneurysm with additional coils is often bound for failure,
in perhaps 50% of cases and it seems reasonable to offer something different than
what was initially done to hope for better results.[[11 ]] Proper patient selection for either coiling or clipping is important to avoid recanalization
in the first place. Our patient had had coiling done three times and another treatment
option, therefore, needed to be explored. Our patient was type III recanalization
since the coils were partially occluding the vessel and the coils were also extruded
outside the vessel. The narrowed vessel lumen caused by presence of the intraluminal
coils coupled with atherosclerosis on a site with medial thalamostriate perforators
precluded endovascular stenting with devices such as the flow diverting stents because
of the increased risk both of injury to the main vessel and of occlusion of the perforators.[[12 ]]
Some surgeons have advocated for clipping of the partially coiled aneurysm. Difficulties
have, however, been reported because of the high risk of rupturing of the aneurysm
during the clipping. In some cases, aneurysm trapping with occlusion of the proximal
and distal segments relative to the aneurysm has been done.[[10 ]] In this case, aneurysm clipping could not be done because of the very wide neck
containing coils over a thickened wall. Proximal A1-segment occlusion could not be
done because of the very small length of the segment which was inaccessible without
posing a danger of rupturing the aneurysm or tearing the carotid bifurcation. Occlusion
of A1 distal to the aneurysm and revascularization surgery through STA-A3 was, therefore,
planned. Clip occlusion of the parent vessel with bypass revascularization protection
of the brain has been well described before though the various series described proximal
occlusion instead.[[1 ]],[[5 ]],[[10 ]],[[11 ]],[[12 ]],[[13 ]],[[14 ]],[[15 ]]
Our patient had revascularization with STA-A3 segment anastomosis [[Figure 2 ]]d. Revascularization was important to ensure continued blood flow distal to the
arterial occlusion after clipping. Occlusion with no plan for revascularization was
going to risk the brain from infarction. The area getting revascularization had suffered
an infarct before. This was delayed revascularization with less chance of revascularization
injury.[[16 ]],[[17 ]] Aneurysm trapping was too risky and was, therefore, not done because of the risk
of rupture and infarction in the distribution of the perforators involved. Distal
A1-segment clipping was done as a way of stopping continued flow. Recoiling of the
aneurysm to fill up the space is expected to result in complete obliteration of the
aneurysm, thereby minimizing the risk of regrowth of the aneurysm. This technique
may solve the perforator vessel ischemia problem that has been experienced with giant
aneurysm trapping.[[18 ]] This, however, still has the potential risk which still needs to be evaluated for
possible growth of the aneurysm.[[19 ]]
The posterior branch of the STA was used as the graft. This is because this was the
longer and bigger branch of the artery as seen in [[Figure 1 ]]c. The posterior branch of the STA has been described in the literature as being
usually the bigger and longer branch of the two terminal branches of STA, as it goes
to anastomose its branches with the contralateral one.[[20 ]],[[21 ]] It, therefore, provided enough length to reach the A3 segment of the ACA without
requiring an interposition graft. The blood flow will continue into the territory
of the obliterated vessel through the preserved anterior communication artery and
the revascularization [[Figure 2 ]]f. Current literature describes anterior circulation bypass as from STA to middle
cerebral artery or internal carotid or the use of interposition grafts on doing STA
to ACA bypass.[[22 ]],[[23 ]],[[24 ]] While A3 to A3 ACA revascularization has been described, its ability to supply
enough blood bilaterally was doubtful because of the atherosclerotic changes noted
at surgery in the carotid arteries.[[25 ]]
This case is an illustrative case of successful direct use of the STA-ACA bypass for
revascularization where there is a need for vessel occlusion on A1, thereby obviating
the risk of brain ischemia.
Conclusion
A combination of STA-A3 segment revascularization with distal A1-segment clipping
is a treatment option for the A1 aneurysms that reoccur post coiling for SAH from
a giant A1 aneurysm. This is especially useful where the anterior communicating artery
cannot provide enough flow. Further evaluation will be needed to assess for the sustainability
of this treatment option over time.
