PEER-REVIEW REPORTS

Prevention of Retrograde Blood Flow Into Large or Giant Internal Carotid Artery
Aneurysms by Endovascular Coil Embolization with High-Flow Bypass: Surgical
Technique and Long-Term Results
Norio Nakajima1, Shinji Nagahiro1, Junichiro Satomi1, Yoshiteru Tada1, Kohei Nakajima1, Shu Sogabe1,
Mami Hanaoka1, Shunji Matsubara2, Masaaki Uno2, Koichi Satoh3

Key words

- BACKGROUND: Recanalization has been reported in large or giant aneurysms

- Coil embolization

of the internal carotid artery (ICA) addressed by high-flow bypass and endovascular treatment. Aneurysmal recanalization may be attributable to retrograde
blood flow into the aneurysm through the ICA branches, such as the ophthalmic
artery or the meningohypophyseal trunk, or through the surgically created bypass.
We modified the endovascular treatment of aneurysms to prevent retrograde flow
and evaluated the long-term efficacy of our method.

- Giant aneurysm
- High-flow bypass
- Internal carotid artery
- Retrograde blood flow

Abbreviations and Acronyms
BTO: Balloon test occlusion
CCA: Common carotid artery
ECA: Extracranial artery
ECeIC: Extracranial-to-intracranial
ICA: Internal carotid artery
ISUIA: International Study of Unruptured Intracranial
Aneurysms
M2: Middle cerebral artery second portion
MCA: Middle cerebral artery
MHT: Meningohypophyseal trunk
MRA: Magnetic resonance angiography
MRI: Magnetic resonance imaging
OphA: Ophthalmic artery
RA: Radial artery
STA: Superficial temporal artery
From the 1Department of Neurosurgery, Institute of Health
Biosciences, Tokushima University, Tokushima; 2Department
of Neurosurgery, Kawasaki Medical School, Okayama; and
3
Department of Neurosurgery, Tokushima Red Cross
Hospital, Tokushima, Japan
To whom correspondence should be addressed:
Shinji Nagahiro, M.D., Ph.D.
[E-mail: nagahiro.shinji@tokushima-u.ac.jp]
Citation: World Neurosurg. (2015) 83, 6:1127-1134.
http://dx.doi.org/10.1016/j.wneu.2015.01.037
Journal homepage: www.WORLDNEUROSURGERY.org
Available online: www.sciencedirect.com
ª 2015 The Authors. Published by Elsevier Inc. This is an
open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/)

INTRODUCTION
Various treatment options have been reported for patients with large or giant
complex aneurysms arising from the C2eC4
segment of the internal carotid artery (ICA).
However, because of their large size, difficult
location, wide atheromatous neck, and
calcified dome, some aneurysms are unclippable and the intracranial approach is
contraindicated. Endovascular techniques to

- METHODS: We used

a hybrid operative/endovascular technique to treat 5
patients with large or giant aneurysms arising from the C2eC4 segment of the
ICA who presented with visual symptoms due to the mass effect of the aneurysm.
To prevent retrograde flow into the aneurysm our modified endovascular treatment involves coil embolization of the aneurysmal orifice and the ICA, including
the origin of the ophthalmic artery and meningohypophyseal trunk, and placement of a high-flow bypass using a radial artery graft.

- RESULTS: During the 5- to 12-year follow-up period, 4 aneurysms disappeared,

and the other decreased in size. There were no subarachnoid hemorrhages. All
bypass grafts remained patent. Visual preservation was achieved in 2 patients; 1
patient manifested visual improvement. Although 2 patients experienced transient
neurological deficits we encountered no permanent complications in this series.
The final modified Rankin scale of the 5 patients was 0 or 1.
- CONCLUSIONS: Prevention

of retrograde flow into the aneurysm by coil
embolization with high-flow bypass is a safe and effective method. It prevents
the recanalization of large or giant ICA aneurysms.

address cerebral aneurysm are available and
stent-assisted coil embolization and special
stents including covered and flow-diverting
stents, such as pipeline stents, are useful
for treating giant ICA aneurysms (5, 21).
Becske et al. (5) showed that at 1-year followup, 87% of their large or giant ICA aneurysms
were completely occluded. However, unstable scaffolding, intraparenchymal hemorrhage unrelated to rupture of the target
aneurysms, and thromboembolic complication requiring prolonged dual antiplatelet
therapy remain an unsolved problem (20).
Although ligation of the cervical ICA
with or without extracranial-to-intracranial
(ECeIC) bypass is available to address
unclippable aneurysms, their recanalization and rupture have been reported

WORLD NEUROSURGERY 83 [6]: 1127-1134, JUNE 2015

(10, 12, 13, 15, 17). Proximal ICA occlusion
does not exclude aneurysms from the flow
stream and retrograde flow into the aneurysm may be related to aneurysmal recanalization. There are two collateral pathways into
aneurysms, the intrinsic collateral routes
between the extracranial artery (ECA) and the
ICA through ICA branches, such as the
ophthalmic artery (OphA) or the meningohypophyseal trunk (MHT), and retrograde
flow from the surgically created bypass graft.
To avoid recanalization due to retrograde
flow into the aneurysms, in our 5 patients
we performed endovascular coil occlusion
of the aneurysmal orifice and the ICA,
including the origin of the OphA and MHT.
We placed a bypass (radial artery [RA] to
second portion [M2] of the middle cerebral

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PREVENTION OF RETROGRADE BLOOD FLOW

artery) before endovascular coil occlusion.
We report our operative techniques and the
long-term outcomes in these 5 patients.
METHODS
Patients
Between January 1996 and June 2011, 18
consecutive patients with large or giant ICA
aneurysms were treated in our department.
The treatment strategy for each patient
was decided by neurovascular surgeons
and endovascular specialists. Of the 18
patients, 5 underwent coil embolization of
the aneurysmal orifice and the ICA
including the origin of the OphA and MHT
and placement of a high-flow bypass using
an RA graft.
The 5 patients presented with large or
giant ICA aneurysms (C3eC4 cavernous
aneurysms, n ¼ 3; C2eC3 paraclinoid
aneurysms, n ¼ 2) and dysfunction of
cranial nerve II (n ¼ 2), III (n ¼ 2), and/or
VI (n ¼ 3) due to compression by the
aneurysms. One patient (case 2) had a past
history of subarachnoid hemorrhage due to
rupture of a contralateral ICA aneurysm that
had been clipped earlier. The aneurysms
were giant in 4 patients and large in 1; their
sizes ranged from 15e43 mm.
All patients underwent ICA balloon test
occlusion (BTO) to identify those at risk
for acute ischemia related to the temporary
occlusion of the middle cerebral artery
(MCA) during the high-flow bypass
procedure. Although all patients were
BTO-tolerant, had our series including
BTO-intolerant patients, we would have
placed a double-insurance bypass (i.e., the
superficial temporal artery [STA]eMCA
bypass before the introduction of the highflow bypass to reduce the risk of ischemic
complications) (9). A high-flow bypass
using an RA graft was placed in all patients
to prevent hemodynamic ischemia in the
ipsilateral hemisphere and the development
of de novo aneurysms.
Surgical Technique
Schematic drawings of our operative techniques and steps are shown in Figures 1
and 2. Neurophysiological monitoring to
identify possible cerebral ischemic damage
during temporary clipping included
somatosensory-evoked and motor-evoked
potentials. Craniotomy, exposure of the
carotid artery, and harvesting of the RA were

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Figure 1. Illustration depicting the high-flow bypass using a radial artery (RA)
graft between the external carotid artery (ECA) and the second portion (M2)
of the segment of the middle cerebral artery. For intraoperative coil
embolization of the internal carotid artery (ICA) proximal to the aneurysm
(AN) a 7F sheath and a balloon catheter were inserted into the ICA.

performed simultaneously by 3 teams of
neurosurgeons. A 15- to 17-cm long segment
of the RA was harvested between the wrist
and the elbow. Before use, the harvested
graft was distended in heparinized saline to
avoid twisting and kinking. The common
carotid artery (CCA), ICA, and ECA were
exposed by making a cervical incision along
the anterior aspect of the sternocleidomastoid muscle. Pterional craniotomy was performed with wide dissection of the Sylvian
fissure.
Next, the harvested RA graft was passed
from the cervical- to the craniotomy side
through an 18-gauge chest tube in a tunnel
created under the mandible and zygomatic
arch (Figure 1). Distal anastomosis between
the distal end of the RA and M2 was
performed first in an end-to-side fashion
with 9-0 monofilament nylon sutures. The
proximal anastomosis was placed in an endto-side manner to the ECA using 8-0 nylon
continuous sutures. To retain patency of the

bypass graft and to eliminate turbulent flow
in the aneurysm, we then immediately
proceeded to the endovascular procedure
using a portable digital subtraction angiography instrument in the operating room.
The exposed CCA was punctured directly
and a 7F sheath ([Brite tip], Cordis, Miami,
Florida, USA) was inserted from the CCA to
the ICA (Figure 1). We injected radiopaque
dye through the 7F sheath after temporary
clipping of the cervical ICA to confirm
bypass patency and to visualize the OphA
and the aneurysmal supply by collaterals
from the ECA (Figure 2A). Then we
inserted a 7F balloon catheter ([PATLIVE],
Clinical Supply, Gifu, Japan) into the
ICA through the sheath. A microcatheter
was inserted into the aneurysm under
fluoroscopic guidance. After balloon
dilation of the ICA proximal to the
aneurysm to prevent distal embolism
(Figures 1 and 2B) we inserted a few coils
in the aneurysm to serve as anchors to

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PREVENTION OF RETROGRADE BLOOD FLOW

Figure 2. Schematic illustration of our surgical strategy. (A) After high-flow bypass, cervical internal
carotid artery (ICA) occlusion alone allows retrograde flow (arrow) into the aneurysm (AN) from the
surgically created bypass or from the ICA branches (dotted arrow) such as the ophthalmic artery
(OphA) and the meningohypophyseal trunk (MHT). (B) Coil occlusion of the aneurysmal orifice and
the ICA including the origin of the OphA and the MHT under proximal balloon protection to prevent
retrograde flow into the aneurysm. (C) The final step, ligation of the cervical ICA after the completion
of coil embolization.

prevent distal migration of coils used for
subsequent embolization. After identifying
the aneurysmal orifice, we used several
coils for tight embolization of the
aneurysmal orifice and the ICA including
the origin of the OphA and the MHT
(Figures 1 and 2). The cervical ICA was
ligated with a silk thread in all patients.
During the endovascular procedure,
3000 U of heparin were administered
intravenously, followed by 1000 U at
hourly intervals. Final external carotid
angiography was performed to confirm
bypass patency and no visualization of the
aneurysm. The total operative time ranged
from 6e8 hours.
RESULTS
A summary of our treatment outcomes is
presented in Table 1. All patients tolerated
BTO without developing neurological
deficits.
There
were
no
serious
perioperative complications. One patient
(case 2) suffered transient mild hemiparesis
and another (case 4) manifested aphasia,
but their symptoms resolved completely by
the first postoperative day. In 2 patients
postoperative diffusion-weighted imaging
showed a small high-intensity spot in the
ipsilateral cerebral hemisphere; follow-up
T2-weighted imaging detected no infarction. In case 2 we observed transient

symptom aggravation 2 weeks after surgery.
This was probably due to abrupt aneurysmal
thrombosis that resulted in the transient
expansion of the aneurysm mass seen on
magnetic resonance imaging (MRI) scans.
The preoperative symptoms gradually disappeared completely in 2 patients (cases 1
and 4) and improved in 1 (case 2). The visual
symptoms were unchanged in 2 patients
(cases 3 and 5); preoperative damage of their
cranial nerves appeared to have been severe.
The mean follow-up period was 7 years
(range, 5e12 years). The grafts remained
patent in all patients. Cerebral angiography
or magnetic resonance angiography (MRA)
confirmed aneurysm obliteration in all
patients and no de novo aneurysms
were detected. The aneurysmal mass disappeared almost completely in 4 patients
and was markedly smaller in the other
(Table 1). In all patients the coils placed in
the aneurysm looked like small residual
lesions. All had good outcomes; the
modified Rankin scale was 0 in 2 patients
and 1 in 3 patients with visual symptoms.

Illustrative Cases
Case 1. A 43-year-old woman presented
with a 2-month history of headache and
double vision. She manifested mild right
abducens nerve paresis. MRI showed a mass
lesion on the inner side of the temporal lobe

WORLD NEUROSURGERY 83 [6]: 1127-1134, JUNE 2015

(Figure 3A). Angiography revealed a giant
aneurysm at the cavernous segment of the
right ICA (Figure 3B).
We placed an ECAeM2 bypass with an
RA graft on the right side. Selective
angiography of the ECA after temporary
occlusion of the ICA showed patency of the
RA graft. The OphA and ICA were supplied
by collaterals from the ECA in the early
phase (Figure 3C). Filling of the aneurysm
lumen through the surgically created
bypass graft and the OphA was confirmed
in the late phase (Figure 3D). To cut off
the aneurysm from any retrograde blood
flow we performed coil embolization of
the aneurysmal orifice and the ICA
including the origin of the OphA and the
MHT (Figure 3E). The fundus of the
aneurysm was loosely packed with coils to
prevent distal coil migration. Angiography
confirmed no filling of the aneurysm and
patency of the bypass graft. The OphA
was fed by ECA networks (Figure 3F).
Her postoperative course was uneventful
and her preoperative symptoms subsided
gradually. Angiography of the ECA performed 7 days after the operation revealed
no filling of the aneurysm and patency of the
bypass graft (Figure 3G). On T1-weighted
images acquired 5 years after the operation
there was complete disappearance of the
aneurysmal mass. Coils placed in the
aneurysm were discernible (Figure 3H).
MRA confirmed bypass patency (Figure 3I)
and the patient continues to do well with
no neurological deficits.
Case 4. A 58-year-old woman presented
with a 6-month history of visual disturbance
in her left eye; visual acuity on the left was
markedly decreased (0.05). MRI, MRA, and
angiography showed a giant aneurysm
arising at the C2eC3 segment of the left ICA
(Figures 4AeC). Endovascular coil occlusion
of the aneurysmal orifice and the ICA
including the origin of the OphA and the
MHT and placement of a high-flow bypass
was as in case 1. Figure 4D is a preembolization angiogram. The aneurysmal
orifice and the ICA including the origin of
the OphA and the MHT were tightly
occluded with coils (Figure 4E). Subsequent
intraoperative selective angiography of the
ECA revealed a patent bypass (Figure 4F),
late filling of the OphA by ECA networks,
and no filling of the aneurysm (Figure 4G).
Her postoperative transient aphasia
resolved quickly and her visual disturbance

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1

DISCUSSION

6

8

Unchanged

Disappeared

Lt. C2eC3, paraclinoid
23
M
5

Cranial nerve signs: II, optic nerve; III, oculomotor nerve; VI, abducens nerve.
mRS, modified Rankin scale.

29

Visual loss
(II; almost blind)

None

Transient aphasia
Visual disturbance
(II)
29
Lt. C2eC3, paraclinoid
58
F
4

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improved gradually and normalized several
months after the operation. MRI and MRA
studies acquired 5 years after surgery
demonstrated complete disappearance of
the giant aneurysm and patency of the RA
graft (Figures 4H, I). Her modified Rankin
scale was 0, and her vision was normal 8
years after surgery.

Decreased (coils)
No
Patent

Disappeared
No
0

Patent

Disappeared
No
68
F
3

Lt. C3eC4, cavernous

15

Double vision
(III, VI)

None

Unchanged

12

1

Patent

Disappeared
No
62
F
2

Lt. C3eC4, cavernous

25

Double vision
(III, VI)

Transient hemiparesis

Transient worsening
improved

5

1

Patent

Disappeared
No
Patent
0
7
Disappeared
None
Double vision (VI),
headache
43
Rt. C3eC4, cavernous
43
F
1

Symptoms
Size (mm)
Side and Location
Age/Sex
Case
Number

Table 1. Characteristics of Patients at Admission and Surgical Results

Perioperative
Complications

Postoperative
Visual Symptoms

Follow-up
(years)

mRS

Filling

Mass

PREVENTION OF RETROGRADE BLOOD FLOW

Bypass
Graft

Aneurysm

NORIO NAKAJIMA ET AL.

We treated 5 patients with large or giant ICA
aneurysms at C2eC4 by dense coil occlusion of the aneurysmal orifice and the ICA
including the origin of the OphA and the
MHT to prevent retrograde flow into the
aneurysms. All patients received a high-flow
bypass. The long-term treatment outcomes
were excellent and surprisingly, 4 of 5
aneurysms almost completely disappeared.
Ligation of the cervical ICA with or without
ECeIC bypass is the classic treatment
for unclippable ICA aneurysms (11, 24).
Although ligation is easier than our endovascular approach and most aneurysms can
be expected to be thrombosed after cervical
ICA ligation, recanalization and rupture after
ECeIC bypass combined with ICA occlusion
have been documented (10, 12, 13, 15, 17).
Matsuda et al. (15) reported a patient with
an unruptured giant aneurysm of the ICA
who suffered aneurysmal rupture 34 days
after ICA occlusion and STAeMCA bypass.
This suggests that immediate complete
exclusion of aneurysms from the circulation
is preferable to proximal ICA occlusion. We
and other investigators (1, 20) posit that
postoperative recanalization and rupture are
due to retrograde filling of the aneurysm by
the bypass graft or by ICA branches in the
ECA network such as the OphA or the MHT
(Figure 2). In our case 1, intraoperative
selective angiography of the ECA obtained
after temporary occlusion of the cervical
ICA revealed late filling of the aneurysm
through the surgically created bypass and
the OphA. Therefore we performed dense
coil occlusion of the aneurysmal orifice and
the ICA including the origin of the OphA
and the MHT to eliminate retrograde flow
into the aneurysm. This cut off the blood
flow into the aneurysm and resulted in
its transformation into a blind sac and
complete thrombosis.
Surgical or endovascular trapping may
also be considered to stop the flow into ICA
aneurysms. However, distal clipping can be
difficult if there is not enough space for clip

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PREVENTION OF RETROGRADE BLOOD FLOW

Figure 3. Case 1. (A) Preoperative T1-weighted image demonstrated an intracavernous aneurysm. (B) Preoperative internal carotid
angiogram (anteroposterior view) demonstrating a giant aneurysm of the right internal carotid artery (ICA). (CeF) Selective angiography
of the external carotid artery (ECA) obtained during the operation. The pre-embolization angiogram (lateral view) obtained in the early
(C) and late phase (D) after ECA- radial artery (RA)-middle cerebral artery second portion bypass revealed patency of the bypass
(thin arrows) and filling of the aneurysmal lumen (thick arrows) and the cavernous portion of the ICA through the RA graft, and the
ophthalmic artery (OphA) (arrowheads) by the external networks. The intraoperative angiogram (E) showed loose packing of the
fundus of the aneurysm, dense coil embolization of the aneurysmal orifice, and the ICA including the origin of the OphA and the
meningohypophyseal trunk (large arrow), and the patent bypass (small arrows). Intraoperative angiography (F) obtained after coil
occlusion showed flow in the OphA (arrowheads). (G) Angiogram acquired 7 days after the operation revealed patency of the bypass
graft (arrows) and no filling of the aneurysm. (H) A T1-weighted image obtained 5 years after the operation showed complete
disappearance of the intracavernous mass. The inserted coils can be seen (arrow). (I) Magnetic resonance angiography confirmed
patency of the bypass graft (arrows).

insertion between the giant aneurysm
and ICA branches distal to the aneurysm.
Murayama et al. (16) obtained complete
endovascular occlusion of a large ICA
aneurysm and its parent artery with the
STAeMCA bypass. We, on the other hand,
first loosely embolized the aneurysms with
a few anchor coils to prevent distal coil

migration and to avoid dysfunction of
cranial nerves IIeVI due to the mass
effects exerted by tightly packed coils.
Cranial nerve dysfunction improved in 3 of
our 5 patients and no patients manifested
worse visual symptoms postoperatively.
Van Rooij and Sluzewski (22) reported
that 31 unruptured large or giant ICA

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aneurysms with cranial neuropathy were
treated with ICA occlusion and that the
symptom improvement was as good as in
our study.
Ishishita et al. (11), who routinely placed
a high-flow bypass in patients with large
or giant ICA aneurysms, reported that
their procedure was safe with excellent

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Figure 4. Case 4. (A, B) Preoperative T2-weighted image (A) and magnetic resonance angiography (MRA) (B) showed a giant aneurysm
in the chiasmal cistern. (C) Left carotid angiogram (anteroposterior view) demonstrated a giant aneurysm arising from the paraclinoid
segment of the left internal carotid artery (ICA) (C2 portion). (D) Intraoperative internal carotid angiogram (lateral view) obtained after
external carotid artery (ECA)- radial artery (RA)-middle cerebral artery second portion (M2) bypass showed filling of the ICA giant
aneurysm. (E) Note the loose packing of the aneurysm and dense packing of the aneurysmal orifice and the ICA including the origin of
the ophthalmic artery (OphA) and the meningohypophyseal trunk. (F, G) Selective angiography of the ECA performed after ECA-RA-M2
bypass and endovascular embolization in the early (F) and late phase (G). In the early phase (F, lateral view) the angiogram showed
occlusion of the aneurysm and patency of the RA graft (arrows). In the late phase (G) the OphA was supplied by ECA networks
(arrowheads). (H, I) Postoperative T2-weighted image (H) and magnetic resonance angiography (I) obtained 5 years after the operation
showed disappearance of the aneurysm and patency of the bypass graft (arrow).

long-term graft patency. Although all of our
patients were BTO-tolerant, we placed an
ECeIC bypass to prevent ischemic events
and the development of de novo aneurysms. Although BTO has been reported to
be useful for assessing the tolerance for ICA
sacrifice, even in BTO-tolerant patients, the
early ischemic rate was 2.0%e22.7% and
up to 1.9% developed late ischemic
complications (8, 14). Furthermore, de

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novo aneurysms developed on the contralateral side due to increased hemodynamic
stress after ICA occlusion without distal
revascularization (3, 4, 6). High-flow
ECeIC bypass surgery using an RA graft
can alleviate hemodynamic ischemia after
ICA occlusion and future hemodynamic
stress on the contralateral side. Our longterm follow-up revealed patency of the
bypass graft and no de novo aneurysm

formation. The high-flow bypass prevented
hemodynamic ischemic events, not only
in the perioperative period, but also in the
long-term period.
Our approach has some risks and
disadvantages. Although occlusion of the
origin of the OphA may result in retinal
ischemia and vision worsening, it usually
does not elicit visual disturbances because
the blood supply from the collaterals of the

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ECA is sufficient and the central retinal
artery originates from the OphA after
passing through the optic canal (7, 19).
Ocular ischemia due to thromboembolism
is more detrimental to visual acuity than
occlusion of the OphA origin. Intraoperative angiography showed blood flow
in the OphA through these collaterals and
none of our patients suffered postoperative
vision aggravation. In fact, preoperative visual disturbances were markedly improved
in 2 patients although visual loss cannot be
rule out after occlusion of the OphA.
Occlusion tests of the origin of the OphA
and the visual-evoked potentials are useful
for the selection of treatment strategies to
preserve vision (2, 18).
Distal embolism may arise if aneurysmal thrombosis occurs abruptly in the
acute postoperative phase. In fact, 2 of our
patients suffered transient postoperative
hemiparesis and aphasia. Their symptoms
subsequently resolved completely and no
cerebral infarcts were observed despite the
presence of small high-intensity spots on
postoperative diffusion-weighted imaging
studies. Appropriate intraoperative anticoagulation and postoperative antiplatelet
therapy should be considered to prevent
embolic complications in the perioperative
period. Abrupt aneurysmal thrombosis
may also produce a temporary increase
in the size of the aneurysm. One of our
patients (case 2) manifested transient
oculomotor palsy 2 weeks after surgery. It
subsided gradually in the course of aneurysmal shrinkage.
The International Study of Unruptured
Intracranial Aneurysms (ISUIA) reported
that the clipping of large or giant ICA
aneurysms resulted in a major morbidity
rate of more than 20% (23). Although our
study population was small, we achieved
aneurysm obliteration and graft patency in
all 5 patients, none of whom manifested
permanent neurological complications in
the course of long-term follow-up.
CONCLUSIONS
With meticulous attention to the surgical
techniques, retrograde flow into the aneurysm can be prevented by coil embolization
and the placement of a high-flow bypass.
We suggest that our technique is a safe and
effective treatment in patients with large or
giant ICA aneurysms. The endovascular

PREVENTION OF RETROGRADE BLOOD FLOW

technique and the placement of a high-flow
bypass involve fewer surgical manipulations for completing aneurysmal occlusion.
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Conflict of interest statement: The authors declare that the
article content was composed in the absence of any
commercial or financial relationships that could be construed
as a potential conflict of interest.
N. Nakajima and S. Nagahiro contributed equally to the
project.

Received 30 July 2014; accepted 19 January 2015;
published online 11 February 2015
Citation: World Neurosurg. (2015) 83, 6:1127-1134.
http://dx.doi.org/10.1016/j.wneu.2015.01.037
Journal homepage: www.WORLDNEUROSURGERY.org
Available online: www.sciencedirect.com
ª 2015 The Authors. Published by Elsevier Inc. This is an
open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/)

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