This study describes the experiences of 24 patients treated for complex middle cerebral artery (MCA) aneurysms using bypass surgery combined with parent vessel occlusion. The aneurysms ranged in size from 7-60mm, with most being giant or fusiform. Bypass surgeries included extracranial-intracranial and intracranial-intracranial bypass procedures. Parent vessel occlusion involved partial or total trapping, with or without aneurysm resection. Outcomes were generally good, with 100% aneurysm obliteration and 21 patients (88%) having good functional outcomes, though permanent deficits occurred in 5 patients, most associated with M1 aneurysms. Location of the aneurysm was an important factor in planning treatment

1. J Neurosurg 120:398–408, 2014
398 J Neurosurg / Volume 120 / February 2014
©AANS, 2014
T
he treatment of giant (diameter ≥ 2.5 cm) or fu-
siform middle cerebral artery (MCA) aneurysms
may be very challenging despite the introduction
of refined microsurgical techniques and advances in endo-
vascular methods.3,8–11,14,15,17,22,26,27,33,40
Giant saccular aneurysms may have wide and par-
tially calcified necks, with major branches or perforating
arteries incorporated at the base, or the aneurysm walls
may be atherosclerotic and the lumen partially throm-
bosed, making clipping or endovascular embolization
challenging and often almost impossible. Fusiform an-
eurysms have no neck at all, as the entire vessel wall of
the dilated arterial segment is pathological, and the lumen
may be partially thrombosed, making these lesions also
unamenable to conventional treatment techniques. Fusi-
form aneurysms of the M1 segment of the MCA typically
involve origins of lenticulostriate arteries, further compli-
cating treatment strategies. Lastly, failure of previous en-
dovascular treatment may present challenging problems.
Bypass surgery for complex middle cerebral artery
aneurysms: impact of the exact location in the MCA tree
Clinical article
Leena Kivipelto, M.D., Ph.D.,1
Mika Niemelä, M.D., Ph.D.,1
Torstein Meling, M.D., Ph.D.,2
Martin Lehecka, M.D., Ph.D.,1
Hanna Lehto, M.D.,1
and Juha Hernesniemi, M.D., Ph.D.1
1
Department of Neurosurgery, Helsinki University Hospital, Helsinki, Finland; and 2
Department of
Neurosurgery, Oslo University Hospital-Rikshospitalet, Oslo, Norway
Object. The object of this study was to describe the authors’ institutional experience in the treatment of complex
middle cerebral artery (MCA) aneurysms necessitating bypass and vessel sacrifice.
Methods. Cases in which patients with MCA aneurysms were treated with a combination of bypass and parent
artery sacrifice were reviewed retrospectively.
Results. The authors identified 24 patients (mean age 46 years) who were treated with bypass and parent artery
sacrifice. The aneurysms were located in the M1 segment in 7 patients, MCA bifurcation in 8, and more distally in 9.
The mean aneurysm diameter was 30 mm (range 7–60 mm, median 26 mm). There were 8 saccular and 16 fusiform
aneurysms.
Twenty-one extracranial-intracranial and 4 intracranial-intracranial bypasses were performed. Partial or total
trapping (only) of the parent artery was performed in 17 cases, trapping with resection of aneurysm in 3, and aneu-
rysm clipping with sacrifice of an M2 branch in 4.
The mean follow-up period was 27 months. The aneurysm obliteration rate was 100%. No recanalization of the
aneurysms was detected during follow-up.
There was 1 perioperative death (4% mortality rate) and 6 cerebrovascular accidents, causing permanent mor-
bidity in 5 patients. The median modified Rankin Scale score of patients with an M1 aneurysm increased from 0 pre-
operatively to 2 at latest follow-up, while the score was unchanged in other patients. Most of the permanent deficits
were associated with M1 aneurysms. Twenty-one patients (88%) had good outcome as defined by a Glasgow Outcome
Scale score of 4 or 5.
Conclusions. Bypass in combination with parent vessel occlusion is a useful technique with acceptable frequen-
cies of morbidity and mortality for complex MCA aneurysms when conventional surgical or endovascular techniques
are not feasible. The location of the aneurysm should be considered when planning the type of bypass and the site of
vessel occlusion. Flow alteration by partial trapping may be preferable to total trapping for the M1 aneurysms.
(http://thejns.org/doi/abs/10.3171/2013.10.JNS13738)
Key Words • cerebral revascularization • giant aneurysm •
fusiform aneurysm • aneurysm treatment • parent vessel occlusion •
vascular disorders
Abbreviations used in this paper: ASA = acetylsalicylic acid;
CTA = CT angiography; DS = digital subtraction; DSA = DS
angiography; ECA = external carotid artery; EC-IC = extracranial-
intracranial; ELANA = excimer laser-assisted nonocclusive anas-
tomosis; GOS = Glasgow Outcome Scale; ICA = internal carotid
artery; IC-IC = intracranial-intracranial; MCA = middle cerebral
artery; mRS = modified Rankin Scale; OA = occipital artery; SAH =
subarachnoid hemorrhage; STA = superficial temporal artery.

2. J Neurosurg / Volume 120 / February 2014
Bypass and vessel occlusion for complex MCA aneurysms
399
Nevertheless, because untreated giant aneurysms have a
5-year combined morbidity and mortality rate of 80%, it is
widely agreed that they should not be left untreated.4,12,39,48
When conventional surgical or endovascular treat-
ment is not feasible, occlusion of the aneurysm may be
achieved by parent vessel sacrifice combined with distal
revascularization. Several modifications of this treatment
modality have been described, including extracranial-
intracranial (EC-IC) or intracranial-intracranial (IC-IC)
bypass or more refined revascularization methods, such
as in situ bypass or various vascular reconstructions, in
combination with total or partial trapping of the aneurysm
by means of parent artery occlusion.21,23,24,31,34,36–38,46
So far, only small series of MCA aneurysms treated
with a combination of bypass and parent vessel sacrifice
have been described. We report our experience in 24 com-
plex MCA aneurysm cases treated with an EC-IC or IC-IC
bypass followed by partial or complete parent vessel oc-
clusion. We also discuss the different treatment require-
ments for aneurysms at different locations of the MCA
vasculature.
Methods
The Helsinki intracranial aneurysm database was
screened to identify all patients with an MCA aneurysm
treated with a combination of bypass and parent vessel oc-
clusion (Table 1). The database includes over 10,000 cases
involving patients with intracranial aneurysms admitted
to the Department of Neurosurgery at Helsinki Univer-
sity Hospital since 1937. Medical records were reviewed
for relevant clinical information. The study was approved
by the Ethics Committee of Helsinki University Central
Hospital.
Patients
Twenty-four patients (15 men and 9 women) were
treated for complex MCA aneurysms using a combina-
tion of bypass and vessel sacrifice between January 1998
(when bypass surgery was initiated at our institution) and
June 2012. The mean age of the patients was 46.5 years
(range 12–73 years, median 48 years) (Tables 1 and 2).
During the time period of our present study, 3780 patients
with intracranial aneurysms were treated at our institu-
tion, and 48% of these patients harbored MCA aneurysms,
including 45 giant MCA aneurysms. Thus, the 24 MCA
aneurysms treated with bypass represent about 1% of all
the MCA aneurysms surgically treated at our institution.
In addition to these 24 cases, there were 4 cases in
which a bypass was planned and attempted but was not
successfully completed. The aneurysm was then directly
clipped in the same surgery or later. A summary of these
cases is presented in Table 3, but these cases were exclud-
ed from further analysis of the bypass cases.
Aneurysms
The aneurysms were deemed “complex” on the ba-
sis of preoperative imaging or previous surgical explora-
tion. The size, morphology, and location of aneurysms
were assessed by digital subtraction angiography (DSA)
combined with CT, 3D CT angiography (CTA), or MRI.
We reviewed the size and presence of intraaneurysmal
thrombus; the morphological characteristics, side, and lo-
cation of the aneurysm; symptoms at presentation; previ-
ous treatment procedures; and the presence of other an-
eurysms (Tables 1 and 2). Aneurysm size was measured
as the largest outer diameter for saccular aneurysms and
as the length of the affected arterial segment for fusiform
aneurysms.
The size of the 24 aneurysms ranged from 7 to 60
mm (mean 30, median 26). Fifteen patients had a giant
aneurysm. Six of the aneurysms were larger than 4 cm
and were causing mass effect. In 17 cases (71%), the aneu-
rysms were partially thrombosed. There were 16 fusiform
and 8 saccular aneurysms, as defined by their angiograph-
ic morphology. Eleven aneurysms were on the right side,
13 on the left. The aneurysms were located in the M1 seg-
ment in 7 patients, at the MCA bifurcation in 8, and more
distally in 9. All M1 segment and distal MCA aneurysms
TABLE 1: Baseline characteristics in 24 patients*
Description Value
sex
male 15 (63)
female 9 (37)
age (yrs)
mean 46.5
range 12–73
presenting symptom
SAH 2 (8)
seizure 10 (42)
mass effect 3 (12)
TIA 4 (17)
none (incidental finding) 5 (21)
aneurysm location
left side 13 (54)
right side 11 (46)
M1 segment 7 (29)
bifurcation 8 (33)
distal 9 (38)
aneurysm characteristics
saccular 8 (33)
fusiform 16 (67)
partially thrombosed 17 (71)
aneurysm size
<20 mm 3 (12)
20–24 mm 6 (25)
25–39 mm 9 (38)
≥40 mm 6 (25)
previous aneurysm treatment attempts
wrapping 1 (4)
surgical exploration 2 (8)
diverter stenting 1 (4)
* Values represent number of patients or aneurysms (%) unless other-
wise indicated. TIA = transient ischemic attack.

3. L. Kivipelto et al.
400 J Neurosurg / Volume 120 / February 2014
TABLE2:ClinicalsummaryofpatientsundergoingacombinationofbypassandvesselocclusionforcomplexMCAaneurysms*
Case
No.
Age
(yrs),
Sex
MCA
SegSide
Aneur
Morph
Aneur
Size
(mm)
Intralum
ThrombPrevTxBypassTypeAneurTx
Bypass
Patent
PostopAdd’lProcsStroke
FU
(mos)
mRSScore
GOS
Score
Aneur
Oblit
Bypass
Patent
atFUPreopFU
121,MM1rtfusif20−STA-MCA×2distaloccl++12024++
268,FM1rtfusif22−wrappingECA-MCAbif,
ELANA
proxoccl++12024+NA
347,MM1ltfusif25−ICA-M1,ELANAproxoccl+−76005+NA
436,MM1ltfusif26+STA-MCAdistaloccl+−13115+NA
548,MM1rtfusif40+STA-M2proxoccl(endovasc)++5024+NA
6†52,MM1ltfusif50+flowdiverterSTA-MCAdistaloccl+evacofpostophema-
toma;aneurre-
section
−1.5461++
773,MM1ltfusif60+STA-MCAresection++4133+NA
848,Mbifltsacc 7+surgexplo-
ration
STA-MCAclipping&M2sacri-
fice
+−45114+−
948,Mbifrtsacc20−STA-MCAclipping&M2sacri-
fice
+−36015+−
1040,Mbifrtsacc23+STA-MCAclipping&M2sacri-
fice
+−24005++
1150,Mbifltsacc30+ICA-M2,ELANA;
STA-MCA
distaloccl;distal
occl
+−26005+−
1245,Fbifrtsacc30+STA-MCA×2proxoccl+−57115++
1322,Mbifrtsacc34+STA-MCA×2trapping+−53115++
1445,Mbifrtsacc35+ICA-M2,ELANAclipping&M2sacri-
fice
+VPshuntforHC−7105+NA
1537,Fbifrtsacc55+STA-MCAdistaloccl(oneM2
prev’lythrom-
bosedspont)
+−17114+−
1639,Mdistalrtfusif10−STA-MCAresection+−76105+NA
1755,Mdistalrtfusif10−STA-MCAproxoccl+−32005++
1863,Fdistalltfusif20+STA-MCAtrapping−−2115+−
1952,Fdistalltfusif21+OA-MCAdistaloccl+−52234+−
2012,Fdistalltfusif25−STA-MCAproxoccl+−28014++
2159,Fdistalltfusif25+STA-MCAdistaloccl+−2005++
2261,Fdistalltfusif35+surgexplo-
ration
STA-MCAtrapping+−31105++
2324,Mdistalltfusif40+ICA-M2,ELANAdistaloccl−aneurresection+12005+NA
2467,Fdistalltfusif50+STA-MCA×2resection++6033++
* Add’l=additional;aneur=aneurysm;bif=bifurcation;endovasc=endovascular;evac=evacuation;FU=follow-up;fusif=fusiform;HC=hydrocephalus;intralum=intraluminal;morph=morphol-
ogy;NA=notapplicable;oblit=obliteration;occl=occlusion;prev=previous;prev’ly=previously;procs=procedures;prox=proximal;sacc=saccular;seg=segment;spont=spontaneously;surg
=surgical;thromb=thrombus;Tx=treatment;VP=ventriculoperitoneal;+=yes;−=no.
† Thispatientdied6weeksaftersurgery,buthisbypasswasopenandtheaneurysmwasoccludedatthetimeofhisdeath.(SeeClinicalOutcomesectionfordetails.)

4. J Neurosurg / Volume 120 / February 2014
Bypass and vessel occlusion for complex MCA aneurysms
401
were fusiform, whereas all bifurcation aneurysms were
saccular.
Two patients (Cases 3 and 16) presented initially with
subarachnoid hemorrhage (SAH). Ten patients had epilep-
tic seizures, 3 had symptoms of mass effect, and 4 had is-
chemic symptoms; 5 aneurysms were incidental findings.
One patient who presented with SAH (Case 16; Hunt and
Hess Grade II, Fisher Grade 3) was treated on an emer-
gency basis. Another patient whose condition was dete-
riorating rapidly (Case 6) due to perianeurysmal bleeding
and increasing mass affect from a giant MCA aneurysm
was admitted and surgically treated urgently.
Two aneurysms had been surgically explored earlier
and deemed unclippable (Cases 8 and 22). In 1 case (Case
2), the fusiform M1 aneurysm continued to grow despite
being wrapped with cotton 7 years earlier as did another
M1 fusiform giant aneurysm after flow diverter insertion
5 months before the bypass and vessel sacrifice procedure
(Case 6). Four patients had multiple aneurysms: at the
anterior communicating artery (Case 2), at the origin of
the posterior inferior cerebellar artery (Case 8), and in the
contralateral MCA (Cases 10 and 21). (The treatment of
these additional aneurysms is not included in this paper.)
Surgical Strategy
Bypass type, aneurysm treatment procedures, graft
patency, aneurysm obliteration, postoperative complica-
tions, and clinical outcome (mRS and GOS scores) were
assessed by reviewing the imaging studies, radiology re-
ports, clinical examination results, and in- and outpatient
records.
The preliminary planning of surgical strategy—by-
pass type and whether a proximal or distal parent vessel
occlusion would be performed—was done preoperatively
based on the angiographic findings. No preoperative flow
measurements were performed. During surgery, after ex-
ploration of the aneurysm and associated vessels, the de-
tails of the surgical plan were confirmed or further modi-
fied, if necessary. We did not perform electrophysiological
monitoring of the patients during surgery.
Decisions about bypass type depended on the caliber
of the superficial temporal artery (STA) and the location
of the planned vessel occlusion (the expected flow de-
mand). The estimation of the STA caliber was a subjec-
tive visual assessment based on the preoperative DSA and
CTA studies, confirmed by the cut flow measurements in-
traoperatively. In most cases we preferred an STA-MCA
bypass, if possible. For some aneurysms we performed an
EC-IC or IC-IC bypass with the excimer laser–assisted
nonocclusive anastomosis (ELANA) method with saphe-
nous vein graft. Both the conventional STA-MCA6,29,49
and
the ELANA bypass technique42–44
have been comprehen-
sively described previously.
In the planning of the treatment protocol, the follow-
ing principles were considered.
M1 Aneurysms. The flow deficit caused by M1 oc-
clusion can be well replaced with an appropriate bypass
distally, but complete trapping of an M1 aneurysmal seg-
ment would occlude the lenticulostriate perforator orifices
leading to basal ganglion infarction and permanent neuro-
TABLE3:ClinicalsummaryofpatientstreatedforacomplexMCAaneurysmwithouttheaidofbypassduetointraoperativebypassfailure*
Age
(yrs),
Sex
Aneur
Loc
Aneur
Morph
Aneur
Size
(mm)
Intralum
ThrombPres
Prev
Tx
Bypass
TypePossReasonsforBypassFailureAneurTxStroke
Preop
mRS
FU
mRSGOS
Aneur
Oblit
FU
(mos)
54,FrtM1fusif60+masseffect−ECA-M2emergop;thrombosisatproxanast,
despitesev’lrevs
1)thrombect,clipping;2)de-
comprcraniectDay2
+424+19
51,Mltbifsacc30+SAHcoiling×3ICA-M2,
ELANA
occlofdistal(ELANA)anastdespite
repeatedrevs;sizediscrepbtwn
saphveingraft&MCAbranch?
thrombect,clippingDay3+033+19
61,Fltdistalfusif60+SzSTA-MCA
bypass
atother
hosp
ECA-M2,
ELANA
occlofdistal(ELANA)anastdespite
repeatedrevs;sizediscrepbtwn
saphveingraft&MCAbranch?
thrombect,clippingDay6−024− 4
42,Frtdistalfusif 3−acuteSAH
+ICH;
HH5,F4
−STA-MCAemergop;brainedemaduetosevere
SAH,diffconditions&techprobs
throughoutop
1)trapping,ICHevac;2)de-
comprcraniect,ICHre-
evacDay2
+543+41
* Anast=anastomosis;craniect=craniectomy;decompr=decompressive;diff=difficult;discrep=discrepancy;emerg=emergency;F=Fishergrade;FU=follow-up;HH=HuntandHessgrade;
hosp=hospital;ICH=intracerebralhematoma;loc=location;poss=possible;pres=presentation;probs=problems;re-evac=re-evacuation;revs=revisions;saph=saphenous;sev’l=several;Sz
=seizure;tech=technical;thrombect=thrombectomy.

5. L. Kivipelto et al.
402 J Neurosurg / Volume 120 / February 2014
logical deficits. By occluding the M1 segment either proxi-
mally or distally to the aneurysm, a flow alteration can
be induced leading to aneurysm thrombosis with a flow
channel to the perforating branches remaining.
MCA Bifurcation Aneurysms. These lesions can be
treated by clipping the neck together with one of the M2
branches, protected with a bypass, while preserving the
anterograde flow to the other M2 trunk, or by revascular-
izing both M2 branches followed by proximal (distal M1
occlusion) or distal occlusion (both M2 branches distal to
aneurysm). Trapping is also an option if no perforators
originate at the bifurcation.
Distal MCA Aneurysms. For distal MCA aneurysms,
distal revascularization followed by either proximal or
distal parent artery occlusion will result in aneurysm
thrombosis. Trapping is also possible, since no significant
perforating branches usually originate from these distal
segments.
Drug Treatment and Anesthesia
Preoperatively, patients were treated with antiplatelet
therapy (acetylsalicylic acid [ASA] 100 mg daily), and the
medication was continued after surgery. If for some rea-
son ASA therapy had not been started before surgery, 300
mg ASA was administered intravenously during surgery.
Systemic heparin was not routinely used, but the surgi-
cal field was generously flushed with heparinized saline
throughout the surgery. Bypass procedures were per-
formed under general anesthesia, following the principles
of neuroanesthesia described in detail by Randell et al.32
Assessment of Bypass Patency and Aneurysm Occlusion
Intraoperatively, the patency of the bypass was as-
sessed using direct blood flow measurement with an ul-
trasonic flow probe (Charbel Micro-Flowprobe, Transonic
Systems Inc.), DSA, indocyanine green video angiogra-
phy, or a combination of these methods. Following com-
pletion of the bypass, partial or total trapping of the parent
artery or trapping followed by resection of the aneurysm
was performed. DSA was performed in all patients be-
tween the 1st and 3rd postoperative day. Aneurysm oblit-
eration was regarded as complete if there was no residual
contrast filling of the aneurysm.
Results
The details of surgical procedures performed are
summarized in Tables 2 and 4.
Bypass Type and Treatment of the Aneurysm
Twenty-one EC-IC and 4 IC-IC bypasses were per-
formed. The STA was used as donor in 19 cases, and the
occipital artery (OA), in 1 case. The external carotid ar-
tery (ECA, in 1 case) or intracranial internal carotid ar-
tery (ICA, in 4 cases) served as donor with a saphenous
vein graft used as a conduit in the 5 ELANA bypasses.
The bypass procedure was followed by parent artery
partial occlusion in 14 cases: proximal occlusion in 6 pa-
tients, distal occlusion in 8 patients (in 1 case the proximal
occlusion was performed endovascularly on the 1st post-
operative day, all others were intraoperative clip occlu-
sions); trapping in 3 patients; trapping with aneurysm re-
section in another 3 patients. Four bifurcation aneurysms
were clipped together with an incorporated M2 branch.
Two aneurysms, initially treated with distal occlusion,
were trapped and resected in a second surgery (see Surgi-
cal Outcome).
All M1 aneurysms were fusiform. Six EC-IC bypasses
(5 STA-MCA, 1 ECA-MCA ELANA) and 1 IC-IC bypass
(ICA-MCA ELANA) were constructed, followed by prox-
imal occlusion in 3 patients and distal occlusion in another
3. One M1 aneurysm was trapped and resected.
All MCA bifurcation aneurysms were classified as
saccular. Seven STA-MCA bypasses and 2 IC-IC bypass-
es (ICA-MCA ELANA) were performed. Four aneurysms
were clipped with sacrifice of one of the M2 branches (first
revascularized with a bypass). Proximal occlusion was
performed in 1 patient, distal occlusion in 2 patients, and
trapping in 1 patient. One of the patients (Case 11) was
operated on twice for a giant saccular bifurcation aneu-
rysm: an IC-IC bypass was made followed by distal oc-
clusion of the dominant M2 branch and the flow alteration
TABLE 4: Treatment characteristics and aneurysm location*
Aneurysm
Location
Variable Total (%) M1 Bif Distal
bypass characteristics
all bypasses 25 (100) 7 9 9
conventional 20 (80) 5 7 8
ELANA 5 (20) 2 2 1
EC-IC 21 (84) 6 7 8
STA-MCA 19 (76) 5 7 7
OA-MCA 1 (4) 1
ECA-MCA (ELANA) 1 (4) 1
IC-IC 4 (16) 1 2 1
ICA-MCA (ELANA) 4 (16) 1 2 1
bypass recipient artery
M1 1 (4) 1
MCA bifurcation 1 (4) 1
M2 4 (16) 1 2 1
M3–M4 19 (76) 4 7 8
aneurysm treatment (24 aneurysms)
partial trapping 14 (58) 6 3 5
proximal occlusion 6 (25) 3 1 2
distal occlusion 8 (33)* 3* 2 3*
total trapping 6 (25) 1 1 4
trapping only 3 (12.5) 1 2
trapping & resection 3 (12.5) 1 2
clipping, selective sacrifice of 1 M2 4 (17) 4
* Two aneurysms (1 M1 and 1 distal MCA segment aneurysm) were
primarily treated with distal parent vessel occlusion (included in the
numbers in this table) but later were trapped and resected in a second
surgery. See text for details.

6. J Neurosurg / Volume 120 / February 2014
Bypass and vessel occlusion for complex MCA aneurysms
403
was expected to induce a gradual aneurysm thrombosis.
However, as no signs of progressive aneurysm obliteration
were detected, an STA-MCA bypass to the nondominant
M2 region was performed 11 days later and the branch was
occluded distal to the aneurysm.
Distal Aneurysms. All aneurysms distal to the bifur-
cation were morphologically fusiform. They were treated
with 8 EC-IC bypasses (7 STA-MCA, 1 OA-MCA) and 1
IC-IC bypass (ICA-MCA ELANA), followed by proximal
occlusion in 2 patients, distal occlusion in 3, trapping in 2,
and trapping and resection in another 2 patients.
Surgical Outcome
At the end of surgery, the bypass was patent in all
patients (Table 2).
In 2 patients with distal MCA aneurysms (Cases 18
and 23), a bypass occlusion was detected angiographically
on the 1st postoperative day (early bypass patency rate
92%).
Postoperatively, 23 aneurysms (96%) were completely
obliterated. A bypass for a giant fusiform M2 aneurysm
(Case 23) became thrombosed on the 1st postoperative
day, and brisk residual filling of the aneurysm was detect-
ed. The patient underwent a second surgery, with trapping
and resection of the aneurysm, 3 days later.
One patient (Case 6) underwent a second operation
for evacuation of Sylvian fissure hematoma and resection
of the giant aneurysm to relieve mass effect and deterio-
rating clinical condition.
No perioperative aneurysm ruptures were encoun-
tered.
During follow-up (mean 27 months, range 1.5–76
months, median 24 months) no sign of aneurysm recanali-
zation was detected. The patency of the bypasses was not
systematically assessed in long-term follow-up if no new
ischemic symptoms occurred.
Clinical Outcome
One patient died 6 weeks after surgery (the patient in
Case 6, who had a 5-cm M1 aneurysm and surrounding
edema, with a preoperative mRS score of 4; Table 2), with
severe brain edema and hemorrhage leading to herniation
and death. His bypass was open and the aneurysm was
occluded at the time of death.
Six patients (25%) had new neurological deficits, with
ischemic lesions seen on postoperative CT scans. One of
these patients recovered fully, but 5 (21%) had permanent
symptoms (mild to moderate hemiparesis and dysphasia);
3 of the 5 patients remained independent. Vasospasm did
not occur. Six postoperative hematomas (2 subdural, 4
intracerebral) were detected on routine postoperative CT
scans, but only one needed evacuation. One patient with
hydrocephalus needed a shunt. Two patients in whom both
STA branches were used for bypass developed skin necro-
sis around the surgical wound edges; one recovered with
conservative treatment, one required skin grafting. Five
patients had postoperative meningitis, 6 had pneumonia,
and 1 had a deep venous thrombosis and pulmonary em-
bolism.
The mean follow-up period was 27 months (range
1.5–76 months, median 24 months). The median mRS
score for all patients was 0 preoperatively and 1 at the
latest follow-up. The preoperative median mRS scores for
M1, bifurcation, and distal MCA aneurysms were 0, 1, and
0, respectively. The postoperative median mRS scores for
M1, bifurcation, and distal MCA aneurysms were 2, 1, and
0, respectively. A good outcome (GOS score 5 or 4) was
seen in 21 (88%) of 24 patients. Functional outcomes are
summarized in Tables 2 and 5.
Illustrative Cases
Case 3 (M1 Aneurysm)
A 47-year-old man presented to another hospital with
an SAH 7 months before presenting to our institution. A
fusiform aneurysm of the left M1 segment was found (Fig.
1 left), and the patient was subsequently referred to our
hospital for consultation and treatment. The aneurysm was
considered unclippable on the basis of the angiographic
findings, and we estimated that a relatively high flow was
needed to revascularize the entire MCA territory, with the
revascularization to be followed by proximal or distal oc-
clusion of the parent artery. A saphenous vein graft was
harvested, and a left pterional craniotomy was performed
and the sylvian fissure dissected. The large aneurysm and
the M1—both distally and proximally to the fusiform an-
eurysmal segment—were exposed. A platinum ring used
in the ELANA technique was sutured onto the distal ICA
together with a vein graft, and another ring and vein graft
were sutured onto the distal M1. The laser arteriotomies
were performed, and the proximal and distal sections of
the vein graft were sutured in an end-to-end anastomosis.
Because we had good access to the proximal end of the
aneurysm, a proximal clip occlusion of the M1 adjacent to
the origin of the fusiform segment was performed so that
the retrograde flow from the bypass would maintain the
patency of the perforating arteries originating from the
aneurysmal segment. Postoperatively, the patient had tran-
sient mild dysphasia, which resolved within a few days.
Postoperative DSA demonstrated good blood flow in the
bypass and distal MCA branches, with no filling of the
aneurysm (Fig. 1 right).
Case 13 (MCA Bifurcation Aneurysm)
A 22-year-old man had a motor vehicle accident, sus-
pected to be due to an epileptic seizure. On CT, CTA, and
DSA (Fig. 2 left), a giant (outer diameter 35 mm) wide-
necked and partially thrombosed (23 mm diameter of
the filling part) aneurysm of the right MCA bifurcation
was found, with the frontal and temporal M2 branches
originating from the aneurysm sac. As both branches of
the STA were robust, a double STA-MCA bypass was
planned. The aneurysm and the M2 branches were ex-
plored via a pterional craniotomy. By following the MCA
branches, suitable M3/M4 arteries distal to the aneurysm
were chosen from each M2 vascular tree as recipient sites.
Two STA-MCA bypasses were constructed. As the short
M1 segment was accessible, the aneurysm was trapped by
clipping the M1 proximally to the aneurysm and both M2
segments as they exited the aneurysm wall. Excellent flow
in the bypasses was detected with Flowmeter (Charbel

7. L. Kivipelto et al.
404 J Neurosurg / Volume 120 / February 2014
Micro-Flowprobe, Transonic Systems Inc.): 25 ml/min
before and 50 ml/min after trapping of the aneurysm from
each STA conduit. On postoperative imaging, the MCA
branches filled through the bypasses, and there was no
filling of the aneurysm (Fig. 2 right). The patient remained
neurologically intact.
Case 20 (Distal MCA Aneurysm)
A 12-year-old girl was examined because of intense
headaches, and a fusiform left temporal M3 aneurysm
with a diameter of 25 mm was identified (Fig. 3 A and B).
An STA-MCA bypass combined with trapping or proxi-
mal/distal parent artery occlusion was planned. After
preparation of the robust frontal STA branch, a relatively
large pterional craniotomy was performed, and the syl-
vian fissure was opened. As the aneurysm was explored,
branches originating from the side of the fusiform seg-
ment not detected on DSA were identified, indicating that
trapping would lead to infarction. The arteries distal to
the aneurysm were located so far posteriorly that the cra-
niotomy had to be extended to expose these distal vessels,
one of which was selected as the STA-MCA bypass re-
cipient. After completion of the end-to-side anastomosis,
the parent M3 arterial segment was clipped immediately
proximal to the fusiform segment. The flow of the bypass
was 7 ml/min before the proximal occlusion of the M3
branch and 24 ml/min after occlusion. On the 4th postop-
erative day the patient developed focal epileptic symptoms
and antiepileptic medication was started. On postopera-
tive CTA, the arteries distal to the aneurysm were filling
through a patent bypass and no filling of the aneurysm
was detected (Fig. 3C).
Discussion
This is the first study to report on the treatment strate-
gies and treatment results for a series of complex MCA
aneurysms requiring bypass surgery with an emphasis on
the exact location (M1, bifurcation, and distal) of the an-
eurysm. Complex MCA aneurysms that cannot be treated
with conventional surgical techniques are very rare, espe-
cially in high-volume centers like ours where microsurgi-
cal experience is at a high level. These lesions represented
only 1% of all MCA aneurysms treated at our institution.
Our series of 24 cases in which patients were treated with
the combination of bypass and parent vessel occlusion for
MCA aneurysms is to our knowledge the largest such se-
ries published. Our results, with a 4% mortality rate and
a 21% permanent morbidity rate, compare well with those
of previously reported smaller series. Complete aneurysm
obliteration was achieved in all cases and good clinical
outcome (GOS score 4 or 5) in close to 90% of the pa-
tients.
In the earlier publications, including 5 or more cases
of complex MCA aneurysms treated with the combina-
tion of bypass and vessel occlusion, the treatment-related
mortality rates vary from 0% to 11% and morbidity from
4.9% to 50%2,19,23,31,34,36–38,46
(Table 6).
Kalani et al.23
published a series of 16 giant MCA an-
eurysms treated with EC-IC bypass and vessel occlusion.
A 75% aneurysm obliteration rate was achieved, with 0%
mortality and 31% morbidity and excellent or good clini-
cal outcome in 94% of cases. Seo et al.37
reported a 100%
aneurysm obliteration rate in a series of 9 complex MCA
aneurysms after revascularization followed by excision,
clipping, or trapping of the aneurysm; there was an 11%
mortality rate and 22% morbidity rate, with 67% rate of
favorable clinical outcome. Twenty-two MCA aneurysms
were treated with ELANA bypass by van Doormaal et
al.46
with 5% perioperative mortality, 36% morbidity, and
77% favorable outcome. The complete aneurysm oblit-
eration rate was not reported clearly. Sekhar et al.36
pub-
lished a series of 7 complex MCA aneurysm cases with
different reconstructive solutions, including direct branch
reimplantation and various arterial interposition grafts,
with excellent results (100% aneurysm obliteration rate,
no mortality, 14% morbidity). Similar reconstructive tech-
niques and IC-IC bypasses were described in a few larger
series of cases of various complex cerebral aneurysms,
including treatment of 9,2
5,31
and 1634
MCA aneurysms.
A variety of surgical and endovascular techniques and
combinations of these modalities were applied to treat 48
complex intracranial aneurysms, among them 7 MCA an-
eurysms treated with the aid of bypass.19
Treatment Principles
Although clipping or thrombectomy combined with
clip reconstruction is usually the firstline treatment for
TABLE 5: Functional outcome for patients with complex MCA
aneurysm treated with bypass–vessel occlusion technique
Aneurysm Location
Preop
Median mRS
Median mRS
at FU Median GOS
all aneurysms 0 1 5
M1 segment 0 2 4
bifurcation 1 1 5
distal segments 0 0 5
Fig. 1. Case 3. Preoperative (left) and postoperative (right) antero-
posterior DS angiograms. Digital subtraction angiography demonstrat-
ed a giant fusiform aneurysm in the M1 segment of the left MCA in this
47-year-old man (left). An ELANA bypass from the ICA to the distal M1
with an interpositioned saphenous vein graft, followed by proximal clip
occlusion of the M1 was performed. The postoperative angiogram (right)
shows brisk anterograde filling of the distal MCA branches through the
patent bypass and obliteration of the aneurysm.

8. J Neurosurg / Volume 120 / February 2014
Bypass and vessel occlusion for complex MCA aneurysms
405
saccular MCA aneurysms,33
when applied to giant par-
tially thrombosed aneurysms these methods do carry in-
trinsic risks of arterial occlusion with ischemic sequelae.
Giant fusiform aneurysms typically have a longitudinal
or serpentine flow channel inside the thrombus,25
and the
fusiform pathological segment often involves the entire
circumference of the vessel wall, making these lesions
unclippable. Wrapping of the aneurysm with cotton or
other materials has been used as an alternative treatment
for “unclippable” aneurysms, but this method is not con-
sidered durable.7,13
The DeBakey vascular clamp–assisted
clipping of giant aneurysms with a partially calcified ath-
eromatic base has been described,28
and this method can
facilitate direct clipping in some rare cases. If previously
performed coil embolization or stent placement has failed,
clipping may be impossible with the endovascular mate-
rial inside the vessel or aneurysm lumen.
In the bypass-aided method, a bypass is first con-
structed to feed the vascular tree beyond the aneurysm;
this is followed by a selected procedure to obliterate the
aneurysm itself. Trapping of the aneurysm will give an
immediate and definitive result by completely isolating
the aneurysm from the circulation. Occluding the parent
artery proximal to the aneurysm will reduce the intralu-
minal pressure and induce thrombosis of the aneurysm.
Occlusion of the parent vessel(s) distal to the aneurysm
creates high resistance in the aneurysm, leading to stagna-
tion of flow and intraluminal thrombosis.
Excision or resection of the aneurysm itself is rarely
needed. Even the “super giant” MCA aneurysms (diam-
eter ≥ 4 cm) can usually be left in place because once the
turbulent flow in the aneurysm ceases, the aneurysm stops
expanding, and the thrombosed mass may even decrease
in size in the long run. However, sometimes the abrupt
thrombosis of a giant aneurysm, together with the increas-
ing edema caused by surgical manipulation of the brain,
may lead to increasing mass effect, necessitating throm-
bectomy and aneurysm resection for decompression.
Traditionally, the ultimate goal of treatment of com-
plex and giant aneurysms has been exclusion of the aneu-
rysm from the circulation. However, a complete occlusion
of the aneurysm by clip closure, trapping, or endovascu-
lar coiling should not always be an aim if perforating or
distal branch arteries arise from the aneurysmal segment.
Partial trapping and flow alteration to reduce flow or in-
duce thrombosis may be adequate to improve the natural
history of the aneurysm.19
Fair results have been reported
for stent-assisted coiling of wide-necked aneurysms and
partial coil-embolization of aneurysms with incorporat-
ed branch origins.16,47
A case of a fusiform M1 aneurysm
treated successfully with a flow-diverting stent without
coiling was described by Pumar et al.30
Flow Requirements
The full flow replacement required for the entire
MCA territory is 50 ± 25 ml/min.1
A robust STA or OA
may have a flow capacity of up to 100 ml/min and can
supply the whole MCA region. This kind of replacement
flow is needed for treatment of an M1 aneurysm. When
necessary, both STA branches may be anastomosed to
two different M2 trunks (one to each) to treat an M1 or a
bifurcation aneurysm. If only one M2 territory or a more
distal branch territory is to be replaced, the flow demand
Fig. 2. Case 13. Preoperative (left) and postoperative (right) antero-
posterior DS angiograms. Digital subtraction angiography performed in
this 22-year-old man revealed a partially thrombosed giant MCA bifur-
cation aneurysm on the right side (left panel). Both STA branches were
used to make 2 bypasses, one to each M2 main trunk distal branch, and
the aneurysm was then trapped with clips. Postoperative angiography
(right) demonstrated the bypass supplying the distal MCA branches but
no contrast filling of the aneurysm.
Fig. 3. Case 20. Preoperative anteroposterior (A) and lateral (B) DS angiograms and postoperative CT angiogram (C). A giant
fusiform aneurysm in the distal branch of the left MCA was seen in the anteroposterior (A) and lateral (B) DS angiograms obtained
in a 12-year-old girl examined for severe headaches. An STA-MCA bypass was performed, followed by proximal clip occlusion of
the parent artery. Postoperative CTA (C) demonstrated a patent bypass and no filling of the aneurysm.

9. L. Kivipelto et al.
406 J Neurosurg / Volume 120 / February 2014
is relatively low, and an ordinary STA flow will be suf-
ficient. However, if the STA is not available or appears
inadequate, an EC-IC or IC-IC bypass with a venous or
arterial interpositioned graft, side-to-side in situ anasto-
mosis, branch reimplantation, or aneurysm excision with
interpositioned grafting may be performed to achieve the
desired revascularization.31,36
We applied the vein graft/ELANA method quite
liberally during the years 2003–2004 after adopting the
technique in Helsinki. However, we gradually withdrew
from using the ELANA method for MCA aneurysms, as
we found the technique quite complicated and usually not
absolutely necessary because “high flow” bypass is rarely
required in the MCA region in terms of flow demand. As
the bypass flow is often less than 50 ml/min, a saphenous
vein graft used in the ELANA technique may be prone
to early occlusion due to relatively low, turbulent flow
in a disproportionately large venous conduit.41
This may
have been one reason for bypass occlusion among our pa-
tients. In our more recent cases, we have no longer used
the ELANA technique in bypasses for MCA aneurysms.
There is great variability in the anatomy and func-
tionality of the leptomeningeal anastomoses of the cere-
bral arterial territories.5,45
Although the MCA is generally
considered an “end artery,” its various natural anastomot-
ic connections may explain the interindividual variability
of tolerance to MCA branch occlusions. Moreover, in-
creasing flow in leptomeningeal collaterals can lead to de-
creasing flow in the bypass, resulting in a delayed bypass
occlusion with no or only mild neurological symptoms.46
This was also observed among our patients: the natural
collaterals “take over” and eventually make the bypass
unnecessary. Similar collateral variability exists also in
the internal capsule and basal ganglion area and probably
explains why certain patients suffered permanent deficits
after M1 aneurysm treatment (in this study, unintentional
occlusion of lenticulostriate perforators) while only tran-
sient deficits were seen in some others, even after com-
plete trapping of M1 aneurysms.19,37
Aneurysm Obliteration
Aneurysm obliteration was achieved effectively and
durably among our patients: no recanalization of aneu-
rysms was detected during a mean follow-up of 27 months.
Early retreatment to occlude the aneurysm was needed
in only 1 case, in which the aneurysm continued filling
briskly despite the distal clip occlusion, and we ended up
partially resecting and clipping the aneurysm 3 days after
the first surgery.
High recanalization rates (35%–87%) are encoun-
tered after endovascular Guglielmi detachable coil em-
bolization of large and giant aneurysms.18,27
Although
uncommon, aneurysm regrowth and rupture have been
reported after bypass and parent vessel occlusion,20,35
and
we conclude that in cases in which complete trapping of
the aneurysm has not been performed, lifelong follow-up
of patients is indicated.
Clinical Outcome
Although the number of cases is low to make statis-
tical conclusions with respect to the different subgroups,
we did observe that most of the significant clinical com-
plications were associated with M1 segment aneurysms:
1 patient died and 4 (57%) of 7 patients had symptomatic
brain infarctions with an increase in mRS score. Fortu-
nately, 3 of these patients recovered to independent life
despite their morbidity. Nevertheless, the median mRS
score among the patients with M1 aneurysms increased
from 0 preoperatively to 2 at the latest follow-up. In con-
trast, there was no significant postoperative morbidity in
the group of patients with bifurcation aneurysms. The 9
patients with a distal MCA aneurysm had a median mRS
score of 0 both preoperatively and at follow-up. The pre-
vious studies have not addressed the different subgroups
of MCA aneurysms stratified by anatomical location, and
therefore our observations cannot be compared with ear-
lier published experience.
Three of the 4 patients who had a “super giant” aneu-
TABLE 6: Summary of publications on MCA aneurysms treated with bypass–vessel occlusion method*
Authors & Year
No. of
Cases
EC-IC
Bypass
IC-IC
Bypass
or
Reconstr
Aneurysm
Excision/
Resection Clipping
Total
Trapping
Partial
Trapping
Aneur
Oblit
(%)
Bypass
Patency
(%)
Mortality
(%)
Morbidity
(%)
Exc/
Good
Recov
(%)
FU
(yrs)
Anson et al., 1996 9 5 4 4 3 2 10 90 2.8
Hoh et al., 2001 7 6 1 1 5 1 69 10 6 86
Quiñones-Hinojosa
& Lawton, 2005
5 5 3 100 80 0 0 100
Sekhar et al., 2005 7 7 5 2 100 100 0 14 100 5.5
Van Doormaal et al.,
2008
22 2 20 8 11 86 5 36 77 3.6
Sanai et al., 2009 16 7 9 98 91 0 5 90 3.4
Shi et al., 2009 6 6 6 (endo-
vasc)
67 NA 0 50 83 2.6
Seo et al., 2009 9 7 2 4 3 2 100 NA 11 22 67 2.1
Kalani et al., 2013 16 16 1 13 75 94 0 31 94 4.9
* Exc = excellent; reconstr = reconstruction; recov = recovery.

10. J Neurosurg / Volume 120 / February 2014
Bypass and vessel occlusion for complex MCA aneurysms
407
rysm (diameter ≥ 4 cm) and underwent resection of the an-
eurysm had an unfavorable outcome. Whether this was a
consequence of manipulation of the already compromised
brain or related to the nature of the pathology treated is
not clear.
Three patients with M1 aneurysms suffered a periop-
erative stroke due to perforating artery thrombosis despite
a partial trapping. This complication could probably not
have been prevented by choosing any other surgical meth-
od. Whether a flow-diverting stent would have resulted in
a better outcome by saving the perforators remains uncer-
tain. In this study the fusiform M1 aneurysm (Case 6) in
which a flow diverter had been deployed 5 months earlier
continued growing, necessitating surgical treatment.
Suggestions for Treatment Strategies
We propose slightly different treatment strategies and
principles for consideration, depending on the aneurysm’s
location in the MCA vascular tree.
M1 Aneurysms. Complex M1 aneurysms are typically
fusiform, and direct clipping or coil embolization is usu-
ally not feasible. The aneurysmal segment often involves
origins of vital lenticulostriate perforating arteries, further
restricting the options for treating the aneurysm. Proximal
or distal occlusion should be preferred to trapping. After
performing the bypass, a flow alteration is induced by
proximal or distal occlusion of the parent artery, aiming
at aneurysm obliteration with preservation of flow in the
perforating branches. It must be understood, however, that
this kind of deliberate hemodynamic modification and
thrombotic process may be unpredictable and still carries
the risk of perforator occlusion.
Future development of flow diverters may provide
useful treatment alternatives for M1 aneurysms, in par-
ticular, with the objective of saving the perforators and
reducing the shear stress on the aneurysm walls.
MCA Bifurcation Aneurysms. Complex MCA bifurca-
tion aneurysms may be treated by clipping the neck to-
gether with one of the incorporated M2 branches protected
with a bypass, assuming that the inflow to the other M2
can be preserved. If this is not feasible, both M2 branches
must be revascularized followed by proximal parent ar-
tery occlusion (distal M1 occlusion) or distal occlusion
(both M2 segments distal to the aneurysm). Trapping is
also an option if no significant perforators arise from the
base of the aneurysm.
Distal MCA Aneurysms. Complex aneurysms of M2
or more distal segments, when fusiform and large, can be
treated by distal revascularization followed by occlusion
of either the afferent or efferent parent vessel, resulting
in aneurysm thrombosis. Trapping will give a definitive
result immediately and is often feasible as perforating
branches are rarely a problem.
Conclusions
Surgical treatment with bypass and occlusion method
of treating complex MCA aneurysms appears to result
in durable, often definitive protection from hemorrhage
and further aneurysm growth, with a mortality rate and
clinical outcome that are clearly superior to those associ-
ated with the natural history of these difficult aneurysms.
Partial trapping should be favored for M1 fusiform aneu-
rysms, as vital perforating branches often originate in the
aneurysmal segment wall.
Disclosure
The authors report no conflict of interest concerning the mate-
rials or methods used in this study or the findings specified in this
paper.
Author contributions to the study and manuscript preparation
include the following. Conception and design: Kivipelto. Acquisition
of data: Kivipelto, Meling. Analysis and interpretation of data: Kivi-
pelto. Drafting the article: Kivipelto. Critically revising the article:
all authors. Reviewed submitted version of manuscript: all authors.
Approved the final version of the manuscript on behalf of all authors:
Kivipelto. Administrative/technical/material support: Hernesniemi.
Study supervision: Kivipelto.
References
1. Amin-Hanjani S, Alaraj A, Charbel FT: Flow replacement
bypass for aneurysms: decision-making using intraoperative
blood flow measurements. Acta Neurochir (Wien) 152:1021–
1032, 2010
2. Anson JA, Lawton MT, Spetzler RF: Characteristics and sur-
gical treatment of dolichoectatic and fusiform aneurysms. J
Neu­rosurg 84:185–193, 1996
3. Ausman JI, Diaz FG, Sadasivan B, Gonzeles-Portillo M Jr,
Malik GM, Deopujari CE: Giant intracranial aneurysm sur-
gery: the role of microvascular reconstruction. Surg Neurol
34:8–15, 1990
4. Barrow DL, Alleyne C: Natural history of giant intracranial
aneurysms and indications for intervention. Clin Neurosurg
42:214–244, 1995
5. Brozici M, van der Zwan A, Hillen B: Anatomy and functional-
ity of leptomeningeal anastomoses: a review. Stroke 34:2750–
2762, 2003
6. Charbel FT, Meglio G, Amin-Hanjani S: Superficial temporal
artery-to-middle cerebral artery bypass. Neurosurgery 56 (1
Suppl):186–190, 2005
7. Choudhari KA: Wrapping and coating of cerebral aneurysms:
history, evolution and surgical management after a re-bleed.
Br J Neurosurg 18:259–267, 2004
8. Cognard C, Weill A, Spelle L, Piotin M, Castaings L, Rey A,
et al: Long-term angiographic follow-up of 169 intracranial
berry aneurysms occluded with detachable coils. Radiology
212:348–356, 1999
9. Dashti R, Hernesniemi J, Niemelä M, Rinne J, Lehecka M,
Shen H, et al: Microneurosurgical management of distal mid-
dle cerebral artery aneurysms. Surg Neurol 67:553–563, 2007
10. Dashti R, Hernesniemi J, Niemelä M, Rinne J, Porras M,
Lehecka M, et al: Microneurosurgical management of middle
cerebral artery bifurcation aneurysms. Surg Neurol 67:441–
456, 2007
11. Dashti R, Rinne J, Hernesniemi J, Niemelä M, Kivipelto L,
Lehecka M, et al: Microneurosurgical management of proxi-
mal middle cerebral artery aneurysms. Surg Neurol 67:6–14,
2007
12. Day AL, Gaposchkin CG, Yu CJ, Rivet DJ, Dacey RG Jr: Spon-
taneous fusiform middle cerebral artery aneurysms: character-
istics and a proposed mechanism of formation. J Neurosurg
99:228–240, 2003
13. Deshmukh VR, Kakarla UK, Figueiredo EG, Zabramski JM,
Spetzler RF: Long-term clinical and angiographic follow-up of
un­clippable wrapped intracranial aneurysms. Neurosurgery
58:434–442, 2006
14. Drake CG, Peerless SJ: Giant fusiform intracranial aneurysms:

11. L. Kivipelto et al.
408 J Neurosurg / Volume 120 / February 2014
review of 120 patients treated surgically from 1965 to 1992. J
Neurosurg 87:141–162, 1997
15. Drake CG, Peerless SJ, Hernesniemi JA: Surgery of Vertebro­
basilar Aneurysms: London, Ontario Experience on 1767
Patients. Vienna: Springer-Verlag, 1996
16. Fields JD, Brambrink L, Dogan A, Helseth EK, Liu KC, Lee
DS, et al: Stent assisted coil embolization of unruptured mid-
dle cerebral artery aneurysms. J Neurointerv Surg 5:15–19,
2013
17. Gonzalez NR, Duckwiler G, Jahan R, Murayama Y, Viñuela F:
Challenges in the endovascular treatment of giant intracranial
aneurysms. Neurosurgery 62 (6 Suppl 3):1324–1335, 2008
18. Gruber A, Killer M, Bavinzski G, Richling B: Clinical and an-
giographic results of endosaccular coiling treatment of giant
and very large intracranial aneurysms: a 7-year, single-center
experience. Neurosurgery 45:793–804, 1999
19. Hoh BL, Putman CM, Budzik RF, Carter BS, Ogilvy CS: Com-
bined surgical and endovascular techniques of flow alteration
to treat fusiform and complex wide-necked intracranial aneu-
rysms that are unsuitable for clipping or coil embolization. J
Neu­rosurg 95:24–35, 2001
20. Isla A, Alvarez F, Roda JM, Muñoz J, Morales C, Garcia Blaz­
quez M: Serpentine aneurysm: regrowth after a superficial
tem­poral artery-middle cerebral artery bypass and internal
ca­rotid artery ligation: case report. Neurosurgery 34:1072–
1074, 1994
21. Jafar JJ, Russell SM, Woo HH: Treatment of giant intracranial
aneurysms with saphenous vein extracranial-to-intracranial
bypass grafting: indications, operative technique, and results
in 29 patients. Neurosurgery 51:138–146, 2002
22. Jahromi BS, Mocco J, Bang JA, Gologorsky Y, Siddiqui AH,
Horowitz MB, et al: Clinical and angiographic outcome after
endovascular management of giant intracranial aneurysms.
Neurosurgery 63:662–675, 2008
23. Kalani MY, Zabramski JM, Hu YC, Spetzler RF: Extracranial-
intracranial bypass and vessel occlusion for the treatment of
unclippable giant middle cerebral artery aneurysms. Neuro­
surgery 72:428–436, 2013
24. Lawton MT, Hamilton MG, Morcos JJ, Spetzler RF: Revascu-
larization and aneurysm surgery: current techniques, indica-
tions, and outcome. Neurosurgery 38:83–94, 1996
25. Lawton MT, Quiñones-Hinojosa A, Chang EF, Yu T: Throm-
botic intracranial aneurysms: classification scheme and man-
agement strategies in 68 patients. Neurosurgery 56:441–454,
2005
26. Lawton MT, Spetzler RF: Surgical management of giant intra-
cranial aneurysms: experience with 171 patients. Clin Neuro­
surg 42:245–266, 1995
27. Murayama Y, Nien YL, Duckwiler G, Gobin YP, Jahan R,
Frazee J, et al: Guglielmi detachable coil embolization of ce-
rebral aneurysms: 11 years’ experience. J Neurosurg 98:959–
966, 2003
28. Navratil O, Lehecka M, Lehto H, Dashti R, Kivisaari R,
Niemelä M, et al: Vascular clamp-assisted clipping of thick-
walled giant aneurysms. Neurosurgery 64 (3 Suppl):ons113–
ons121, 2009
29. Newell DW, Vilela MD: Superficial temporal artery to middle
cerebral artery bypass. Neurosurgery 54:1441–1449, 2004
30. Pumar JM, Lete I, Pardo MI, Vázquez-Herrero F, Blanco M:
LEO stent monotherapy for the endovascular reconstruction of
fusiform aneurysms of the middle cerebral artery. AJNR Am
J Neuroradiol 29:1775–1776, 2008
31. Quiñones-Hinojosa A, Lawton MT: In situ bypass in the man-
agement of complex intracranial aneurysms: technique appli-
cation in 13 patients. Neurosurgery 57 (1 Suppl):140–145,
2005
32. Randell T, Niemelä M, Kyttä J, Tanskanen P, Määttänen M,
Karatas A, et al: Principles of neuroanesthesia in aneurysmal
subarachnoid hemorrhage: the Helsinki experience. Surg Neu­
rol 66:382–388, 2006
33. Rodríguez-Hernández A, Sughrue ME, Akhavan S, Habdank-
Kolaczkowski J, Lawton MT: Current management of middle
cerebral artery aneurysms: surgical results with a “clip first”
policy. Neurosurgery 72:415–427, 2013
34. Sanai N, Zador Z, Lawton MT: Bypass surgery for complex
brain aneurysms: an assessment of intracranial-intracranial
bypass. Neurosurgery 65:670–683, 2009
35. Scott RM, Liu HC, Yuan R, Adelman L: Rupture of a previ-
ously unruptured giant middle cerebral artery aneurysm after
extracranial-intracranial bypass surgery. Neurosurgery 10:
600–603, 1982
36. Sekhar LN, Stimac D, Bakir A, Rak R: Reconstruction options
for complex middle cerebral artery aneurysms. Neurosurgery
56 (1 Suppl):66–74, 2005
37. Seo BR, Kim TS, Joo SP, Lee JM, Jang JW, Lee JK, et al: Sur-
gical strategies using cerebral revascularization in complex
middle cerebral artery aneurysms. Clin Neurol Neurosurg
111:670–675, 2009
38. Shi ZS, Ziegler J, Duckwiler GR, Jahan R, Frazee J, Ausman
JI, et al: Management of giant middle cerebral artery aneu-
rysms with incorporated branches: partial endovascular coil-
ing or combined extracranial-intracranial bypass—a team ap-
proach. Neurosurgery 65 (6 Suppl):121–131, 2009
39. Steinberg GK, Drake CG, Peerless SJ: Deliberate basilar or
vertebral artery occlusion in the treatment of intracranial an-
eurysms. Immediate results and long-term outcome in 201 pa-
tients. J Neurosurg 79:161–173, 1993
40. Sughrue ME, Saloner D, Rayz VL, Lawton MT: Giant intra-
cranial aneurysms: evolution of management in a contempo-
rary surgical series. Neurosurgery 69:1261–1271, 2011
41. Sundt TM III, Sundt TM Jr: Principles of preparation of vein
bypass grafts to maximize patency. J Neurosurg 66:172–180,
1987
42. Tulleken CA, Verdaasdonk RM: First clinical experience with
Excimer assisted high flow bypass surgery of the brain. Acta
Neurochir (Wien) 134:66–70, 1995
43. Tulleken CA, Verdaasdonk RM, Beck RJ, Mali WP: The modi-
fied excimer laser-assisted high-flow bypass operation. Surg
Neurol 46:424–429, 1996
44. Tulleken CA, Verdaasdonk RM, Mansvelt Beck HJ: Nonoc-
clusive excimer laser-assisted end-to-side anastomosis. Ann
Thorac Surg 63 (6 Suppl):S138–S142, 1997
45. van der Zwan A, Hillen B, Tulleken CA, Dujovny M, Dragovic
L: Variability of the territories of the major cerebral arteries. J
Neurosurg 77:927–940, 1992
46. van Doormaal TP, van der Zwan A, Verweij BH, Han KS,
Langer DJ, Tulleken CA: Treatment of giant middle cerebral
artery aneurysms with a flow replacement bypass using the ex-
cimer laser-assisted nonocclusive anastomosis technique. Neu­
rosurgery 63:12–22, 2008
47. Vendrell JF, Costalat V, Brunel H, Riquelme C, Bonafe A:
Stent-assisted coiling of complex middle cerebral artery aneu-
rysms: initial and midterm results. AJNR Am J Neuroradiol
32:259–263, 2011
48. Wiebers DO, Whisnant JP, Huston J III, Meissner I, Brown
RD Jr, Piepgras DG, et al: Unruptured intracranial aneurysms:
natural history, clinical outcome, and risks of surgical and en-
dovascular treatment. Lancet 362:103–110, 2003
49. Yaşargil MG (ed): Microsurgery Applied to Neurosurgery.
Stuttgart: Georg Thieme, 1969
Manuscript submitted April 12, 2013.
Accepted August 10, 2013.
Please include this information when citing this paper: published
online November 29, 2013; DOI: 10.3171/2013.10.JNS13738.
Address correspondence to: Leena Kivipelto, M.D., Ph.D.,
De­part­ment of Neurosurgery, Helsinki University Hospital, Topeli-
uksenkatu 5, 00260 Helsinki, Finland. email: leena.kivipelto@hus.fi.