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CASE SERIES
Contralateral Anterior Interhemispheric Approach
to Medial Frontal Arteriovenous Malformations:
Surgical Technique and Results
Ahmad Hafez, MD∗ ‡§
BACKGROUND: Medial frontal arteriovenous malformations (AVMs) require opening the
interhemispheric fissure and are traditionally accessed through an ipsilateral anterior interhemispheric approach (IAIA). The contralateral anterior interhemispheric approach (CAIA)
flips the positioning with the midline still positioned horizontally for gravity retraction, but
with the AVM on the upside and the approach from the contralateral, dependent side.
OBJECTIVE: To determine whether the perpendicular angle of attack associated with the
IAIA converts to a more favorable parallel angle of attack with the CAIA.
METHODS: The CAIA was used in 6 patients with medial frontal AVMs. Patients and AVM
characteristics, as well as pre- and postoperative clinical and radiographic data, were
reviewed retrospectively.
RESULTS: Four patients presented with unruptured AVMs, with 5 AVMs in the dominant,
left hemisphere. The lateral margin was off-midline in all cases, and average nidus size
was 2.3 cm. All AVMs were resected completely, as confirmed by postoperative catheter
angiography. All patients had good neurological outcomes, with either stable or improved
modified Rankin Scores at last follow-up.
CONCLUSIONS: This study demonstrates that the CAIA is a safe alternative to the IAIA
for medial frontal AVMs that extend 2 cm or more off-midline into the deep frontal white
matter. The CAIA aligns the axis of the AVM nidus parallel to the exposure trajectory, brings
its margins in view for circumferential dissection, allows gravity to deliver the nidus into
the interhemispheric fissure, and facilitates exposure of the lateral margin for the final
dissection, all without resecting or retracting adjacent normal cortex.
Kunal P. Raygor, MD∗§
Michael T. Lawton, MD∗
∗
Department of Neurological Surgery,
University of California, San Francisco,
San Francisco, California; ‡ Department of
Neurosurgery, Helsinki University Central
Hospital, Helsinki, Finland
§
These authors contributed equally to
this work.
Correspondence:
Michael T. Lawton, MD,
University of California San Francisco,
Department of Neurosurgery,
505 Parnassus Avenue, M780,
San Francisco, CA 94143.
E-mail: [email protected]
Received, July 17, 2016.
Accepted, January 10, 2017.
C 2017 by the Congress of
Copyright Neurological Surgeons
KEY WORDS: Arteriovenous malformation, Medial frontal lobe, Contralateral anterior interhemispheric
approach, Ipsilateral anterior interhemispheric approach, AVM resection
Operative Neurosurgery 00:1–9, 2017
I
n a previous review of 132 patients with
parafalcine and midline arteriovenous
malformations (AVMs), we exposed all
AVMs with a bilateral craniotomy across the
superior sagittal sinus (SSS) and a wide opening
of the interhemispheric fissure to access deep
feeders from the anterior and posterior cerebral
arteries, as well as important draining veins
on the medial hemisphere.1 The bilateral
ABBREVIATIONS: AVM, arteriovenous malformations; IAIA, ipsilateral anterior interhemispheric
approach; CAIA, contralateral anterior interhemispheric approach; SSS, superior sagittal sinus; mRS,
modified Rankin Score; MRI, magnetic resonance
imaging; AIFA, anterior inferior frontal artery
OPERATIVE NEUROSURGERY
DOI: 10.1093/ons/opx004
craniotomy completely exposed the midline
to optimize access and visualization. In all of
these operations, the AVM was approached
ipsilaterally in order to keep the anatomy
completely in view and have full access to the
nidus. With many medial frontal AVMs, an
ipsilateral anterior interhemispheric approach
(IAIA) was used with the midline positioned
horizontally to allow gravity to retract the frontal
lobe ipsilateral to the AVM, creating a deep and
perpendicular perspective with limited access
to the margins of the AVM other than that on
the medial surface. The AVM was dissected
up from the sagging frontal lobe, drawing
the AVM medially into the interhemispheric
fissure with restricted access to the lateral and
deep margins that often receive supply from
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HAFEZ ET AL
challenging lenticulostriate or insular perforating arteries
travelling through deep frontal white matter.
In contrast to the IAIA, the contralateral anterior interhemispheric approach (CAIA) flips the positioning, still with the
midline positioned horizontally for gravity retraction, but with
the AVM on the upside and the approach from the contralateral,
dependent side. This geometry provides the same exposure of
the medial hemisphere and the AVM’s midline anatomy, but
with circumferential dissection around the nidus, gravity delivers
the nidus into the interhemispheric fissure and improves access
to those treacherous lateral and deep margins. In addition,
the crossing midline trajectory requires less retraction and/or
resection of adjacent cortex than the IAIA. Disadvantages of
this CAIA include involvement of the unaffected contralateral
hemisphere, the falx as a barrier to access, a deeper reach to the
lateral border, and a general concern that intraoperative bleeding
would be more difficult to manage from the contralateral side.
With increasing AVM experience, the disadvantages and concerns
associated with the CAIA seemed manageable and offset by
advantages with larger medial frontal AVMs. Therefore, the CAIA
was performed in 6 AVM patients with the hypothesis that the
perpendicular angle of attack associated with the IAIA would
convert to a more favorable parallel angle of attack with the CAIA,
with less retraction, improved working angles, and no measurable
increase in risk.
METHODS
Patients
After obtaining Institutional Review Board approval, we performed
a retrospective review of relevant electronic health records for surgeries
performed by the senior author between January 1998 and March
2016. Six patients underwent resection of their medial frontal AVMs
via the CAIA. The decision to use this technique was made after
reviewing preoperative imaging. Pre- and postoperative clinical and
radiographic data including age, gender, presenting symptoms, AVM
laterality, maximum nidus size, Spetzler-Martin grade,2 Supplementary
grade,3 feeding arteries, draining veins, involved cortical structures,
presence or absence of preoperative embolization, and functional status
as measured by modified Rankin Score (mRS) were obtained and
reviewed.
Surgical Technique for the CAIA
The patient is positioned supine with the ipsilateral shoulder
bolstered. The head is turned 90 degrees to orient the midline horizontally (parallel to the floor), and the head is angled upward 60 degrees.
The ipsilateral hemisphere containing the AVM faces the ceiling (upside)
and gravity retracts the contralateral hemisphere. The head is fixed in
the Mayfield head holder, and surgical neuronavigation is registered to
precisely locate the AVM and plan the craniotomy to avoid bridging
veins. No lumbar drain is used. After making a semicircular scalp
incision, the scalp flap is reflected anteriorly. A single burr hole is drilled
approximately 2 cm lateral to the midline along the posterior aspect of
the craniotomy, after which a bifrontal craniotomy flap is elevated that
2 | VOLUME 00 | NUMBER 0 | 2017
crosses the midline and expose the SSS (Figure 1). More than two-thirds
of the craniotomy flap is on the side contralateral to the AVM. The
dura is opened in a curvilinear flap based along the SSS and tacked up
medially (Figure 1).
Using microsurgical technique, the interhemispheric fissure is opened
widely and the hemisphere contralateral to the AVM is covered with
protective patties. Unlike the IAIA (Figures 1A-1E), no mechanical
brain retraction is needed in the contralateral approach (Figures 1F1J). Anteriorly located AVMs may lie beneath the free edge of the falx
where it is thin, whereas posteriorly located AVMs may lie behind the
falx and require the opening of a falcine window. The trajectory of
the subarachnoid dissection begins in the contralateral interhemispheric
fissure and ends ipsilateral to the AVM after crossing the falx. Feeding
arteries and draining veins may adhere to the falx on the ipsilateral
side, requiring falcine incisions made layer by layer with countertraction
away from the nidus, as well as neuronavigation. Major arterial feeders
are identified, occluding terminal feeders and skeletonizing en passage
arteries. After dearterializing the medial face, the nidus is dissected
circumferentially, exposing the lateral margin of the nidus and mobilizing
it into the interhemispheric fissure to gain clear visualization of the plane
where deep perforating arteries supply the AVM. The draining veins
are cauterized and divided after they darken, allowing the nidus to be
removed en bloc.
RESULTS
Between January 1, 1998 and March 31, 2016, the senior
author (MTL) microsurgically treated a total of 725 AVMs,
of which 26 (3.6%) were located in the medial frontal lobe.
Six recent patients underwent AVM resection using the CAIA
(Table). The median age was 40 (range, 12-55), and patients were
evenly divided by sex. Two patients presented with intracranial
hemorrhage, 2 with headache alone, 1 with seizures, and 1 with
blurry vision and papilledema. All patients were right-handed,
and 5 had AVMs in the left hemisphere. The average AVM
diameter was 2.3 cm, and 2 patients had a nidus greater than
3 cm in diameter. One AVM involved eloquent motor cortex
within the paracentral lobule. Interestingly, deep venous drainage
via anterior or posterior caudate veins to the thalamostriate and
internal cerebral veins was found in 3 patients. Five patients had
Spetzler-Martin grade II AVMs, whereas Supplementary grades
were more variable.
No surgical complications were observed. All AVMs were
resected completely, as confirmed by postoperative catheter
angiography. All patients had good neurological outcomes (mRS
scores 0 or 1), with either stable or improved mRS at last followup. The median duration of follow-up was 73 days (range 39-190
days).
Illustrative Cases
Case 3
A 49-year-old female was diagnosed with a left medial frontal
AVM on magnetic resonance imaging (MRI; Figure 2A) after
papilledema was found during a routine exam for eye-glasses. She
had noted a few years of worsening blurry vision at that time.
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CONTRALATERAL ANTERIOR INTERHEMISPHERIC APPROACH FOR MEDIAL FRONTAL AVMS
OPERATIVE NEUROSURGERY
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HAFEZ ET AL
FIGURE 1. Overview of surgical technique with the IAIA and CAIA. A, For the IAIA, the head is positioned with midline horizontal (scalp incision (dashed line),
burr hole (white circle), and bifrontal craniotomy (solid line)), the right AVM on the down side, and B the neck angled 45 degrees upwards. C, In the coronal
cross-sectional view, the neurosurgeon’s point of view is almost vertically downward towards the dependent medial hemisphere, which makes the lateral margin (green
star) inaccessible without additional retraction or tissue resection along the dashed arrow. D, Surgeon’s view demonstrates excellent access to the medial AVM margin
and feeders from the right pericallosal artery (PcaA), but E the nidus must be mobilized into the interhemispheric fissure against gravity and the frontal lobe must
be retracted or some tissue resected to circumdissect the lateral margin (dashed arrow, coronal cross-sectional view). F, For the CAIA, the head is positioned with
midline horizontal (scalp incision (dashed line), burr hole (white circle), and bifrontal craniotomy (solid line)), the left AVM on the up side, and G the neck angled
60 degrees upwards. H, In the coronal cross-sectional view, the neurosurgeon’s point of view is almost horizontal over the dependent medial hemisphere and across the
interhemispheric fissure, which makes the lateral margin (green star) accessible without additional retraction or tissue resection. I, Surgeon’s view demonstrates excellent
access to the medial AVM margin and feeders from the left pericallosal artery after incising and resecting a piece of the falx (see inset). J, The nidus falls into the
interhemispheric fissure with gravity, providing a direct view of the lateral margin, thereby facilitating circumdissection of the AVM’s most difficult margin (dashed
arrow, coronal cross-sectional view). Abbreviations: SSS = superior sagittal sinus; ISS = inferior sagittal sinus; CC = corpus callosum.
TABLE. Patient and AVM Characteristics for Patients Undergoing the CAIA to AVM Resection
Case
Age
(yrs),
sex
1
15, M
2
3
48, F
49, F
4
12, M
5
6
55, M
32, F
Presenting
symptoms
Side of
AVM
Nidus
size
(cm)
SM
grade
Supp
grade
Feeding
arteries
Draining
vein(s)
Structures
involved
Preop
Embo
Preop
mRS
Postop EBL
mRS
(mL)
HA, seizure,
ICH
HA
Blurry vision
and
papilledema
Prior ICH,
recovered
Left
1.7
2
1
CmaA
AntCaudV
Cing Crtx
0
1
1
400
Left
Left
1
2.5
2
2
4
4
PcaA, CmaA
AIFA, FrPolA,
CmaA, PcaA
AntCaudV
MedFrontV,
PcaV
Cing Crtx
Cing Crtx
0
1
1
1
0
0
300
500
Left
1.7
3
2
PcaA,
ParaCenA
PostCaudV
0
0
0
200
Seizure
HA
Right
Left
3.1
3.5
2
2
4
3
FrPolA, CmaA MedFrontV
AIFA, PcaA
MedFrontV
Cing Crtx,
Paracentral
lobule
Cing Crtx
Cing Crtx
0
1
1
1
1
0
500
300
ABBREVIATIONS: AIFA, anterior internal frontal artery; AntCaudV, anterior caudate vein; Cing Crtx, cingulate cortex; CmaA, callosomarginal artery; EBL, estimated blood loss;
Embo, embolization; FrPolA, frontopolar artery; HA, headache; ICH, intracranial hemorrhage; MedFrontV, medial frontal vein; mL, milliliter; mRS, modified Rankin Score; ParaCenA,
paracentral artery; PcaA, pericallosal artery; PcaV, pericallosal vein; PostCaudV, posterior caudate vein; SM, Spetzler-Martin; SSS, superior sagittal sinus; Supp, Supplementary.
Preoperative angiogram demonstrated feeders from the anterior
inferior frontal artery (AIFA), frontopolar, callosomarginal, and
pericallosal arteries, and venous drainage through medial frontal
and pericallosal veins (Figures 2B and 2C). The largest feeding
artery from AIFA was embolized preoperatively, as was an
intranidal aneurysm. The AVM was resected through the CAIA.
After opening the interhemispheric fissure widely, subarachnoid
dissection was carried down to the corpus callosum and the falx
was divided (Figure 2D) to provide view of the 4 trunks feeding
the AVM. The trunk that had been completely embolized was
clip-occluded, cauterized, and divided; the others were skeletonized to preserve en passage arteries (Figure 2E). A plane
of dissection was developed anteriorly, posteriorly, and laterally
around the nidus, allowing the nidus to be pulled into the
interhemispheric fissure. The draining veins were divided and
the nidus was removed (Figure 2F). Postoperatively, the patient
did well, with slight improvement in her vision and no new
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neurological deficits. Postoperative angiogram showed no residual
AVM nidus (Figures 2G and 2H).
Case 6
A 32-year-old female was seen in clinic after an MRI performed
for persistent headaches revealed a left medial frontal AVM
(Figure 3A). Initial angiogram demonstrated AIFA and pericallosal feeding arteries and superficial venous drainage from anterior
medial frontal veins (Figures 3B and 3C). She underwent preoperative embolization of the 2 major feeding arteries. Intraoperatively, the anterior cerebral artery was followed along its course
to get around the dilated draining veins (Figure 3D). The AVM
was dissected circumferentially to occlude all feeders, and the
draining vein was divided to remove the nidus (Figures 3E3G). Postoperatively, the patient did well, with resolution of her
frontal headaches and no new neurological deficits. Postoperative
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CONTRALATERAL ANTERIOR INTERHEMISPHERIC APPROACH FOR MEDIAL FRONTAL AVMS
A
B
C
D
E
G
H
F
FIGURE 2. Pre-, intra-, and postoperative images from Case 3. A, Preoperative axial MRI demonstrating a left medial
frontal AVM with multiple dilated veins anterior and posterior to the nidus making an ipsilateral approach treacherous. B,
C Preoperative anteroposterior (AP) and lateral digital subtraction angiography (DSA) demonstrating the left medial frontal
AVM with its associated arterial feeders and draining veins. D, Intraoperative photo demonstrating division of the falx cerebri.
E, Intraoperative photo demonstrating skeletonized feeding arteries. F, Intraoperative photo of the AVM nidus after it is pulled
into the contralateral interhemispheric fissure. G, H Postoperative AP and lateral DSA showing no residual arteriovenous (AV)
shunting.
angiogram showed no residual AVM nidus and preservation of en
passage arteries (Figures 3H and 3I).
DISCUSSION
Contralateral approaches through the interhemispheric fissure
are designed for accessing lesions located laterally in or adjacent
to the lateral ventricle.4-6 With the contralateral transcallosal
approach, the head is positioned with the midline oriented
horizontally and the lesion on the upside to allow gravity
OPERATIVE NEUROSURGERY
to retract the dependent hemisphere and open the interhemispheric fissure without retractor blades.7 A crossing trajectory
begins in the anterior interhemispheric fissure contralateral to
the lesion but ends in the ventricle ipsilateral to the lesion,
thereby maximizing the lateral exposure in the ventricle to
comfortably access small AVMs in the ventricular wall, caudate
head, and thalamus. Similar advantages in exposure and access
result from gravity retraction and a crossing trajectory with
the CAIA to lesions in the medial frontal lobe that are not
strictly intra- or periventricular. However, this approach has
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HAFEZ ET AL
A
B
C
D
E
F
G
H
I
FIGURE 3. Pre-, intra-, and postoperative images from Case 6. A, Preoperative coronal MRI demonstrating a left medial
frontal AVM. B, C, Preoperative AP and lateral DSA demonstrating the left medial frontal AVM with its associated arterial
feeders and draining veins. D, E, Intraoperative photos demonstrating identification and then cauterization of arterial feeders.
F, Intraoperative photo showing removal of the nidus after dividing the draining veins. G, Intraoperative photo showing
preservation of en passage arteries. H, I, Postoperative AP and lateral DSA showing no residual AV shunting.
not been widely used with AVMs for several reasons. First, an
approach from the contralateral side exposes both hemispheres
to surgical manipulation and risk of injury. Second, the falx
is a midline barrier that conceals AVM anatomy and must
be incised or excised to access the lesion. Third, the surgical
corridor is deepened with a crossing trajectory. And finally,
intraoperative AVM hemorrhage at increased depths and in a
hemisphere that is only minimally exposed by the craniotomy
might be more dangerous and difficult to control. Therefore,
the IAIA has been the predominant approach to medial frontal
AVMs.8
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Medial frontal AVMs with a lateral margin that extends 2 cm or
more from the midline are difficult to remove safely through the
IAIA mainly because the exposure of this lateral margin is poor.
When the AVM lies in the dependent hemisphere, the medial
aspect of the superior frontal gyrus conceals the AVM’s lateral
margin and must be retracted or resected to access this margin.
Retraction or brain resection with medial frontal AVMs that
are more posterior can damage motor and supplementary motor
cortex. Furthermore, AVMs that exceed this 2-cm dimension are
more likely to be supplied by lenticulostriate arteries traversing
deep frontal white matter that can be difficult to cauterize and
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CONTRALATERAL ANTERIOR INTERHEMISPHERIC APPROACH FOR MEDIAL FRONTAL AVMS
control. Therefore, the lateral margin is the most dangerous one
to dissect and has the worst exposure with the IAIA. In addition,
medial veins ascending to the SSS typically drain the AVM and
can tether the hemisphere, limiting widening of the interhemisphere fissure by gravity retraction. These veins must be preserved
for AVM outflow throughout the resection, and an ipsilateral
approach places them in the center of the operative field where
they become obstacles at risk with the passages and movements
of surgical instruments.
Therefore, the IAIA is not ideal for these medium-sized, medial
frontal AVMs, and the CAIA has important advantages with
these particular AVMs that offset its risks. This rationale justified
our experience with the CAIA in the 6 patients presented. We
did not observe any injury or neurological morbidity in the
contralateral hemisphere resulting from our surgical manipulations. Bridging veins in the dependent hemisphere and the risk of
venous infarction were our biggest concerns, but these veins were
scarce and easily preserved. Neuronavigation was useful in identifying them preoperatively and relocating the craniotomy flap to
avoid them. The falx was easily transected to expose the AVM
anatomy on the opposite side of the interhemispheric fissure.
Although the surgical corridor was deeper than with an IAIA,
we did not struggle at the depths of the circumdissection. On
the contrary, dissection of the lateral margin was facilitated by a
view directly into this plane, a nidus that mobilized medially to
widen this plane, and direct access to lenticulostriate perforators
as they intersected the lateral and deep margins. Intraoperative
AVM hemorrhage was not encountered in this series, but could
have been managed easily from the contralateral side. Although
this study was a small, highly selected, retrospective surgical series
and reflects the experience of a specialized vascular surgeon with
a large AVM experience and a well-trained team, results confirm
the advantages and safety of the CAIA for medial frontal AVMs.
The angle of attack with medial frontal AVMs changes from
perpendicular with the IAIA to a parallel with the CAIA. With the
IAIA, the axis of the AVM nidus is perpendicular to the trajectory
of the exposure, which means that only one side of the AVM is
accessed directly and other sides are accessed only with retraction
and/or resection of brain and mobilization of the AVM into the
interhemispheric fissure. With the CAIA, the axis of the AVM
nidus is parallel to the trajectory of the exposure, bringing most
of its margins in view and accessing it circumferentially for easy
dissection. As circumdissection frees the margins, gravity delivers
the AVM into the interhemispheric fissure and widens the lateral
margin for the final dissection, which increases the safety of the
most treacherous part of the resection.
The CAIA requires incisions in the falx with arteriovenous
structures hidden on the opposite side. Neuronavigation helps
plan these cuts and avoid these hazards. Complete removal of
the adjacent piece of falx enhances the exposure. The inferior
sagittal sinus can be occluded when it does not drain the AVM,
enabling these cuts to extend through the free edge of the falx.
The limited transfalcine view requires detailed knowledge of
medial frontal lobe surface anatomy.9 The anterior frontal median
OPERATIVE NEUROSURGERY
cortex is defined: inferiorly by pericallosal arteries separating
the cingulate gyrus from the corpus callosum; posteriorly by
the paracentral lobule and eloquent motor cortex; anteriorly
by the medial aspect of superior frontal gyrus and callosomarginal artery’s branches; and superiorly by the SSS and its
associated bridging veins. Orbitofrontal and frontopolar arteries
supply anterior medial frontal AVMs, whereas the internal frontal
and paracentral arteries supply posterior medial frontal AVMs.
Pericallosal and callosomarginal arteries feed cingulate AVMs
directly. Venous drainage usually ascends to the SSS through
medial frontal veins, but cingulate AVMs often have descending
venous drainage to pericallosal veins, inferior sagittal sinus, and
occasionally deep to the internal cerebral veins, as seen in our
cohort.1
The CAIA is not recommended for all medial frontal AVMs.
Small AVMs confined to or just off the midline may not
benefit from a contralateral approach. Ruptured AVMs may have
associated hematomas and presenting neurological deficits that
favor an ipsilateral approach through the hematoma cavity. A
medial frontal AVM with a hematoma extending to a cortical
surface may be managed best with a transcortical approach, which
would require the AVM to be positioned on the upside.
CONCLUSION
This study demonstrates that the CAIA is a safe alternative
to the IAIA for medial frontal AVMs that extend 2 cm or more
off the midline into the deep frontal white matter. The CAIA
aligns the axis of the AVM nidus parallel to the trajectory of the
exposure, bringing most of its margins in view for circumferential
dissection, allowing gravity to deliver the AVM into the interhemispheric fissure, and facilitating exposure of the lateral margin
for the final dissection, all without resecting or retracting adjacent
normal cortex.
Disclosures
Dr Hafez was awarded the C. Ehrnrooth Fellowship (Fondation de Luxembourg) at the Clinic of Neurosurgical Surgical of the Helsinki University Central
Hospital. The authors have no personal, financial, or institutional interest in any
of the drugs, materials, or devices described in this article.
REFERENCES
1. Kim YB, Young WL, Lawton MT, Project UBS. Parafalcine and midline arteriovenous malformations: surgical strategy, techniques, and outcomes. J Neurosurg.
2011;114:984-993.
2. Spetzler RF, Martin NA. A proposed grading system for arteriovenous malformations. J Neurosurg. 1986;65:476-483.
3. Lawton MT, Kim H, McCulloch CE, Mikhak B, Young WL. A supplementary grading scale for selecting patients with brain arteriovenous malformations
for surgery. Neurosurgery. 2010;66:702-713.
4. Zaidi HA, Chowdhry SA, Nakaji P, Abla AA, Spetzler RF. Contralateral interhemispheric approach to deep-seated cavernous malformations: surgical considerations and clinical outcomes in 31 consecutive cases. Neurosurgery. 2014;75:80-86.
5. Rangel-Castilla L, Spetzler RF. The 6 thalamic regions: surgical approaches
to thalamic cavernous malformations, operative results, and clinical outcomes. J
Neurosurg. 2015;123:676-685.
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6. Bohnstedt BN, Kulwin CG, Shah MV, Cohen-Gadol AA. Posterior interhemispheric transfalcine transprecuneus approach for microsurgical resection of periatrial
lesions: indications, technique, and outcomes. J Neurosurg. 2015;123:1045-1054.
7. Lawton MT, Golfinos JG, Spetzler RF. The contralateral transcallosal approach:
experience with 32 patients. Neurosurgery. 1996;39:729-735.
8. Stein BM. Arteriovenous malformations of the medial cerebral hemisphere and the
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COMMENTS
T
he first CNS practical clinic, held in Baltimore, Maryland in October
1987, lasted 8 hours.1 The topic? Surgical positioning. Somewhere
along the way, surgical positioning as a topic lost its sex appeal, but it
remains an unsung, critical step in the planning of a procedure. It is the
first step of performing an operation, and all other phases of a surgery
are affected by it.
In some cases, the patient is positioned in order to optimize the
ergonomics and comfort for the surgeon to reduce fatigue and facilitate
careful microsurgery. I have always emphasized this point to trainees.
In many cases, positioning reduces or eliminates the need for selfretaining retractors, by letting gravity do the work. The authors of this
research have long been proponents of this strategy. The current work
emphasizes the degree of nuance that can go into surgical positioning.
Lateral positioning with gravity retraction of the cerebral hemisphere for
interhemispheric approaches, championed by Spetzler and others, made
surgical treatment of deep pathologies near the midline safer and easier. In
this report, the authors highlight a useful corollary to the more traditional
ipsilateral interhemispheric approach, the contralateral anterior interhemispheric approach (CAIA). As the authors point out, this approach
was used in only 6 of 26 cases of medial frontal AVMs. Lesions must be
ideally suited for the advantages of this approach (gravity delivery of the
malformation, more optimal visualization of the most difficult facets of
the AVM) to outweigh the disadvantages (putting 2 hemispheres at risk
for injury, and a less comfortable, less ergonomic surgeon position). It
is the compromised position of the surgeon that is the main drawback
of this approach, in my mind. For long cases and meticulous dissection,
I believe surgeon comfort is paramount. A fully adjustable chair and a
hand rest can help immensely with this goal.
I applaud the authors focus in this research on surgical positioning,
and continued refinement of surgical approaches. While microsurgical
techniques for cerebrovascular disease are mature, that doesn’t mean
they are unable to be improved. There is plenty of room for continued
evolution of techniques in both the microsurgical and endovascular
realms.
Edward Angus McKay Duckworth
Houston, Texas
1. CNS Brochure/Personal communication, Harry van Loveren, MD
T
his small series describes a contralateral interhemispheric approach
for medial frontal AVMs. This article is well written and the conclusions are valid. I have used this same approach for similar pathologies
and agree with their conclusions and description of the benefits of this
approach. A more posterior contralateral interhemispheric approach can
also be used for parietal AVMs and deeper lesions including thalamic
cavernous malformations with the same benefits cited by the authors.
8 | VOLUME 00 | NUMBER 0 | 2017
The positioning of the patient’s head for this approach is critical and
has a number of benefits. The side of the approach is dependent, lateral
and parallel to the floor with the vertex tilted upward, giving the surgeon
an unencumbered view of the falx with gravity assisting in retraction
of the frontal lobe. Once the falx is opened, the pathology is exposed
without the need for any retractors. Since our eyes are oriented horizontally, this position also provides superior horizontal visualization of the
interhemispheric fissure over the vertical visualization one has with the
more traditional supine position of the patient for an interhemispheric
approach.
One potential risk of this approach is that the dependent frontal lobe
falls away from the falx so effectively that draining veins to the superior
sagittal sinus may be put on stretch and become injured or thrombosed.
These veins must be protected and I have routinely covered them with
gelfoam soaked in heparin which will pass through the vein, assist in
maintaining their patency and reduce the risk of venous infarction.
Daniel L. Barrow
Atlanta, Georgia
RESPONSE TO REVIEWER COMMENTS
Reviewer #2:
This is an interesting and well written technical report about the novel
description of a contralateral anterior interhemispheric approach (CAIA)
to resect frontal medial AVMs instead of the classic ipsilateral anterior
interhemispheric approach (IAIA).
In 6 patients out of 26 surgically treated medial frontal AVMS the
CAIA was used and these 6 patients were further analyzed in this
manuscript. The average AVM diameter was 2.3cm and 2 out of 6
patients had a diameter larger than 3cm with mainly low-grade SpetzlerMartin grade (5 patients Spetzler-Martin grade of 2 and 1 patient with
grade 3). Outcome was favorable with no surgical complications and
good mRS <1 at LFU in all cases, respectively.
The authors explain in detail in which scenario a CAIA is useful
from their point of view (AVM with a lateral margin that extends 2cm,
medially located ascending draining veins being obstacles at risk for a
IAIA approach) and why this approach is not recommended in general
(exposure of both hemispheres and risk of surgical manipulation and risk
of injury, surgical corridor is deepened with a crossing trajectory, intraoperative AVM rupture is difficult to control from a contralateral approach)
and applies only for a small selective group of patients.
We agree with the authors that this approach is useful in carefully
selected patients and we recommend this technical report to be
published. However, we were wondering how the authors define
inclusion criteria of the lateral margin of 2cm. Is this based on a calculated analysis of all 26 treated medial frontal AVMs or from a subjective
point of view? It would be also interesting to have more details on the
control group (IAIA) in terms of AVM size, grade and outcome.
Response:
The inclusion criterion - a lateral margin 2 cm off midline - was not
based on a calculated analysis of all medial frontal AVMs, but offered as
an empiric rule of thumb. AVMs that are right on the midline or within
this 2 cm limit can be easily dissected free and mobilized into the interhemispheric fissure and do not require the steep crossing trajectory of a
contralateral approach. We subjectively decided that the advantages of
the CAIA were not needed for these smaller midline AVMs and were
outweighed by the disadvantages and risks of the CAIA.
www.operativeneurosurgery-online.com
CONTRALATERAL ANTERIOR INTERHEMISPHERIC APPROACH FOR MEDIAL FRONTAL AVMS
Details and surgical results from patients undergoing IAIA were
published previously as part of a larger group of midline AVMs (Kim YB,
Young WL, Lawton MT, for the UCSF BAVM Study Project: Parafalcine
and midline arteriovenous malformations: Surgical strategy, techniques,
and outcomes. Journal of Neurosurgery: 114 (4): 984–993, 2011.) This
group was not meant to be a control group, and it would be difficult
to make meaningful comparisons because the sample sizes in the two
groups are small and there is inherent selection bias in the patients who
underwent CAIA. We included this total number of medial frontal AVMs
only to provide some context for the patients treated with the CAIA, and
we do not think that a review of these IAIA patients would add meaningfully to our message.
OPERATIVE NEUROSURGERY
Reviewer #3: This is a small series that describes a superior
contralateral interhemispheric approach for medial frontal AVMs. The
article is well written and the conclusions are valid. I have personally
used the sam approach as the authors and agree with their conclusions
and description of the benefits of this approach. The exposure is excellent
after opening the falx and the procedure requires no retraction of the
dependent hemisphere.
Response:
We thank the reviewer for these kind comments and are pleased that
his experience agrees with ours. In response to the reviewer’s comments,
we revised our illustrations to show the incisions in the falx and the effects
of gravity retraction.
VOLUME 00 | NUMBER 0 | 2017 | 9
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