RETROSPECTIVE STUDY OF FACTORS DETERMINING

THE SIDE OF APPROACH FOR ANTERIOR

COMMUNICATING ARTERY ANEURYSM

Submitted for M.Ch Neurosurgery

By

DR. VIHANG KANTILAL SALI

OCTOBER 2016

DEPARTMENT OF NEUROSURGERY

SREE CHITRA TIRUNAL INSTITUTE FOR MEDICAL SCIENCES

& TECHNOLOGY

THIRUVANANTHAPURAM – 695011

RETROSPECTIVE STUDY OF FACTORS DETERMINING

THE SIDE OF APPROACH FOR ANTERIOR

COMMUNICATING ARTERY ANEURYSM

Submitted by : Dr. Vihang Kantilal Sali

Programme : M.Ch Neurosurgery

Month & year of submission : October, 2016

CERTIFICATE

This is to certify that the thesis entitled “Retrospective study of

factors determining the side of approach for anterior communicating

artery aneurysm” is a bonafide work of Dr. Vihang Kantilal Sali and was

conducted in the Department of Neurosurgery, Sree Chitra Tirunal Institute

for Medical Sciences & Technology, Thiruvananthapuram (SCTIMST),

under my guidance and supervision.

Dr. Suresh Nair N.

Professor and Head

Department of Neurosurgery

SCTIMST,

Thiruvananthapuram

DECLARATION

This thesis titled “Retrospective study of factors determining the

side of approach for anterior communicating artery aneurysm” is a

consolidated report based on a bonafide study of the period from January

2012 to December 2015, done by me under the Department of Neurosurgery,

Sree Chitra Tirunal Institute for Medical Sciences & Technology,

Thiruvananthapuram.

This thesis is submitted to SCTIMST in partial fulfillment of rules and

regulations of M.Ch Neurosurgery examination.

Dr. Vihang Kantilal Sali

Department of Neurosurgery,

SCTIMST,

Thiruvananthapuram.

ACKNOWLEDGEMENT

The guidance of Dr. Suresh Nair, Professor and Head of the

Department of Neurosurgery, has been invaluable and I am extremely grateful

and indebted for his contributions and suggestions, which were of invaluable

help during the entire work. He will always be a constant source of inspiration

to me.

I owe a deep sense of gratitude to Dr. Mathew Abraham for his

invaluable advice, encouragement and guidance, without which this work

would not have been possible. His critical remarks, suggestions, helped me in

achieving a high standard of work.

I am deeply indebted to Dr. Easwer H. V., Dr. Krishnakumar K.,

Dr. George Vilanilam, Dr. Jayanand Sudhir, Dr. Prakash Nair and

colleagues and I thank them for their constant encouragement and support.

I am also deeply indebted to Dr. Jaykumar for guiding and helping

me in the statistical analysis.

Last but not the least, I owe a deep sense of gratitude to all my patients

without whom this work would not have been possible.

INDEX

INTRODUCTION 1

AIMS AND OBJECTIVES 4

REVIEW OF LITERATURE 6

MATERIALS AND METHODS 35

OBSERVATION AND RESULTS 41

DISCUSSION 60

CONCLUSIONS 68

BIBLIOGRAPHY 70

ANNEXURES 74

1

INTRODUCTION

2

INTRODUCTION

Anterior communicating artery aneurysm is the most common

aneurysm of anterior circulation aneurysms.9, 24 these aneurysms are the most

complex aneurysm of anterior circulation, because of hemodynamics of the

Acom artery region. Acom aneurysms treated by the various approaches like

interhemispheric, subfrontal, lateral supraorbital and pterional. The pterional

approach is most frequently used for the Acom artery aneurysm.

The detailed analysis of Acom complex shows that factors like A1

dominancy, anatomy of aneurysmal neck with A1 and A2 segment,

perforators and presence of other vascular anomalies required to achieve

precise clipping of the aneurysms.5 The advances in the neuroimaging like

magnetic resonance angiography (MRA), 3D CT angiography and 3D digital

subtraction angiography demonstrate the detailed anatomy around the Acom

complex before surgery1

Decision making regarding the surgical approach is based on A1

dominancy, projection and according to that projections how is the plane of

the both A2 vessels. Yasargil25-studied the projection as a predominant

anatomical factor. Inferiorly projecting aneurysms many a times adhere to the

optic chiasm or nerve. The dissection of the arteries that comprising the Acom

complex, recurrent arteries of heubner, and hypothalamic arteries from the

3

neck of the aneurysm were all considered a source of complication.

Furthermore, the premature rupture before complete dissection of the

dominant A1 leads to bleeding. In these situations proximal control of same

side of the A1 segment is the most important step, and thus the dominant A1

side is better for the approaching the aneurysm.

However, there is no such specific approach for superiorly projecting

Acom aneurysm. These type of aneurysms are buried in the interhemispheric

fissure, and concealing the contralateral A1/A2 junction. These aneurysms

partially embedded in the contralateral gyrus rectus. Thus, craniotomy on the

side of A2 anterior displacement simplifies the securing of ipsilateral

dominant A1.It is difficult to handle an aneurysm behind the ipsilateral A2,

particularly when aneurysm adheres tightly to A2.So it is better to approach

this type of aneurysm on the side of posterior displacement of A2 for

visualizing the Acom complex6.

4

AIMS AND OBJECTIVES

5

AIMS AND OBJECTIVE

The hypothesis to undertake this study is that the surgical outcome

differs depending on the side of projection of the aneurysm. The choice of

side of approach in turn depends on dominant A1 and plane of A2 fork with

respect to aneurysm projection

The purpose is to review the practical anatomy, preoperative planning,

and avoidance of complications in the microsurgical dissection and clipping

of Acom aneurysms.

6

REVIEW OF LITERATURE

7

REVIEW OF LITERATURE

Embryology

In a 40-day-old embryo, an arterial plexus that gives rise to the median

artery of the corpus callosum at the age of 45 days connects the two anterior

cerebral arteries. Afterward this artery regresses or disappears. 21 At the same

time the involution of the arterial plexus leads to the formation of the anterior

communicating artery.

Dunker4 classified three different anatomical patterns of the anterior

communicating artery. Fetal type, in which the anterior communicating

artery is equivalent in diameter to the anterior cerebral artery segment and a

large median callosal artery is present. Transitional type, corresponding to a

smaller anterior communicating artery than the anterior cerebral artery

segment with a small median callosal artery. Adult type, in which the anterior

communicating artery's diameter is less than one-third that of the anterior

cerebral artery segment with the absence of the medial callosal artery or only

persistence of a small protrusion.

The anterior communicating artery is 2 to 3.4 mm in diameter (average

1.5 nun). The diameter is proportional to the disparity in the diameters of the

two Al segments. A classic single anterior communicating artery joins in only

40 to 60 percent of the anterior cerebral arteries. The artery length varies from

8

0.8 to 4. 6 mm. The anterior communicating artery generally lies on the optic

chiasm at the level of the lamina terminalis.

Microsurgical Anatomy 13

The A1 segment begins at the terminal bifurcation of the internal

carotid artery (ICA) and ends at the anterior communicating artery (ACoA)

(Fig.1).

This precommunicating segment is also called the horizontal segment

because of its flat course across the optic tract to the midline. Even though

the A1 segment begins and ends at branch points, the segmental anatomy of

the anterior cerebral artery (ACA) is defined by its curvature and its

relationships to the brain rather than by branch anatomy. The A2 segment, or

postcommunicating segment begins at the Acom and follows the rostrum of

the corpus callosum. The A3 segment, or precallosal segment, curves around

the anterior corpus callosum, following the genu until the artery assumes a

posterior course. The A4 (supracallosal) and A5 (postcallosal) segments

continue over the anterior and posterior halves, respectively, of the body of

the corpus callosum, with the vertical plane of the coronal suture dividing

them. The ACA’s bifurcation into the pericallosal artery (PcaA) and the

callosomarginal artery (CmaA) does not define these distal segments

9

Anterior communicating artery aneurysm dissection identifies 12

arteries: ipsi- and contralateral A1 segments; ipsi- and contralateral A2

segments; the Acom; ipsi- and contralateral recurrent arteries of Heubner;

ipsi- and contralateral orbitofrontal arteries; ipsi- and contralateral

frontopolar arteries; and the collection of Acom perforators. The ipsilateral

A1 segment is identified at the ICA terminus and leads medially and

anteriorly over the optic tract and chiasm to the Acom. On average, eight

medial lenticulostriate arteries originate from the superior surface of the A1

segment and ascend to the anterior perforated substance, subfrontal area,

hypothalamus, anterior commissure, septum pellucidum, and paraolfactory

structures. A1 segments are symmetric in most people (90%), but can be

asymmetric due to hypoplastic or aplastic A1 segments. Despite the

suggestion by angiography, absence or true aplasia of the A1 segment is rare

and a vestige can be found intraoperatively. A1 segment dominance is

relevant to aneurysm formation, dome projection, side of hematoma, side of

surgical approach, and proximal control. Duplicated A1 segments are rare

(2% of patients).

A recurrent artery of Heubner is considered the “medialmost” medial

lenticulostriate artery, defining the inner border of the collection of

perforators along the A1 segment (medial lenticulostriates) and M1 segment

(lateral lenticulostriates). As its name implies, a recurrent artery of Heubner

10

travels back along the A1 segment to supply the head of the caudate nucleus,

the putamen, the outer segment of the globus pallidus, and the anterior limb

of the internal capsule, and its injury can produce contralateral face and arm

weakness and expressive aphasia in the dominant hemisphere. A recurrent

artery of Heubner originates on the lateral wall of the proximal A2 segment

just distal to the ACoA, almost as lateral continuations of the ACoA.

Anatomic variation can shift its origin proximal to the ACoA on the distal A1

segment, or in line with the ACoA at the A1-A2 junction, but a recurrent

artery of Heubner lies within 4 mm of the ACoA in 95% of patients.

Exploiting this relationship in reverse, a recurrent artery of Heubner is a

reliable guide to the ACoA and is particularly useful when A1 segment arcs

superiorly out of view. It drapes over the shoulder of the A1 segment at its

origin and lies superior (60%) or anterior (40%) to the A1 segment as it recurs

laterally. Therefore, a recurrent artery of Heubner is often seen before the A1

segment when the frontal lobe is retracted. The artery can be duplicated in

2% of patients. The ACoA joins the A1 segments as they arrive in the

interhemispheric fissure and completes the anterior circle of Willis. ACoA

diameter is about half that of the A1 segments, but asymmetric A1 segments

increase the ACoA diameter.

Important perforating arteries originate from the ACoA’s superior and

posterior surfaces and ascend to the hypothalamus, median paraolfactory

11

nuclei, genu of corpus callosum, columns of the fornix, septum pellucidum,

and anterior perforated substance. Perforators also originate from the anterior

and inferior aspects of the ACoA and descend to the dorsal optic chiasm.

These perforators prevent trapping or dividing the ACoA. If the anterior circle

of Willis requires interruption, it is safer to divide the A1 segment, as long as

the opposite A1 segment and ACoA are sufficiently large.

Orbitofrontal and frontopolar arteries lie beyond a recurrent artery of

Heubner. The orbitofrontal artery is the first cortical ACA branch, arising

from the anterolateral surface of the A2 segment approximately 5 mm distal

to the ACoA and coursing perpendicularly over the gyrus rectus and olfactory

tract. Its course can be similar to that of a recurrent artery of Heubner, but

distally it drifts away from the A1 segment.

Orbitofrontal artery is larger in caliber than the recurrent artery (2 to 3

mm versus 1 mm). The orbitofrontal artery supplies the gyrus rectus, orbital

gyri (anterior, posterior, medial, and lateral), and olfactory bulb and tract. The

frontopolar artery is the second cortical ACA branch, originating from the A2

segment approximately 14 mm from the ACoA. Rarely, it originates from a

common trunk with the orbitofrontal artery. The frontopolar artery courses

anteriorly in the interhemispheric fissure and supplies the ventromedial

frontal lobes.

12

Fig1. Microsurgical anatomy of Anterior Cerebral artery

Normal variations of Anterior Cerebral artery anatomy13

Three variations in efferent A2 segments can lead to misinterpretations

of aneurysm anatomy: azygos, bihemispheric, and accessory ACA(fig.2)

The azygos or “unpaired” ACA is a single midline artery arising from

the confluence of the A1 segments, and occurs in less than 2% of patients.

Distally, the azygos ACA divides into the PcaA and CmaA with bifurcations,

trifurcations, or quadrifurcations.

The “bihemispheric” ACA is an A2 segment that transmits branches

across the midline to both hemispheres, usually in the presence of a

contralateral A2 segment that is either hypoplastic or terminates early in its

course toward the genu. This anomaly is seen in as many as 12% of patients.

The accessory A2 segment is a third artery originating from the ACoA in

addition to ipsi- and contralateral A2 segments.

13

The accessory ACA varies in caliber from a small remnant of the

median artery of the corpus callosum (MACC), to a hyperplastic trunk

resembling an azygos ACA between two smaller A2 segments. The MACC

originates during embryogenesis (44days) when elongating ACAs coalesce

in the midline to form plexiform anastomoses. The MACC regresses and

disappears as A2 segments mature, but remnants account for the accessory

ACA.

Fig2. Normal variations of anterior cerebral artery

14

Determinants of the approaching side 12

Determining factors include Al predominance, the direction of the A2

fork, the direction of the aneurysm, the size of the aneurysm, and the

multiplicity of aneurysms. The presence of fenestration of the AcomA is an

important factor in determining the side of approach. In cases of acute stage

SAH, determining factors include the distribution оf SAH and ICH.

In the case of small- to large-sized aneurysms directed anteriorly (Fig.

3), the Al dominance should be the most important factor because it is

sometimes difficult to secure the opposite side of Al. But there is no marked

difference in surgical difficulty between the right and left approaches.

Fig 3. Inferiorly and anteriorly projecting aneurysm 7

In the case of aneurysms directed superiorly, the Al is bi laterally

secured before approaching the aneurysm. Therefore, entry into the open part

of the A2 fork (i.e., the side o; A2 facing posteriorly) facilitates clipping (Fig.

4).

15

(a) (b)

Fig 4. Superiorly projecting anuerysm (a) open A2 plane (b) closed A2

plane 7

In the case of aneurysms directed posteroinferiorly and that are located

at the back of the AcomA, entry into the side of the A2 located more anteriorly

is recommended, as if the posterior surface of the A2, especially in cases with

fenestration of the AcomA (Fig.5)

Fig 5. Anuerysm facing posteriorly combined with fenestration of

AcomA 7

16

Giant aneurysms are, as a rule, treated by the approach from the

direction in which early arrival at the aneurysmal neck is accomplished.

Approaching from the side of the dominant Al is generally recommended, but

for such an aneurysm that projects anteriorly, the interhemispheric approach

is recommended. The interhemispheric approach is also recommended in

high-positioned Acom aneurysms. 17

Projections-

Anterior communicating artery aneurysms can project at any angle in

three-dimensional space. Classification of these lesions is based on their

orientation in the true anatomical space using the optic nerves as a rough

anteroposterior axis.

Gary Vanderark et al22 categorized Anterior communicating artery

aneurysms by the direction in which it is projected (measured as straight line

from base to fundus) into:

1. Superior

2. Anterior

3. Inferior

4. Posterior

5. Anterosuperior

6. Posteroinferior

17

7. Anteroinferior

8. Posterosuperior.

Yasargil 25 classified AcomA projections under five groups:

1. l. Anterior

2. Superior

3. Inferior

4. Posterior

5. Complex

Nathal E et al 14, further modified it and classified projection of

aneurysms into

Type 1-Aneurysms located anterior to the bilateral A2 portions of the

ACA

Type 2-Aneurysms located between the bilateral A2 portions of the

ACA

Type 3-Aneurysms located posterior to the bilateral A2 portions of the

ACA

Vincentelli et al 23 in their study of 60 fixed human brains indicated

that all perforating branches followed a posterior direction and formed an

angle with the pericallosal arteries that ranged between 30 and 180.

18

Yasargil 25 considered this to be a predominant anatomical factor.

These authors observed a decrease in positive outcomes and an increase in

the mortality rate among patients with superiorly, posteriorly, and inferiorly

projecting aneurysms. In these latter projections, the dissection of arteries

comprising the AComA complex, recurrent arteries of Heubner, frontopolar

and frontoorbital arteries, and hypothalamic arteries from the neck of the

aneurysm were all considered a source of complication. Conversely, for

aneurysms with anterior projection, these arteries are often avoided.

According to Yasargil 25 different projections are-

Superior projection aneurysms:

Frequently associated with a dominant ipsilateral AI vessel, these

lesions usually do not conceal the opposite optic nerve. This project into the

interhemispheric fissure and the contra lateral AI I A2 junction is concealed

by the aneurysmal fundus. This is the most common direction of the

projection of the aneurysmal fundus and may be partially embedded in

contralateral gyrus rectus. These are generally more easily handled than

aneurysms projecting in other positions. Gyrus rectus resection can be helpful

to mobilize the fundus. If the frontoorbital and frontopolar arteries are

attached to the wall of the aneurysm it can be troublesome.

19

Anterior projection aneurysms:

These types fill the space between the two optic nerves, may remain

within area of lamina terminal and may be attached to dura of anterior wall

of sella turcica over tuberculam. Account for 20 to 25 percent of the

aneurysms. They may become entangle to chiasmatic. Larger aneurysm may

displace aneurysm out of interhemispheric fissure.

Posterior projection aneurysms:

These lesions project both above and below the plane formed by the

two A2 segments and usually conceal the contra lateral A2 take off. Almost

always involve early incision into ipsilateral gyrus rectus to visualize the

anatomical structures. The chiasm is uninvolved. Fenestrated clips may be

helpful for the definitive clipping of the posterior projection anterior

communicating artery aneurysms.

Inferior projection aneurysms:

These projections are considered to be the most difficult to handle. The

hypothalamic arteries are usually attached to anterior wall of these

aneurysms. Fundus may directly project into lamina terminalis cistern. Due

20

to intimate association with the perforating vessels and the difficult angle for

clipping, these lesions are treacherous and almost always require an extensive

gyrus rectus resection to allow complete visualization of the aneurysmal

fundus.

Complex projection:

This aneurysm may project in any or all directions and are typically

quite large with lobulations. By noticing the orientation of the fundus the

surgeon will be alert to the particular problems, which may occur at the time

of surgery. However one thing worth considering and important is that there

is a significant difference between the description of the aneurysm projection

given by the radiologist and that actually found by a surgeon at the time of

the surgery. Inferior or anterior projection aneurysms may become tethered

to the optic chiasm or tuberculam sella. A bulbous inferior or anterior

directing lesion can obscure the surgeon's view of the opposite AI segment.

Retraction of the medial frontal lobe could precipitate a premature rupture of

the aneurysm. A superior pointing aneurysm can become adherent to the A2,

Frontoorbital or frontopolar arteries. Posterior pointing fundus can often

become adherent to the perforating vessels. The surgeon must be aware of the

multilobulated aneurysm. Particularly -troublesome are the aneurysms with a

superior and posterior projection. The surgeon may clip the superior portion

21

of the aneurysm between the two A2 segments thereby obscuring the still

patent posterior portion of the aneurysm.

Type of circulation

Norlen and Barnum 15 drew attention to different patterns of circulation

through the anterior part of circle of Willis in patients with anterior

communicating artery aneurysms stressing their importance for various

surgical procedures. Sengupta16 noted four types of circulation, and

aneurysms were classified accordingly.

Type 1: (Ipsilateral) - In this type, the aneurysm and the distal anterior

cerebral artery filled from one proximal anterior cerebral artery.

1. Right anterior cerebral -anterior communicating artery aneurysms. The

pattern of circulation in these aneurysms may be as follows

a) Right carotid injection fills the aneurysm and both the distal anterior

cerebral arteries.

b) Right carotid injection fills the aneurysm and right distal anterior

cerebral artery.

c) Left carotid injection fills the left distal anterior cerebral artery only.

d) Left carotid injection with right carotid compression fills both distal

anterior cerebral arteries but not the aneurysm.

e) As in d), but the aneurysm fills.

22

.

2. Left anterior cerebral -anterior communicating artery aneurysms. In these

aneurysms the following patterns of circulation are possible

a) Left carotid injection fills the aneurysm and both the distal anterior

cerebral arteries.

b) Left carotid injection fills the aneurysm and the left distal anterior

cerebral artery.

c) Right carotid injection fills the right distal anterior cerebral artery

only.

d) Right carotid injection with left carotid compression fills both distal

anterior cerebral arteries but not the aneurysm.

e) As in d, but the aneurysm fills.

23

Type 2: (Bilateral) - In this type, the aneurysm and both anterior cerebral

arteries till from both carotid injections. This pattern of circulation is often

associated with rudimentary anterior communicating arteries. In fact, both

anterior cerebral arteries may be fused to each other .On the other hand, the

anterior communicating artery may be seen as a prominent structure on the

angiograms. The significance of this analysis is that in this type of circulation

the region of the anterior communicating artery receives good collateral

supply, and the effect of vasospasm is minimal. In cases of rudimentary

anterior communicating arteries, however, application of a clip may lead to

kinking of both anterior cerebral arteries, leading to severe ischemic

problems.

24

Type3: (Dominant anterior cerebral artery) -In this type, the aneurysm arises

from the axilla of the two distal anterior cerebral arteries, both of which are

divisions of the dominant anterior cerebral artery, and the contralateral artery

is hypoplastic.

Type 4: (Dominant anterior cerebral artery with foetal posterior cerebral

artery)- In this type, the circulatory patterns are like those in type 3, but there

are other associated anomalies in the circle.

25

■ Aneurysm dissection 13

Anterior communicating artery aneurysms can be approached from

either side. The right side is chosen in patients with symmetric A1 segments,

and the side of the dominant A1 segment is chosen in patients with

asymmetric A1 segments. This policy avoids the speech-dominant

hemisphere in patients with balanced anatomy and exploits advantages of A1

dominance: early proximal control, avoidance, and favorable view of the

neck. Although infrequent in the general population (around 10%), A1

dominance is frequent in the aneurysm population (as high as 80%).

Consequently, the side of approach was even divided in the author’s ACoA

aneurysm experience. With this policy, intraparenchymal hematomas

associated with rupture are typically in the contralateral frontal lobe, but are

contiguous with the aneurysm dome and easily evacuated after clipping.

The side of approach may be influenced by the presence of other lateral

aneurysms that might be treated simultaneously.

26

A standard pterional craniotomy is sufficient for most ACoA

aneurysms, but the orbitozygomatic approach increases exposure for large,

giant, and complex aneurysms (16% in the author’s experience).

Fig 6. Aneurysm Dissection steps

The dissection of ACoA aneurysms proceeds in steps that identify the

five major arteries of the dozen arteries around the ACoA complex, beginning

with the ipsilateral A1 segment step 1), moving to the ipsilateral A2 segment

step 2), and crossing the midline to the contralateral anatomy via the ACoA

step 3). Proximal control of the aneurysm is completed by identifying the

opposite A1 segment (step 4). The contralateral A2 segment is located by

entering the interhemispheric fissure above the aneurysm and distal to the

dome (, step 5). The contralateral A2 segment runs parallel to the ipsilateral

A2 segment and perpendicular to the contralateral orbitofrontal artery, which

can often be seen anteriorly in the interhemispheric fissure. The contralateral

27

A2 segment is traced proximally to the aneurysm neck (Fig. 6 step 6), and

finally the ACoA perforators are dissected from the posterior neck and the

aneurysm is prepared for the clip blade (Fig. 6, step 7).

.

Fig 7. ACom complex and relations with major arteries.

The ACoA complex’s classic position has no lateral rotation, with the

ACoA and both A2 segments lying in a coronal plane (Fig. 7,A,B); extreme

rotation of the complex orients the ACoA and its A2 segments in a sagittal

plane (Fig. 7,C,D). This twisting of the ACoA complex about a vertical axis

shifts the A2 segments and can confuse the dissection. Dominant A1

segments tend to twist the ACoA complex to face the contralateral side in the

direction of blood flow (according to Rhoton’s third rule), bringing the

ipsilateral A2 segment forward and making it easier to identify. However, an

ACoA complex that is twisted toward the side of the approach recesses the

28

ipsilateral A2 segment backward in the fissure and makes it harder to identify.

In addition to this twisting rotation, the horizontal axis of the ACoA complex

can also tilt (Fig. 7, E). An ACoA complex tilted downwards on the side of

approach lowers the ipsilateral A2 segment and brings it into view low in the

interhemispheric fissure; an ACoA complex tilted upwards on the side of

approach raises the ipsilateral A2 segment and often requires gyrus rectus

resection. Tilting and twisting of the ACoA complex also affects the A1

segment. Tilt toward the opposite side elevates the ipsilateral A1 segment and

the superiorly arcing trajectory makes the artery more difficult to visualize.

Fig 8. Dome projections of Acom Aruerysms

The dissection path across the midline to the contralateral A1 and A2

segments is influenced by aneurysm projection. ACoA aneurysms project

anteriorly, posteriorly, inferiorly, or superiorly (Fig.8). In Yasargil’s

experience, superior aneurysms were most common (34%), followed by

29

anterior (23%), posterior (14%), and inferior (13%); multiple lobes or mixed

projection was encountered in 16% of aneurysms.

Dome projection creates a surgical blind spot that conceals a critical

artery or part of the aneurysm. Inferiorly projecting aneurysms hide the

contralateral A1 segment, which limits proximal control. Anteriorly

projecting aneurysms hide the contralateral A1-A2 junction, which hinders

dissection of the distal aneurysm neck. Superiorly projecting aneurysms hide

the contralateral A2 segment. Posteriorly projecting aneurysms hide the

ACoA perforators, which puts them in jeopardy during permanent clipping.

The dissection strategy is determined by the dome projection and this shifting

surgical blind spot. Visible arteries in open surgical corridors are dissected

first, and hidden arteries in the surgical blind spot are dissected last, often

with temporary clipping, aneurysm manipulation, and some de-tethering of

the dome.

30

Fig 9. Dissection steps for inferiroly projecting Acom anuerysms

With inferiorly projecting aneurysms, the contralateral A2 segment

(Fig. 9, step 4) and ACoA (Fig. 9, step 5) are exposed with a superior

dissection path over the aneurysm. The dome hides the contralateral A1

segment, and these aneurysms are sometimes clipped without contralateral

proximal control. Full exposure of the contralateral A1 segment might require

mobilization of the aneurysm and might risk intraoperative rupture. The dome

is also susceptible to avulsion with upward mobilization of the neck when

developing the plane under the neck (Fig. 9, step 6). The contralateral A1

segment and A1-A2 junction are carefully inspected after permanent clipping

if they were not fully exposed before permanent clipping (Fig. 9, step 7)

Fig 10. Dissection steps for superiorly projecting Acom anuerysm

With superiorly projecting aneurysms, the ACoA and contralateral A1

segment are also exposed early with an inferior dissection path (Fig. 10, steps

31

3 and 4). The contralateral A2 segment is hidden behind the aneurysm and

cannot be found simply by ascending into the interhemispheric fissure.

The initial course of the contralateral A2 segment can sometimes be

seen under the belly of the aneurysm, sometimes requiring upward traction

on the aneurysm (Fig. 10, step 5). However, finding the contralateral A2 ACA

requires dissection behind the aneurysm, deep in the interhemispheric fissure

(Fig. 10, step 6). A window is opened behind the ipsilateral A2 segment,

maneuvering the artery and its orbitofrontal and frontopolar branches

anteriorly. Dissection remains above a recurrent artery of Heubner; the space

under it, in its axilla, is narrow, and working there can avulse this delicate

artery. Superior aneurysm projection provides complete proximal control for

temporary clipping and aneurysm softening, which is often needed to

mobilize the aneurysm during this deep dissection. The aneurysm’s posterior

fundus is traversed until the contralateral A2 ACA is identified. With large

aneurysms, it often helps to climb higher in the interhemispheric fissure,

looking for the A2 ACA as it courses beyond the dome. When the

contralateral A2 ACA is found, its inner surface is traced inferiorly, opening

this important cleavage plane down to the origin of the

A2 ACA and distal aneurysm neck. The A2 origin and distal neck are

carefully separated to prepare this spot for the tips of the permanent clip. This

critical anatomy is right in the blind spot of the superiorly projecting

32

aneurysm. Finally, the path way for the posterior clip blade is opened along

the neck above the posterior perforators, being careful not to over dissect

delicate or densely adherent perforators (Fig.10 step 7).

■ Clipping technique 13

At the end of the final dissection, Dome projection influences the

clipping. Inferiorly and anteriorly projecting aneurysms are usually clipped

simply with straight clips. The operative view is along the neck, with afferent

and efferent branches away from the pathway of the clip blades. Inferiorly

projecting aneurysms hide the contralateral A1 segment in the blind spot, and

its exposure may require too much manipulation of a fragile, adherent

aneurysm dome. Therefore, complete proximal control may not be available.

However, the neck of an inferiorly projecting aneurysm is usually well

visualized and an intraoperative rupture can be controlled by simply clipping

the aneurysm. The clip’s tips are inspected safely after permanent clipping;

they must not pass beyond the neck and compromise the contralateral A1

afferent artery. With anteriorly projecting aneurysms, the clip’s tips must not

pass beyond the neck and compromise the origin of contralateral A2 ACA in

the blind spot.

33

Fig 11. Clipping techniques

With superiorly projecting aneurysms, the ipsilateral A2 segment can

interfere with the clip trajectory. A straight clip can be maneuvered around

the ipsilateral A2 segment in the fore field with smaller aneurysms and simple

anatomy (Fig. 9). An anteroposterior clip trajectory, with the clip facing the

front of the aneurysm, avoids the ipsilateral A2 segment. The initial clip

obliterates all the aneurysm behind the A2 segments, and additional under

stacked clips obliterate any remaining aneurysm in front of the A2 segments.

Wide-necked and dolichoectatic aneurysms do not permit this anterior clip

trajectory because clipping often kinks the efferent arteries. Straight

fenestrated clips may be more favorable, with the fenestration encircling the

ipsilateral A2 ACA and the blade paralleling the ACoA (Fig. 10). Fenestrated

clips are also indicated when the cleavage plane between the ipsilateral A2

segment and the proximal neck cannot be opened to pass a blade. Stacked

fenestrated clips build an antegrade fenestration tube that effectively

34

reconstructs the proximal neck without over dissecting this plane, which can

be adherent to thinned aneurysm wall Posteriorly projecting aneurysms are

challenging to clip.

Eleven of the 12 arteries around the ACoA complex are visible in front

of the aneurysm, but the dome projects away from the neurosurgeon and

displaces perforators deep in the interhemispheric fissure. The aneurysm’s

axis is parallel to the line of sight and the neck is behind the ACoA. This

aneurysm geometry and an interposed ACoA complex often require the use

of angled fenestrated clips, which are less maneuverable than straight

fenestrated clips. These clips might encircle the ipsilateral A1 segment,

ipsilateral A2 segment, and/or the ACoA itself, and the view of the perforators

is limited. These concerns are exacerbated by perforators that adhere to the

aneurysm.

35

MATERIALS AND METHODS

36

MATERIALS AND METHODS

Study design and pateints:

Retrospective analysis of 543 cases of all cerebral aneurysms operated

from Jan 2012 to December 2015 was done at Sree Chitra Tirunal Institute

for Medical Sciences and Technology (SCTIMST), Trivandrum. Of these

there were 168 patients had anterior communicating aneurysm.22 cases were

anterior communicating aneurysms with other associated aneurysms. This

study was confined to the 95 of these cases, whose satisfactory diagnostic

preoperative cerebral angiographic films were retrievable from the hospital

data base system as it is mandatory for detailed review.

Study Analysis:

We recorded patient’s demographics, angiographic features of

aneurysms like size, projection, multiplicity, lobulations, dominance of

circulations, plane of A2, and approach related complications. The open A2

plane was defined as when the A2 of the pterional approach side was present

more posteriorly than the contralateral A2.The closed A2 plane was defined

as being present when the ipsilateral A2 was located more anteriorly, because

of this A1-A2 junction and A2 hide the aneurysmal neck.

For SAH patients, we recorded condition at admission by WFNS

scores, severity of hemorrhage by Fisher grade, and day of surgery relative to

37

SAH onset. All patients were evaluated through Glasgow outcome scale at

the time of discharge.

Fig.12 Open and Closed A2plane 19

Operative details

All patients’ were approached through pterional approach operative

details including evidence of SAH, intraoperative rupture, perforator injury,

gyrus rectus aspiration, temporary clipping time was recorded from the

operation records. The effectiveness of the approach was evaluated.

Open A2 plane Closed A2 plane

Open A2 plane Closed A2 plane

38

Pterional approach

Position: patient was positioned supine with bolster under the shoulder

ipsilateral to the aneurysm. Head was fixed to MFK clamp. Head is rotated

15 to 20 degrees away from the side of aneurysm. Head is extended

approximately 20 degree allowing gravity to retract the frontal lobe and

making the malar eminence the high point in surgical field. The head is lifted

above the level of the heart, out of a dependent position. Neck is maintained

in neutral position.

Incision: A curvilinear skin incision begins at zygomatic arch 1cm anterior

to tragus and arcs to the midline, just behind the hairline.

Extracranial dissection: The scalp is elevated to expose the zygomatic root

posterior-inferiorly and the keyhole anteriorly. The superficial fat overlying

the temporalis fascia not entered to preserve the frontalis branch of the facial

nerves. The temporalis muscle is incised from the zygomatic arch to the

superior temporal line along the skin incision, then anterior to the keyhole.

The temporalis muscle is flapped anteriorly, leaving a cuff of fascia and

muscle along the superior temporal line to suture the muscle during closure.

Craniotomy: A fronto-temporal craniotomy was made. The craniotomy

follows the temporalis incision posteriorly, then curves antero-medially to the

foramen of the supraorbital nerve and inferiorly to floor of the anterior cranial

39

fossa. The pterion is located at the intersection of the frontal bone, parietal

bone, and greater wing of the sphenoid bone. It lies at the point where the

coronal sutures intersects with greater wing. The drill was used to remove the

pterion and lesser wing of sphenoid medially to superior orbital fissure, with

the goal of making a flat surface over the orbit connecting the anterior and

middle cranial fossa. The lesser wing is flattened until the lateral edge of the

SOF is reached. Dural fold mobilized laterally by removing bone that forms

the lateral or temporal border of the SOF and base of the clinoid was

rongeured. The squamosal portion of the temporal bone is drilled inferiorly

to the middle fossa floor.

Dural opening:

The dura was opened with semicircular incisions, extending from the

floor of the middle fossa at the posterior-inferior aspect of the exposure to the

floor of the anterior cranial fossa at the anterior-inferior aspect of exposure.

Multiple stay sutures taken.

After opening of dura, sylvian was dissected and operative details were

noted.

40

Statistical analysis: Quantitative Variables were expressed as mean ± sd and

categorical variables were expressed in frequency distribution. Comparison

of quantitative variable between two groups were analyzed by independent

sample t test. Association between categorical variables were analyzed by

Chi-square test. A p-value of 0.05 will be considered as the level of

significant. Data analysis was performed using SPSS version 22.0.

Study limitation:

This study is limited by the inherent drawbacks of a retrospective

analysis. Many of our patients’ data were entered concurrently into

computerized database, we also relied on operative and radiographic reports

as well as other documentation. We were limited by incomplete information

in some patients’ records. Overall we are comfortable with the reliability of

the information that we were able to extract from the medical records, and

took care to note when specific data were insufficient. Only large prospective

study can overcome these weaknesses

41

OBSERVATIONS AND RESULTS

42

OBSERVATIONS AND RESULTS

Among the 95 cases of our study, mean age was 54.2(50-59) years. 63

patients (66.3%) were male patients. There were 88 cases (92.6%) presented

with ruptured aneurysm. Among ruptured aneurysms, 72 (81.8%) were in

grade I and 9(10.2%) were in grade II. The good percentage of preoperative

grade on admission is due to our hospital policy that restricts surgery to

good grade (WFNS grade I-II)

Table 1. Patients demographics:

5.3

27.437.9

29.5

66.3

33.7

81.8

10.24.5 3.4

92.6

0

20

40

60

80

100

< 40 40 - 49 50 - 59 60+ Male Female I II III IV

Age sex WFNS Rupture aneurysms

Patient demography

43

Age

(years)

Frequency Percentage

(%)

< 40 5 5.3

40 - 49 26 27.4

50 - 59 36 37.9

60+ 28 29.5

Sex

Male 63 66.3

Female 32 33.7

WFNS

I 72 81.8

II 9 10.2

III 4 4.5

IV 3 3.4

Ruptured aneurysms 88 92.6

44

Table 2. Pre-operative grading:

CT findings Frequency Percentage

(%)

Fisher's Grade

I 22 26.5

II 13 15.7

III 26 31.3

IV 22 26.5

Gyrus rectus

hematoma 19 20.0

Pre Op infarction 5 5.3

0

5

10

15

20

25

30

35

I II III IV

 Fisher's Grade Gyrushematoma

Pre Opinfarction

Pe

rce

nta

ge

CT findings

45

Table 3. Timing of surgery

Timing of surgery (in

days) Frequency Percentage(%)

1-3 32 33.7

4-7 21 22.1

8-21 33 34.7

>21 9 9.5

Total 95 100.0

For all ruptured aneurysms severity of the hemorrhage was determined

by Fisher grading. Out of 88 cases of ruptured aneurysms, Fisher grade was

grade III in 26(31.3%), and grade IV in 22(26.5%). Gyrus rectus hematoma

was present in 19 patients (20%). 5 patients (5.3%) were presented with

preoperative infarction. The unique referral pattern of our patients is reflected

in the analysis of timing of surgery in relation to the ictus.

46

Table 4. Preoperative imaging analysis:

Angiographic findings Frequency Percent (%)

Size of aneurysm in mm

(mean±sd) 6.3±3.7

AAS 15 15.8

A1 Dominance

Left 57 60.0

Right 26 27.4

No dominance 12 12.6

Multilobulation 19 20.0

Projection

Superior 54 56.8

Inferior 33 34.7

Anterior 6 6.3

Posterior 2 2.1

A2 plane

Open 30 31.6

Closed 65 68.4

47

Among 95 cases whose preoperative Angiographic image analysis

were done to study the aneurysmal morphology. The mean size was

6.3mm.15 patients(15.8%) were presented with other associated aneurysms.

Dominant circulation was present in 72 patients, out of these 57 had left

A1dominace and 26 had rightA1 dominance. Co dominance was present in

12 patients(12.6%). 54 patients had superior projection(56.8%),33 patients

had inferior projection(34.7%).6 patients(6.3%) and 2patients(2.1%) had

anterior and posterior projection respectively. we found 19 cases having

multiple projection due to multiple lobulations and predominant projection

among them was taken as the primary projection. The A2 plane was open in

30 patients (31.6%) and closed in 65 patients (68.4%) at the approach side.

60

27.4

12.620

56.8

34.7

6.32.1

31.6

68.4

15.8

01020304050607080

Left

Rig

ht

No

do

min

ance

Sup

erio

r

Infe

rio

r

An

teri

or

Po

ster

ior

Op

en

Clo

sed

A1 Dominance Multilob Projection A2 plane AAS

Pe

rce

nta

ge

Angiographic findings

48

Table 5. Operative results

Operative findings Frequency Percent

Side of approach

Left 62 65.3

Right 33 34.7

Type

Clip 92 96.8

Wrapping 3 3.2

Intra OP evidence of SAH 77 81.1

IOR 30 31.6

Gyrus rectus aspiration 53 55.8

Perforator injury 3 3.2

Temporary clipping Done 51 53.7

49

Out of 95 patients, 92 Acom aneurysms were clipped and wrapping

done in 3 patients. Intraoperative evidence of SAH was present in 77 patients

(81.1%).Intraoperative ruptured of aneurysms during dissection was present

in 30 patients(31.6%).Perforator injury was occurred in 3

patients(3.2%).Need for gyrus rectus aspiration in 53patients(55.8%).51

patients(53.7%) underwent temporary clipping of dominant A1.The duration

of temporary clipping of dominant A1was 1-20min(mean 6.9min).

0

10

20

30

40

50

60

70

80

90

100

Lef

t

Rig

ht

Cli

p

Wra

ppin

g

Don

e

Side of approach Type Evidence of

SAH

IOR Gyrus rectus

aspi.

Perforator

inj.

TC

Pe

rce

nta

geOperative findings

50

Table 6. Post Operative findings

Post Operative findings Frequency Percentage(%)

Contusion 2 2.1

Major Infarction 11 11.5

Hematoma 11 11.6

CSF diversion 1 1.1

Decompression 5 5.3

Among 95 patients postoperative contusion was seen in 2,infraction

was developed in 29 patients(30.5%). Out of this 11 patients have major

infarct(11.5%). Postoperative hematoma and intraventricular bleed was

present in 11 cases(11.6%), which was resolved on subsequent CT scans,1

patient(1.1%) underwent CSF diversion due to postoperative hydrocephalus

and 5 patients(5.3%) underwent to decompressive craniectomy.

0

2

4

6

8

10

12

Contusion MajorInfarction

Hematoma CSF diversion Decompression

Pe

rce

nta

ge

Post Operative findings

51

Outcome Assessment:

Table 7. Outcome Assessment

GOS Outcome Frequency Percent

Death 4 4.2

Poor 3 3.2

Fair 18 18.9

Good 4 4.2

Excellent 66 69.5

Total 95 100.0

We assessed the Glasgow outcome scale at the time of discharge of 95

patients. Out of these there was mortality in 4 patients (4.2%).Total mortalilty

in operated cases of Acom case was 5% in our study period of Jan2012 to

Dec2015.The excellent outcome was seen in 66 patients (69.5%).

Table 8. A1 dominance projection, A2 plane and side of approach.

4.2% 3.2%

18.9%

4.2%

69.5%

GOS Outcome

Death

Poor

Fair

Good

Excellent

52

Side of approach Total

(N=95) p

Left

(N=62)

Right

(N=33)

N % N % N %

A1

Dominance Left 55 88.7 2 6.1 57 60.0 <0.001

Right 0 0.0 26 78.8 26 27.4

No dominance 7 11.3 5 15.2 12 12.6

Projection Superior 39 62.9 15 45.5 54 56.8 0.418

Inferior 19 30.6 14 42.4 33 34.7

Anterior 3 4.8 3 9.1 6 6.3

Posterior 1 1.6 1 3 2 2.1

A2 plane Open 17 27.4 13 39.4 30 31.6 0.232

Closed 45 72.6 20 60.6 65 68.4

Among 95 patients, A1dominant was present in 83 patients and co –

dominance was present in 12 cases. Out of these left side A1dominance was

present in 57 patient and right dominance in 26 patients. Out of 57 patients of

left dominant- 55 patients had underwent from the left side and 2 had

underwent from the right side. All 26 right dominance patients had underwent

from the right side. The 2 cases which was underwent from the non-dominant

circulation, both were anterio-inferiroly directing aneurysms.

Table 9. Projection of aneurysm and intraoperative complication

53

Projection Total

(N=95) P

Superior

(N=54)

Inferior

(N=33)

Anterior

(N=6)

Posterior

(N=2)

Operative findings N % N % N % N % N %

IOR 18 33.3 10 30.3 1 16.7 1 50 30 31.6 0.793

Intra OP evidence of SAH 42 77.8 27 81.8 6 100 2 100 77 81.1 0.52

Gyrus rectus aspiration 35 64.8 13 39.4 3 50 2 100 53 55.8 0.07

Perforator injury 1 1.9 1 3 0 0 1 50 3 3.2 0.002

Temporary clipping 30 55.6 16 48.5 3 50 2 100 51 53.7 0.533

Table 10. Projection of aneurysm and postoperative complication

Projection

Total

(N=95)

P

Superior

(N=54)

Inferior

(N=33)

Anterior

(N=6)

Posterio

r

(N=2)

Post

Operative

findings

N % N % N % N % N %

Contusions 2 3.7 0 0 0 0 0 0 2 2.1 0.671

Infarction 16 29.6 10 30.3 2 33.3 1 50 29 30.5 0.94

Hematoma 7 13 3 9.1 1 16.7 0 0 11 11.6 0.87

CSF

Diversion 1 1.9 0 0 0 0 0 0 1 1.1 0.857

decompressi

on 4 7.4 1 3 0 0 0 0 5 5.3 0.736

Out of 54 superiorly projecting aneurysms. Intraoperative rupture was

present in the 18 patients (33.3%), Gyrus rectus aspiration was done in the 35

patients (64.9%), 1 patient had the perforator injury. Temporary clipping

applied in 30 cases.16 patients (29.6%) had infarction and 7 patients (13%)

had postoperative hematoma. 2 patients (3.7%) had contusion.4 patients

54

(7.4%) underwent to decompression due to postoperative infract and 1 patient

underwent to CSF diversion due to hydrocephalus.

Out of 33 inferiorly projecting aneurysms, Intraoperative rupture was

present in the 10 patients (30.3%), Gyrus rectus aspiration was done in the 13

patients (39.4%), 1 patient had the perforator injury. Temporary clipping

applied in 16 cases. 10 patients (30.3%) had infraction and 3 patients (9.1%)

had postoperative hematoma.1 patient (7.4%) underwent to decompression

due to postoperative infarct.

Table 11.Projection of aneurysm and Outcome:

Projection Total

(N=95) Superior

(N=54)

Inferior

(N=33)

Anterior

(N=6)

Posterior

(N=2)

Outcome N % N % N % N % N %

death 4 7.4 0 0 0 0 0 0 4 4.2

Poor 2 3.7 1 3 0 0 0 0 3 3.2

Fair 10 18.5 7 21.2 0 0 1 50 18 18.9

Good 3 5.6 1 3 0 0 0 0 4 4.2

Excellent 35 64.8 24 72.7 6 100 1 50 66 69.5

Among superior projecting aneurysms, there were 4 patient (7.4%)

died.35 patients (64.8%) had excellent outcome. Among inferior projecting

aneurysms there were no patient died and excellent outcome came in 24

patients (72.7%).similarly there is no patient died in anterior and posteriorly

projecting aneurysm. But there is no stastical difference in outcome in

different projections.

55

A2 plane and intraoperative and postoperative complications in

superiorly projecting aneurysms

Superior projection cases (N=54)

A2 plane Total

(N=54) p

Open

(N=15)

Closed

(N=39)

N % N % N %

Side of

approach Left 10 66.7 29 74.4 39 72.2 0.572

Right 5 33.3 10 25.6 15 27.8

A1 Dominance Left 9 60.0 25 64.1 34 63.0 0.496

Right 5 33.3 8 20.5 13 24.1

No dominance 1 6.7 6 15.4 7 13.0

Table 12. A2 plane and intraoperative and postoperative complication

in superiorly projecting aneurysms.

56

A2 plane Total

(N=54) p Open

(N=15)

Closed

(N=39)

N % N % N %

IOR 5 33.3 13 33.3 18 33.3 1

Gyrus rectus aspiration 9 60 26 66.7 35 64.8 0.646

Perforator injury 0 0 1 2.6 1 1.9 0.531

Temporary clipping 8 53.3 22 56.4 30 55.6 0.839

Contusion 1 6.7 1 2.6 2 3.7 0.475

Infarction 5 33.3 11 28.2 16 29.6 0.712

Hematoma 2 13.3 5 12.8 7 13 0.96

CSF Diversion 0 0 1 2.6 1 1.9 0.531

DC compression 2 13.3 2 5.1 4 7.4 0.302

Table 13. A2 plane and temporary clipping

A2 plane N

TC

P

Mean SD

Open 8 6.13 4.91 0.32

Closed 22 8.32 5.39

57

Out of 54 superiorly projecting aneurysms, 15 cases had open A2 plane

and 39 had closed A2plane at the operated side. 47 cases showed dominant

circulation and 7 cases there were co-dominance. Out of these dominant

circulation, 33 were present at the closed A2plane and 14 were present at the

open A2 plane.

In these closed A2 plane (n=39), IOR was present in 13 cases (33.3%),

1 case had perforator injury. Postoperative complication like infarction was

present in 11 cases (28.2%), hematoma was present 5 cases (12.8%).1 case

underwent CSF diversion and 2 cases underwent decompressive

hemicraniectomy. In open A2 plane (n=15), IOR was present in 5 cases

(33.3%), No cases had perforator injury. Postoperative infarction was present

6.13

8.32

0

1

2

3

4

5

6

7

8

9

Open Closed

Du

rati

on

in m

inu

tes

Temporary clipping

58

in 5 cases (33.3%), hematoma was present 2 cases (13.3%).2 cases underwent

to decompresive hemicraniectomy.

Thus, there were more surgical and postoperative complications in the

cases of the closed A2plane at approached side. But in all parameters p value

is not significant. The mean duration of the temporary clipping in open plane

was 6.13min and 8.32min in closed plane. (p value=0.32)

Table 14. A2 plane and outcome in superiorly projecting aneurysms

A2 plane Total

(N=54) p

Open

(N=15)

Closed

(N=39)

GOS outcome N % N % N %

death 2 13.3 2 5.1 4 7.4 0.505

Poor 1 6.7 1 2.6 2 3.7

Fair 4 26.7 6 15.4 10 18.5

Good 1 6.7 2 5.1 3 5.6

Excellent 7 46.7 28 71.8 35 64.8

Glasgow outcome scale at time of discharge of superiorly projecting

aneurysm showed the 4 patient (7.4%) mortality.2 patients (5.1%) in closed

A2plane and 2 patients (13.3%) in open A2 plane. Thus in our study there is

no significant statistical difference in outcome between this two group.

59

Inferior Projection Posterior Projection

Superior projection

Closed A2 plane Open A2 plane

Projection and A2 plane of Aneurysm

60

DISCUSSION

61

DISCUSSION

The most important factors of microvascular surgery of Acom

aneurysms is to conceptualize and to clarify the structure in 3Dspace, more

often in superior and anterio-superiorly projecting aneurysm. In such

projections the dome of aneurysm is intimately associated with A2segment

and hiding the Acoma complex and adjacent to critical perforating arteries.

According to Hernesniemi J et al, 8 multiple factors influence the

exposure in ACoAA surgery like rupture status, size, and projection of the

dome the aneurysm, dominance of A1, plane of A2, neurovascular variations,

presence of the associated intraparenchmal and intraventricular hematoma.

Anterior communicating aneurysms more prone to bleed in the frontal

lobe and adjacent ventricular system. The intracerebral hematomas affects the

clinical outcome, so early surgical evacuation is required.

In our study there were 88 cases presented with ruptured aneurysm. 72

(81.8%) were in grade I and 9(10.2%) were in grade II. we had 4(4.5%) and

3(3.4%) patients in grade III and grade IV. The good percentage of

preoperative grade on admission is due to our hospital policy that restricts

surgery to good grade (WFNS grade I-II).

Fisher grading was grade III in 26(31.3%, grade IV in 22(26.5%) and

Gyrus rectus hematoma was present in 19(20%) cases. Dashti et al series

62

reported 30% presented with IVH and it was the second most cause of

aneurysmal ICH that required emergency evacuation.3 Pasqualin et al

16reported ICH with 32% of 402 ruptured ACoAAs.

Operative strategy of the AcoAAs required the detailed review of the

Acoa complex, to preserve the perforators and avoidance of hazardous

premature rupture. Even though the DSA is gold standard in many centers,

multi slice helical CTA is the imaging of choice in our center.

According to review of literature -A1dominance, A2 plane and

projection of aneurysm are the major factors that can decide the operative side

of pterional approaches.

A1 dominance:

One sided dominance can lead to development of AcoA aneurysms.

Cohen and Samson2 reported that 57% of patients with AcoA aneurysm had

A1 dominance. Yasargill 25 found that 80% of patients with AcoA aneurysms

had A1dominance, and explains that an aneurysmal origin from the dominant

A1, and also said that if the A1 supply is equal, the AcoA aneurysm may

originate from the middle of the AcoA complex, suggests hemodynamic

turbulence as predisposing factor. Lawton13 reported 80% frequency of

A1dominance and right sided approach was taken for symmetric A1 and in

asymmetric A1, dominant A1was the criteria to approach the aneurysm.

63

In our study Among 95 patients, A1dominant was present in 83

patients and co –dominance was present in 12 cases. Out of these left side

A1dominance was present in 57 patient and right dominance in 26 pateints.

Out of 57 patients of left dominant- 55 patients had underwent from the left

side and 2 had underwent from the right side. All 26 right dominance patients

had underwent from the right side. The 2 cases which was underwent from

the non-dominant circulation,

According to Hirotoshi Sano, 7 In the case of small- to large-sized

aneurysms directed anteriorly the Al dominance should be the most important

factor because it is sometimes difficult to secure the opposite side of Al. But

there is no marked difference in surgical difficulty between the right and left

approaches.

S-J Hyun et al19 found left A1 dominancy in 78.9% of patients with

superior type compared to 51.5% reported previously. They selected right

side approach in 36.8% and left side in 63.2%.

Suzuki et al 20 said that the inferiorly projecting aneurysm were treated

by A1 dominance and superiorly projecting aneurysm were treated by the A2

plane, they found A1dominance on right side 35.6% and left side 51.1% and

no dominance on 13.3% side of approach was selected according to

A1dominance.

64

Hernesniemi J et al 8 reviewed 921 cases of acom aneurysm and side

selection for pterional approach was A1 dominnace. However, our study

reported no statistical difference between right-sided and left-sided

approaches. Moreover to avoid hazardous intraoperative rupture, care has

been taken to identify which A1 side is dominant when selecting the

approach.24 Therefore, the A1 dominant side is the better Side

Projection: in our study superiorly projecting aneurysms (56.8%) was

the most common followed by the inferior projecting aneurysms

(34.7%).Authors differ in their findings on anterior communicating artery

aneurysm projections. Norlen and Barnum 15 feels that the inferiorly

projecting aneurysms are most common. Yasargil 25 series has posterior

projection as the commonest (34%) followed by superior 22. 7%.

Superior projections frequently associated with a dominant ipsilateral

AI vessel, these lesions usually do not conceal the opposite optic nerve. This

project into the interhemispheric fissure and the contra lateral AI I A2

junction is concealed by the aneurysmal fundus. This is the most common

direction of the projection of the aneurysmal fundus and may be partially

embedded in contralateral gyrus rectus. These are generally more easily

handled than aneurysms projecting in other positions. Gyrus rectus resection

can be helpful to mobilize the fundus. 10

65

Suzuki et al20 suggests Acom projecting inferiorly are easy to clip

without wide dissection of the interhemispheric fissure and preparation of the

bilateral A2 segment, but inferiorly projecting aneurysm more prone to

premature rupture due to adherence to optic chiasm or frontal base. So that

the inferiorly projecting aneurysm were treated by A1 dominance and

conversely in superior projecting aneurysm preparation of bilateral A1

segment is feasible, but key step of neck dissection required detailed

visualization is difficult if same side A1-A2 complex or A2 hides the neck.

Thus superiorly projecting aneurysm were approached by the openA2plane.

Hirotoshi Sano7 suggests in the cases of aneurysms directed

superiorly, the Al is bilaterally secured before approaching the aneurysm.

Therefore, entry into the open part of the A2 fork (i.e., the side of A2 facing

posteriorly) facilitates clipping. In the cases of aneurysms directed

posteroinferiorly and back of neck,entry into the side of the A2 located more

anteriorly is recommended.

Our study there is no statiscal difference in terms of operative strategy

between the different projections.There is no statistical difference in

operative and postoperative complications and outcomes.

Superiorly projecting aneurysm with closed A2plane:

66

Suzuki et al20 showed the higher requirements gyrus rectus aspiration,

higher incidence of residual neck remnant in closed A2 plane (p <0.0001) but

no significant difference in associated vascular injury. There is significant

difference in contusion was observed in patients with closed A2 plane.

(p<0.0092).they consider the open A2 plane is distinct advantage in

approaching the superiorly projecting Acom aneurysms.

S.-J. Hyun et al19 observed, the plane of both A2 vessels was more

important in terms of selecting the approach side than was A1 dominancy.

This indicates that the spatial disposition surrounding ACoA should be

identified before deciding the approach for superior type ACoA aneurysms.

Ten patients (52.6%) were approached from the A2 anterior displacement

side (the closed A2 plane). Of these ten, A1 dominancy was on the right in

two patients (20%) and on the left in eight (80%). The right approach was

selected in three patients (30%), while the remaining seven were treated from

the left (70%). A greater requirement for gyrus aspiration was found for

patients with a closed A2 plane (nine of ten patients, p = 0.041).. However,

no significant relationship was found between the approach side and the

postoperative outcome as evaluated by GOS score.

In our study, there was no significant difference between the open and

closed A2plane in terms of operative, postoperative and outcomes at the time

67

of discharge. More over the evolution in the technique of clipping and use of

fenestrated clips has helped a surgeon to approach from the any side.

68

CONCLUSION

69

CONCLUSION

Our study is exclusively made of the ruptured aneurysm. These

aneurysms need the proximal control, so approaching the Acom aneurysm

from the side of dominance was selected.

On reviewing the literature, surgical approach from the A2 posterior

displacement side (the open A2 plane) in patients with superior projecting

aneurysms allows neurosurgeon to secure aneurysm necks safely and prevent

postoperative complications.

On contrary to this our retrospective study where cases were operated

based on dominant circulation shows no significant relation between open

and closed A2 plane in terms of operative, postoperative complication and

outcomes.

Thus, dominant circulation still be better selection criteria for

approaching the Acom aneurysms to avoidance of hazardous premature

bleeding irrespective of the open and closed A2 plane.

However, this study is limited by the inherent drawbacks of a

retrospective analysis. Many of our patients data were entered concurrently

into computerized database, we also relied on operative and radiographic

70

reports as well as other documentation. We were limited by incomplete

information in some patients records. Only large prospective study can

overcome these drawbacks.

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71

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74

ANNEXURES

ABBREVIATIONS

Acom - Anterior communicating

MRA - Magnetic resonance angiogram

3D - Three dimensional

CT - Computer Tomography

ACOA - Anterior communicating artery

ACA - Anterior cerebral artery

PcaA - Pericallosal Artery

CmaA - Callosomarginal Artery

ICA - Internal cerebral artery

MACC - Median artery of corpus callosum

SAH - Subarachnoid hemorrhage

ICH - Intra cerebral hemorrhage

AAS - Associated aneurysms

WFNS - World Federation of Neurology Society

GOS - Glassgow outcome skill

MFK - May field clamp

SOF - Superior orbital fissure

IOR - intraoperative rupture

GCS - Glassgow coma scale

SD - Standard Deviation

TC - Temporary clipping

IVH - Intra ventricular hemorrhage

DSA - Digital Substraction angiography