Volume 49 - Issue 5.pdf - Minimal Invasive Neurosurgery 2006 - MMikulicz

W.-Y. Cheng

H.-T. Lee

M.-H. Sun

C.-C. Shen

A Pterion Keyhole Approach for the Treatment of

Anterior Circulation Aneurysms

Abstract

comes wider in the deep area, providing sufﬁcient space for

microscope-assisted surgery without the need for highly specia-

lized instruments.

The supraorbital keyhole approach is most frequently used in

treatment for lesions within the anterior cranial base. However,

it has some drawbacks, including cosmetically poor appearance

of the scar, forehead deformity, and difﬁculty in dealing with

some kinds of middle cerebral artery (MCA) and internal carotid

artery (ICA) aneurysms. Therefore, we have developed a small

pterion keyhole approach for an alternative access to treat ante-

rior circulation aneurysms. An oblique skin incision about

3 5 cm in length was made just from 1.0 cm anterior to the

superﬁcial temporal artery at the level of the zygomatic arch,

curved just below the temporal line to the forehead, and stopped

at the hairline over the sylvian ﬁssure. Then a small craniotomy

(2 3 cm) was made just over the sylvian ﬁssure and the aneur-

ysms were exposed through the lateral cerebral ﬁssure. We used

this approach to treat 40 patients with aneurysms located in

posterior communicating arteries (n = 14), the MCA (n = 10), the

anterior communicating arteries (n = 9), the anterior cerebral

artery (n = 1), the ophthalmic arteries (n = 3), and the ICA

(n = 3). The general outcome of all patients was good without

serious complications from the surgical technique even though 3

cases underwent intraoperative premature rupture of the aneu-

rysms. No approach-related complication occurred except that

one patient had vasospasm 2 days after the aneurysm clipping.

In conclusion, this pterion keyhole approach can achieve the best

operative effect for the treatment of intracranial anterior circula-

tion aneurysms in a selective group of patients with several

advantages over traditional craniotomy including minor tissue

damage, less brain retraction, a superior cosmetic result, and

shorter duration of surgery. Moreover, the operative ﬁeld be-

Key words

Intracranial aneurysms keyhole minimally invasive pterion

Introduction

The most deﬁnitive treatment for intracranial aneurysms is

surgical clipping. In most cases, a frontotemporal craniotomy is

required. Although this is tolerated well by most patients, reduc-

ing the size of the opening would be beneﬁcial. Recent advances

in minimally invasive technique and instrumentation permit

certain intracranial aneurysms to be treated using very small

openings. These so-called ‘‘keyhole’’ openings have been used for

exposure of lesions within the anterior cranial base [1–5]. Po-

tential advantages of these approaches include reduced opera-

tive morbidity, expeditious patient recovery, and cost

effectiveness in case management. However, the keyhole ap-

proach is not appropriate for every aneurysm. Only selected

patients can beneﬁt from this innovative approach. The mini-

craniotomy used in these approaches sometimes requires the

use of special instrumentation. In various keyhole procedures,

the supraorbital approach is most frequently applied for the

treatment of supratentorial aneurysms. However, this procedure

has some problems including cosmetically poor appearance of

the scar, forehead deformity, and difﬁculty in dealing some types

257

Afﬁliation

Department of Neurosurgery, Taichung Veterans General Hospital, Taichung, Taiwan, R.O.C.

Correspondence

Chiung-Chyi Shen, M.D. Department of Neurosurgery Taichung Veterans General Hospital 160, Sec. 3,

Taichung-Kang Road Taichung Taiwan Republic of China Tel./Fax: + 886/4/23 74 12 18

E-mail: ns@vghtc.gov.tw

Bibliography

Minim Invas Neurosurg 2006; 49: 257–262 r Georg Thieme Verlag KG Stuttgart New York

DOI 10.1055/s-2006-954575

ISSN 0946-7211

Table 1 Location of aneurysms in 40 patients

Table 2 Hunt and Hess grade and Fisher grade of the patients

(n = 40)

Location of

aneurysm

ICA ACA ACoA PCoA MCA Ophthalmic

artery

Grade

III

Number of

patients

Hunt and Hess

Fisher

–

ICA = internal carotid artery; ACA = anterior cerebral artery; AcoA = anterior

communicating artery; PcoA = posterior communicating artery; MCA = mid-

dle cerebral artery.

of middle cerebral artery (MCA) and internal carotid artery (ICA)

aneurysms. In this article, the authors present an interesting

keyhole approach to treat anterior circulation aneurysms via a

pterion minicraniotomy.

this musculocutaneous ﬂap may conceal a portion of the middle

fossa.

Craniotomy

With a high-speed bone drill, a small burr hole was made at the

temporal bone near the posterior margin of the zygomatic arch

(Fig. 1b). Then a craniotomy was made with a width of 2 3.5 cm

and height of 1.5 2 cm. It was limited by the sphenoid ridge

anteriorly, the suprameatal crest posteriorly, the zygomatic arch

inferiorly, and the squamosal suture superiorly. After craniot-

omy, a groove over the sphenoid ridge of the bone ﬂap was made

and fractured manually to remove the bone ﬂap (Fig. 1c). This

would allow easier control of bleeding from the middle menin-

geal artery. For access to the sylvian ﬁssure, 1 2 cm of the

temporal lobe was exposed by extending the craniotomy to the

ﬂoor of the frontal fossa just above the orbital rim, exposing 2 cm

of the frontal lobe (especially for ACA or ACoA aneurysm), and

retracting the frontal lobe away from the MCA. If the extent of

the frontal fossa exposure was inadequate, it might hamper

visualization up into the sylvian ﬁssure and force the surgeon

to retract the temporal lobe inordinately. A rongeur or a high-

speed drill was then used to remove the bones along the cranial

base, including a portion of the squamous temporal bone and the

sphenoid edge of the greater sphenoid wing. The dura was

opened with an arched fashion around the sylvian ﬁssure,

ﬂapped anteriorly, and tacked over the sphenoid ridge (Fig. 1d).

Oozing from the pterion might be problematic and was usually

reduced with tenting stitches and packing. Spinal drainage, if

needed, was begun as the dura was opened.

Patient and Methods

258

Patients and criteria

From March 1999 to December 2004, we clipped 40 intracranial

aneurysms of the anterior circulation via a pterion keyhole

approach. The aneurysmal locations included 14 posterior com-

municating arteries (PCoA), 10 MCAs, 9 anterior communicating

arteries (ACoA), 1 anterior cerebral artery (ACA), 3 ophthalmic

arteries, and 3 ICAs (Table 1). The patients were selected on the

basis of the following criteria: Hunt and Hess Grades I through

III, and subarachnoid hemorrhage evaluated as Fisher Grades I

through III (Table 2). The patients comprised 24 females and 16

males with an average age of 57.4 years (ranged from 33 to 84

years). Twenty-ﬁve patients presented with subarachnoid he-

morrhage (SAH), of whom twenty received early operation and

ﬁve received delayed operation. Fifteen aneurysms without rup-

ture received a regular operation. For releasing intracranial

pressure and making the minicraniotomy easy, a lumbar drain-

age tube was inserted to drain the cerebrospinal ﬂuid in some

cases. The pterion keyhole approach was performed as we have

previously described [6] and is detailed below.

Head position and skin incision

Under general anesthesia, the patient was placed in a supine

position and immobilized with sandbags. The head was rotated

to the side contralateral to the operative ﬁeld so that the ipsi-

lateral sylvian ﬁssure and sphenoid ridge are oriented vertically.

This rotation usually required turning of the patient’s head by

approximately 30 60 degrees according to the location of the

aneurysm. In addition to rotation, the vertex of the head was

placed downward, allowing the surgeon to see into the sylvian

ﬁssure later. Finally, the head and neck were elevated to improve

venous drainage. The ipsilateral shoulder was elevated with a

cushion beneath to keep the zygomatic arch horizontal. An

oblique skin incision about 3 5 cm in length was made just from

1.0 cm anterior to the superﬁcial temporal artery at the level of

the zygomatic arch, anteriorly curved just below the temporal

line to the forehead, and stopped at the hairline (Fig. 1a). To

expose the skull, the scalp and temporal muscle were incised,

dissected and ﬁxed with elastic retraction. The temporal muscle

near the edge of its insertion to the temporal bone was cut

together with the skin ﬂap. This procedure resulted in excellent

exposure of the anterior and middle cranial base, even though

Although a small portion of the incision extended to the fore-

head, it gave a more excellent cosmetic result than the supraor-

bital keyhole approach and provided sufﬁcient frontal exposure

for visualization deep into the sylvian ﬁssure. This procedure

allows the surgeon to work in the anterior and middle cranial

fossa, the intracranial extradural space, and the subarachnoid

space. Under the microscope, the neurosurgeon could easily gain

a short access to the surgical targets in the suprasellar and

tentorial areas, the circle of Willis, and the whole anterior cranial

base. The pterion keyhole approach has the potential for access

to aneurysms and related structures at the following sites: the

ipsilateral ICA, the medial wall of the contralateral ICA, the ACoA,

bilateral ophthalmic arteries, the M1, M2, and M3 segments of

the ipsilateral MCA, the contralateral PCoA, the anterior choroi-

dal artery, the P1 segment of the PCA, the suprasellar and

tentorial areas, all the anterior cranial base structures, and the

basilar apex. In some selected aneurysm cases, 0- and 30-degree

endoscopic control was used (HSW Co., Tuttlingen, Germany) to

conﬁrm the patency of neighboring perforating arteries, the

PCoA, and the anterior choroidal artery.

Cheng W-Y et al. A Pterion Keyhole Approach ... Minim Invas Neurosurg 2006; 49: 257–262

259

Fig. 1 Surgical procedure of pterion keyhole approach. a The skin incision line was 1.0 cm anterior to the superﬁcial temporal artery at the level

of the zygomatic arch, anteriorly curved just below the temporal line to the forehead, and stopped at the hairline. b A small burr hole was made at

the temporal bone near the posterior margin of the zygomatic arch. c A groove (indicated by arrows) over the sphenoid ridge was made and the

bony ﬂap was removed. d The dura was opened in an arched fashion around the sylvian ﬁssure and turned over anteriorly.

After clipping the aneurysms, the surgical wound was then

closed layer by layer. It was noted that the temporal muscle must

be reattached to the cranium otherwise it might produce a

distinguishable bulge above the zygoma and postoperative fore-

head swelling and ecchymosis.

Table 3 Glasgow outcome scale of the patients (n = 40)

Score

Number of patients

Results

No patient had postoperative visual or retinal disturbances with

regard to either visual acuity or visual ﬁeld impairment.

All of the aneurysms were clipped successfully and uneventfully.

The overall outcome was good (Table 3), except for one patient

who suffered complications of vasospasm and cerebral infarction

2 days after aneurysm clipping. No serious complications and

mortality related to the surgical technique were noted. The

surgical space afforded by use of this approach allows wide

exploration of the anterior fossa, the orbital space, and the

ipsilateral middle fossa structures without limitations. It also

allowed access to portions of the contralateral ICA and its

bifurcation. Three patients showed premature rupture during

dissection of the aneurysmal neck including one each of the

ACoA, PCoA and MCA. However, they were successfully clipped.

All patients sustained transient hypesthesia over the temporal

region, which is expected and acceptable with the use of this

approach and is not considered as a complication. The post-

operative cosmetic result was excellent and the patients were

satisﬁed with it (Fig. 2). After 7 to 50 months of follow-up, we

found that only 3 patients had temporomandibular dysfunction

or signs of atrophy at the site of the craniotomy.

Discussion

Since Yasargil and Fox ﬁrst described the frontotemporal cra-

niotomy with a pterional approach, it has replaced bifrontal and

Cheng W-Y et al. A Pterion Keyhole Approach ... Minim Invas Neurosurg 2006; 49: 257–262

Fig. 2 The case of a right ophthalmic artery

aneurysm treated by the pterion keyhole

approach. a An aneurysm of the right

ophthalmic artery under the microscope.

b Clipping of the aneurysm. c Appearance

of the incision one week after surgery.

d Appearance of the incision two months

after surgery. The cosmetic result was good.

260

frontolateral craniotomies for access to aneurysms of the ante-

rior circulation. A common feature of all these conventional

approaches is the relatively extensive brain exposure and brain

retraction, causing an increase of surgical morbidity not related

to the lesion itself. Occasionally, patients complain of the de-

pressed deformities in the frontotemporal area due to craniot-

omy. Particularly, this occurs as a result of inappropriate repair of

the bone defect at the burr holes. Although application of some

biocompatible materials including hydroxyapatite ceramics [7],

burr-hole buttons and miniplate systems [8, 9] can prevent this

deformity to some extent, it does not ﬁt well to a bone defect at

the keyhole because of the complex curvature of the surrounding

bone.

frontotemporal craniotomy is always visible unless it is made

within the eyebrow. Even for an incisionwithin the eyebrow, hair

loss at the margin of the incision may make it more visible. In

contrast, a scalp incision for a pterion keyhole is entirely behind

the hairline unless the patient is bald. Although any cosmetic

problems caused by burr holes drilled during surgery have been

largely eliminated by the use of plating systems and burr-hole

covers, scalp and cosmetic deformities should be avoided. Ad-

ditionally, the keyhole approach to cerebral aneurysms requires

a slack brain and may be associated with a higher risk of

devastating consequences due to unexpected conditions during

surgery because of the narrower surgical ﬁelds than in a stan-

dard pterional craniotomy. This technique, therefore, is recom-

mended for well-trained neurosurgeons having experience in

conventional craniotomy techniques, because avoidance of brain

injury should be more of a concern to a neurosurgeon than the

length of the skin incision.

Since the implementation of the minimally invasive concept in

neurosurgery is to avoid surgical trauma, many surgical ap-

proaches and technological advances have been made to facil-

itate this goal. The clinical results are overwhelming. Shorter

hospital stay and less morbidity and mortality are achieved with

minimally invasive approaches. Also, minimally invasive ex-

ploration through a small keyhole [10,11] or endoscope-assisted

supraorbital craniotomy [12–14], using an eyebrow or a super-

ciliary skin incision, has become more widely performed with

the improvement of diagnostic imaging and surgical techniques.

Supraorbital keyhole craniotomy seems to cause less injury to

soft tissue and offers excellent cosmetic results compared to the

conventional frontotemporal craniotomy. The skin incision for a

Advantages of the pterion keyhole approach

The pterion keyhole approach offers several advantages com-

pared to a conventional frontotemporal craniotomy. First of all,

brain exposure to air, accidental surgical trauma and brain

retraction is minimal. This signiﬁcantly decreases approach-

related surgical morbidity and shortens hospitalization. Time

spent in the surgical procedure is also signiﬁcantly reduced

when compared to standard techniques. The primary beneﬁt of

the pterion keyhole approach seems to be the avoidance of

Cheng W-Y et al. A Pterion Keyhole Approach ... Minim Invas Neurosurg 2006; 49: 257–262

resection of the orbital rim and roof, and frontal sinus, which

would ultimately lead to a decreased incidence of cerebrospinal

ﬂuid leakage and may result in less cosmetic deformity and less

discomfort than produced by supraorbital or transorbital ap-

proaches. The authors have demonstrated that, in a selected

group of patients, the pterion keyhole approach is a viable

alternative to the traditional pterion approach.

the center of the pterion just over the sylvian ﬁssure. Such an

incision method provided a superior postoperative cosmetic

appearance, because the pterion keyhole was well covered by

the temporal muscle. To avoid damage to the temporal muscle

and the frontal branch of the facial nerve, we cut the temporal

muscle near the edge of its insertion to the temporal bone. This

prevented atrophy of the temporal muscle, temporomandibular

joint problems, indentation of the temple, weakness of the

frontal muscle, eyelid droop, and cosmetic anomalies likely

caused by other cutting methods. Although the pterion keyhole

approach requires a limited skin incision and a small trephinated

bone opening, this approach allowed a short access to the

suprasellar area through the keyhole. Moreover, the operative

ﬁeld became wider as it went deeper. Accordingly, sufﬁcient

operative space was obtained requiring no highly specialized

instruments.

Disadvantages and limitations of the pterion keyhole

approach

Due to the small craniotomy, there is less opportunity to change

the surgical plan if unexpected conditions occur during surgery.

Because brain swelling was difﬁcult to manage with the pterion

keyhole approach, we did not adopt this approach for patients

with severe subarachnoid hemorrhage (Hess and Hunt grades IV

V) without hydrocephalus. Furthermore, an unexpected in-

traoperative serious rupture of the aneurysm would be ex-

tremely difﬁcult to manage under the limited exposure of the

brain by this approach. We prevented this catastrophic event by

adequate exposure of the sylvian ﬁssure and its vascular anat-

omy, as well as CSF drainage. Actually, for each patient, we had

evaluated whether the pterion keyhole approach allowed for

proximal control, dissection of the aneurysm, and application

of the aneurysmal clip in advance. Multidirectional viewing

through the keyhole was only achievable by use of intraoperative

endoscopy. Therefore, preoperative diagnostic imaging is of

paramount importance in reference to the surgical planning

and for preventing the occurrence of unexpected intraoperative

conditions in advance. The pterion keyhole approach for ACoA

aneurysms has drawbacks. A limited resection of the gyrus

rectus is often necessary for adequate control of the AcoA

aneurysms [15].

Application in neurovascular surgery

One of the commonest drawbacks of keyhole approaches in

neurovascular surgery is the risk of bleeding. However, the key-

hole procedures were carefully executed with consideration of

the essential factors regarding aneurysm dissection, including

individual anatomy, proximal vessels (ﬂow control), distal ves-

sels, neck and dome of the aneurysm, and perforating vessels.

Thus, the usual microsurgical space of 20mm at the site of the

lesion is ultimately the same as that required in a large craniot-

omy, without compromising the manipulation of aneurysm

clipping and, especially, without increasing the risk for the

patient. Even though clinoid resection was not necessary for

aneurysms in the paraclinoid segment or carotid cavum in some

of our cases, the above point still works and has been document-

ed in previous experimental studies [5,11,16,17].

261

Surgical ﬂexibility

The pterion keyhole approach is an alternative in the treatment

of patients with anterior circulation aneurysms in a wide ana-

tomic area, either ipsilaterally or contralaterally. One of the

important advantages of the approach is minimal brain retrac-

tion, which is achieved in three ways:

It is possible to gain access to the region of the tip of the basilar

artery with appropriate microdrilling of the posterior clinoid. In

those aneurysms with a ventral neck, a postural change to a more

lateral angle allows better visualization than does the keyhole

supraorbital approach. With regard to the limitation of axial

illumination at 0-degree microscopic visualization, it is also

possible to use an endoscope with 0 and 30 degree optics to

verify the anatomic position of the neighboring arteries, the

PCoA, the anterior choroidal artery, and the perforating arteries

in the supraclinoid segment of the lCA. The procedure is safe

under three-dimensional veriﬁcation of the clip position. A

second placement of the clip was necessary in only three of our

cases.

– changes of the approaching angle when the minicraniotomy

is shifted to the frontal area, allowing access to the bilateral

optic nerves;

– dissection and cistern drainage that is possible at all levels of

the brain and, for approaching the sylvian ﬁssure, is possible

at the pre-pontine cistern; and

– modiﬁcation of the head position with postural support of

gravity permitting access to all of the natural spaces in this

microsurgical corridor.

Improvement of surgical technique

Perneczky and colleagues [1, 5] have advocated the keyhole

concept in neurosurgery and have used the supraorbital mini-

craniotomy extensively for a variety of lesions. Recently, others

have reported experience with this approach in the management

of tumors and aneurysms of the anterior cranial fossa and the

sellar and parasellar regions [2–5].

The pterion keyhole approach allowed for a craniotomy of up to

3.5 cm in diameter, approximately 1.5 cm wider than that ob-

tained using the supraorbital keyhole approach. The larger cra-

niotomy was particularly important because it increased the

ﬁeld of illumination and visualization under the surgical micro-

scope, avoided total reliance on the endoscope, and decreased

the potential obstruction of light by the surgical instruments.

The drawbacks of supraorbital keyhole approach are:

The pterion keyhole approach required a 3- to 5-cm long oblique

skin incision extending from the edge of the zygomatic arch to

– transient loss of supraorbital sensation that frequently oc-

curs and is attributed to traction on the supraorbital nerve;

Cheng W-Y et al. A Pterion Keyhole Approach ... Minim Invas Neurosurg 2006; 49: 257–262

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