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Despite great advances in image-guided technolo-gies, studying actual brain structures is still one of utmost importance. A detailed study of neu-

roanatomy through dissections in cadavers can provide the best orientation in that regard.18,22,24,25,27,28 The modern microneurosurgical approaches mainly require gyri and sulci orientation.3,10,13,20 With the contribution of surgical anatomical studies on the brain surface, several neurosur-gical approaches can be easily performed today.7,8,11,16,17,23 Despite considerable knowledge of intracranial anatomy, little is known about eloquent brain parts and their bone relationships. Cranial-cerebral relationships, firstly de-scribed in the 19th century by Broca, were reevaluated in this study. Misinterpretation of the gyri and sulci pre- and intraoperatively may increase the complication rates.16,29,30 Identifying the gyri, especially when they are not neigh-

boring the sulci or fissures, which are always persistent in the brain, may be very problematic. Therefore, in this study we especially aimed to highlight the methods to identify the gyri with the guidance of the craniometrical points and sutures.

MethodsTen formalin-fixed adult skulls were obtained. Skulls

with the signs of CNS trauma or disease were excluded. The scalp and cranial muscles were removed. The cranial sutures, lines, and craniometrical points were protected,

Window anatomy for neurosurgical approaches

Laboratory investigationSimel Kendir, m.d.,1 Halil ibraHim acar, m.d.,1 ayHan comert, m.d.,1 mevci ozdemir, m.d.,2 GoKmen KaHiloGullari, m.d.,2 alaittin elHan, d.v.m., PH.d.,1 and HaSan caGlar uGur, m.d., PH.d.2

Departments of 1Anatomy and 2Neurosurgery, Ankara University, Sihhiye, Ankara, Turkey

Object. Knowledge of the cranium projections of the gyral structures is essential to reduce the surgical complica-tions and to perform minimally invasive interventions in daily neurosurgical practice. Thus, in this study the authors aimed to provide detailed information on cranial projections of the eloquent cortical areas.

Methods. Ten formalin-fixed adult human skulls were obtained. Using sutures and craniometrical points, the crania were divided into 8 windows: superior frontal, inferior frontal, superior parietal, inferior parietal, sphenoidal, temporal, superior occipital, and inferior occipital. The projections of the precentral gyrus, postcentral gyrus, inferior frontal gyrus, superior temporal gyrus, transverse temporal gyri, Heschl gyrus, genu and splenium of the corpus cal-losum, supramarginal gyrus, angular gyrus, calcarine sulcus, and sylvian fissure to cranial vault were evaluated.

Results. Three-fourths of the precentral gyrus and postcentral gyrus were in the superior parietal window. The in-ferior frontal gyrus extended to the inferior parietal window in 80%. The 3 important parts of this gyrus were located below the superior temporal line in all hemispheres. The orbital and triangular parts were in the inferior frontal win-dow, and the opercular part was in the inferior parietal window. The superior temporal gyrus was usually located in the inferior parietal and temporal windows, whereas the supramarginal gyrus and angular gyrus were usually located in the superior and inferior parietal windows. The farthest anterior point of the Heschl gyrus was usually located in the inferior parietal window. The mean positions of arachnoid granulations were measured as 3.9 ± 0.39 cm anterior and 7.3 ± 0.51 cm posterior to the bregma.

Conclusions. Given that recognition of the gyral patterns underlying the craniotomies is not always easy, aware-ness of the coordinates and projections of certain gyri according to the craniometric points may considerably contrib-ute to surgical interventions. (DOI: 10.3171/2008.10.JNS08159)

Key WordS      •      gyral anatomy      •      neurosurgical approach       •      sulcal anatomy      •      surgical anatomy      •      window anatomy 

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This article contains some figures that are displayed in color on line but in black and white in the print edition.

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and all the remaining bone tissues were removed with the aid of a high-speed drill (Midas Rex Legend Gold Touch) (Fig. 1). The arachnoid granulations and branches of mid-dle meningeal artery on the dura mater were observed (Fig. 2). Then, the dura mater was removed and the cortical structures were inspected. The procedure disclosed 8 win-dows in each hemisphere: superior frontal, inferior frontal, superior parietal, inferior parietal, sphenoidal, temporal, superior occipital, and inferior occipital windows (Fig. 1). The projections of the precentral gyrus, postcentral gyrus, inferior frontal gyrus, superior temporal gyrus, transverse temporal gyri, Heschl gyrus, genu and splenium of the cor-pus callosum, supramarginal gyrus, angular gyrus, calcar-ine sulcus, and sylvian fissure on the windows were evalu-ated. Because these important cortical areas were located in 5 of the 8 windows when craniotomies were performed, these 5 windows (inferior frontal, superior parietal, inferior parietal, and temporal and superior occipital) were taken into consideration during evaluation. To perform a detailed investigation of the parts of the inferior frontal gyrus, the sulci that separated the parts were used. The locations of the arachnoid granulations through the sagittal sinus were observed. The morphometric measurements were done from the bone to the midgyral point. The measurements were obtained using a measuring tape (precision 0.1 mm), and a standard goniometer (precision 1°) was used for angular measurements. An analysis of the measurements (mean ± SD) was also performed.

Shrinkage of the cerebral hemispheres may occur at the time of fixation. Given that the reference points and the direction of measurements varied according to the gyrus examined, a constant linear correction factor was not used in this study. Thus, the sagittal distances of a gyrus located close to the middle of the cerebrum, such as precentral gyrus, will not be significantly affected by the

shrinkage; however, the distances of the gyrus located far from the middle of the cerebrum, such as the orbital part of inferior frontal gyrus, may be affected more.

ResultsPrecentral Gyrus

The precentral gyrus was located 4.5 cm (right 4.34 ± 1.06 cm, left 4.66 ± 0.91 cm) behind the bregma on the midline (Fig. 3) and coursed laterally and frontally, creating a 59° (right 58.8 ± 5.49°, left 59.2 ± 4.37°) angle with the sagittal suture. Three-fourths of the precentral gyrus was in the superior parietal window. At the lower margin of the inferior parietal window, the gyrus reached

Fig. 1. Photograph showing the exposure of the cranium, cranial sutures (coronal [CS], lambdoid [LS], and squamous [SqS] sutures, and superior temporal line [STL]) and craniometric points (bregma [B], stephanion [S], pterion [P], lambda [L], and asterion [A]) in the cadaver skulls. Craniotomies disclose the following 8 windows on each side: superior frontal (1), inferior frontal (2), sphenoidal (3), superior parietal (4), inferior parietal (5), temporal (6), superior occipital (7), and inferior occipital (8).

Fig. 2. Photograph, superior view, showing the branches of the middle meningeal artery on the dura mater, locations of the arachnoid granula-tions, and their distances. SS = sagittal suture.

Fig. 3. Photograph showing the relationships and distances of the precentral gyrus in the superior and inferior parietal windows with the craniometric points (bregma, stephanion, and pterion) and cranial su-tures (coronal, sagittal, and squamous sutures, and superior temporal line).

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the sylvian fissure. The precentral gyrus extended to the temporal window in some hemispheres (30%). On the lat-eral surface, the gyrus was only 2.5 cm (right 2.46 ± 0.63 cm, left 2.54 ± 0.54 cm) behind the stephanion (Fig. 3). In most cases (80%), the precentral gyrus was a strip that had no connection with other gyri.

Postcentral GyrusThe postcentral gyrus was located 6.5 cm (right 6.50

± 0.68 cm, left 6.50 ± 0.65 cm) behind the bregma on the midline (Fig. 4) and coursed laterally and frontally con-stituting a 62° (right 61.9° ± 4.33, left 62.1 ± 4.38°) angle with the sagittal suture. Three-fourths of the postcentral gyrus was in the superior parietal window. At the lower margin of the inferior parietal window, the gyrus reached to the sylvian fissure. The postcentral gyrus extended to the temporal window in some hemispheres (10%). On the lateral surface, the gyrus was located 4.1 cm (right 4.07 ± 0.52 cm, left 4.13 ± 0.45 cm) behind the stephanion (Fig. 4). In most of the cases (90%), the postcentral gyrus was a strip that had no connection with other gyri.

Inferior Frontal GyrusThe end of the inferior frontal gyrus was noted near

the stephanion, 1.9 cm (right 1.97 ± 1.04 cm, left 0.89 ± 0.54 cm) posterior to the coronal suture (Fig. 5). Although the inferior frontal gyrus extended to the inferior parietal window in 80% of the cases, it extended to the superior parietal window in 20%. In the cases in which the inferior frontal gyrus extended to the superior parietal window, the end of the gyrus was located 0.7 cm (right 0.70 ± 0.14 cm, left 0.70 ± 0.18 cm) above the superior temporal line. In cases in which the inferior frontal gyrus extended to the inferior parietal window, the end of this gyrus was 1.8 cm (right 2.00 ± 0.75, left 1.70 ± 0.58 cm) below this line (Fig. 5). The sylvian fissure and its branches (anterior and

ascending rami) were used to separate the inferior fron-tal gyrus into 3 parts: orbital, triangular, and opercular. The locations of these 3 important parts were below the superior temporal line in all the hemispheres. The orbital and triangular parts were in the inferior frontal window, and the opercular part was in the inferior parietal window (Fig. 5). The triangular part could be seen in the inferior parietal window (left 60%, right 50%) (Fig. 5), and the opercular part could be seen in inferior frontal window (left 30%, right 40%). The triangular part was located 1.9 cm (right 2.34 ± 1.42 cm, left 1.38 ± 0.63 cm) anterior to the coronal suture. The triangular part was located 1.4 cm (right 0.97 ± 0.54 cm, left 1.85 ± 0.79 cm) below the superior temporal line.

Superior Temporal Gyrus, Transverse Temporal Gyri, and Heschl Gyrus

In all hemispheres, the superior temporal gyrus was located in the inferior parietal and temporal windows, ex-cept in 1 hemisphere (5%), in which it was seen in the superior parietal window; the crossing point of this gyrus with the superior temporal line was located 7.9 cm behind the stephanion.

The transverse temporal gyrus constitutes the poste-rior part of the upper surface of the temporal lobe, which is known as the temporal plane. The farthest anterior point of the temporal plane, which was also the anterior boundary of the Heschl gyrus, was usually located in the inferior parietal window. This point was placed on the same vertical line with the beginning point of the ascend-ing ramus of the sylvian fissure and in 1 specimen, the point was located in the temporal window. The posteri-or-most boundary of the transverse temporal gyrus was in the area where the posterior ramus of the sylvian fis-sure curved upward. This point was located in the third quarter of the inferior parietal window in all cases. The

Fig. 4. Photograph showing the relationships and distances of the postcentral gyrus in the superior and inferior parietal windows with the craniometric points (bregma, stephanion, pterion, and lambda) and cranial sutures (coronal, sagittal, and squamous sutures, and superior temporal line).

Fig. 5. Photograph showing the relationships and distances of the angular gyrus (AG), supramarginal gyrus (SMG), and parts of the in-ferior frontal gyrus (orbital [Or], triangular [Tr], and opercular [Op]) with the craniometric points (bregma, stephanion, pterion, lambda, and as-terion) and cranial sutures (coronal, sagittal, squamous, and lambdoid sutures, and the superior temporal line).

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anterior-most point of the temporal plane was found 2.8 cm (right 2.92 ± 0.80 cm, left 2.61 ± 0.80 cm) inferior to the superior temporal line. This point was located 0.8 cm (right 0.62 ± 0.15 cm, left 0.93 ± 0.39 cm) posterior to the coronal suture.

Supramarginal GyrusThe point at which the sylvian fissure ended, which

terminates in the middle of the supramarginal gyrus, was noted in order to evaluate the location of the gyrus. In all the hemispheres, this point was seen in the superior and inferior parietal windows. It was located 6.0 cm (right 6.03 ± 1.49 cm, left 6.04 ± 0.70 cm) in front of the lamb-doid suture. The distance between this point and the sag-ittal suture was 6.7 cm (right 6.83 ± 1.28 cm, left 6.59 ± 1.32 cm) on the lateral surface of the hemisphere (Fig. 5). The crossing point of the sylvian fissure with the superior temporal line was located 6.4 cm (right 6.40 ± 0.83 cm, left 6.39 ± 0.88 cm) behind the stephanion in 12 hemi-crania (right 4, left 8) (Fig. 5). In 80% of the cases, the supramarginal gyrus was seen under the parietal tuber.

Angular GyrusThe end of the superior temporal sulcus, which ter-

minates in the middle of the angular gyrus, was consid-ered to evaluate the location of the gyrus. In all the hemi-spheres, this point was seen in the superior and inferior parietal windows. It was located 4.3 cm (right 4.39 ± 1.21 cm, left 4.16 ± 1.00 cm) in front of the lambdoid suture (Fig. 5). The distance between this point and the sagittal suture was 5.0 cm (right 5.01 ± 1.39 cm, left 5.00 ± 1.42 cm) on the lateral surface of the hemisphere (Fig. 5). The crossing point of superior temporal sulcus with superior temporal line was 8.4 cm (right 8.33 ± 0.55 cm, left 8.45 ± 0.54 cm) behind the stephanion. In 20% of the cases, the angular gyrus was located under the parietal tuber.

Calcarine SulcusThe end of calcarine sulcus on superolateral surface

was observed 4.4 cm (right 4.50 ± 1.02 cm, left 4.30 ± 1.13 cm) inferior and 1.7 cm (right 2.00 ± 0.80 cm, left 1.41 ± 0.64 cm) lateral to the lambda. The turning point of cal-carine sulcus from the superolateral surface to the medial surface was different on the right and left hemispheres. The location of this point was 4.0 cm (right 4.00 ± 0.82 cm, left 3.90 ± 0.76 cm) inferior and 0.7 cm (right 1.01 ± 0.23 cm, left 0.40 ± 0.26 cm) lateral to the lambda.

Arachnoid GranulationsArachnoid granulations were accumulated around

(especially behind) the bregma (Fig. 2). The superficial veins of the hemispheres drained into these granulations. The area comprising these granulations was supplied by the branches of the middle meningeal artery (Fig. 2). In all the skulls, the positions of arachnoid granulations were measured as 3.9 ± 0.39 cm anterior and 7.3 ± 0.51 cm posterior to the bregma (Fig. 2). These structures were located 2.6 cm (right 2.40 ± 0.43 cm, left 2.77 ± 0.33 cm) laterally to the sagittal suture (Fig. 2).

Corpus CallosumThe distance between the nasion and genu of the cor-

pus callosum was measured as 12.6 ± 0.44 cm, and the distance between the nasion and splenium of corpus cal-losum was 19.8 ± 0.82 cm.

DiscussionProper craniotomy of a brain lesion and correct in-

terpretation of the gyral structures under the cranioto-my site is one of the most important steps in successful surgery.1,2,20,25 There are very few persistent sulci in the brain that are always present in every individual. There-fore, identification of gyral structures may not be easy. To identify these structures, the use of bone structures of the cranium may prove to be beneficial. To this end, in our study a window anatomy model was developed.

The linear correction factors of 0.88–0.94 can be de-termined at the usual fixation in ~ 4% formalin.14 How-ever, the measurements refer to a relatively small number of cases. Given that the measurements were obtained af-ter 10% formalin fixation, calculations of absolute linear measurements had to include ~ 0.9 as a shrinkage correc-tion factor in the present study. Since the reference points and the direction of measurements varied according to the gyrus examined, a constant linear correction factor was not used in this study.

A reliable identification of functional cortical ar-eas can be achieved through preoperative cortical map-ping.10,21,26,29 In addition, the combination of the data obtained from neuronavigation systems and functional MR imaging evaluations may provide information on the functional cortical areas.12,15 The integration of sul-cal and functional information of the brain and the im-portance of imaging were described by Jannin et al.6 In another study, Gong et al.4 described some cortical area findings obtained through diffusion weighted MR imag-ing techniques. The MR imaging techniques can also be used for superficial brain lesions in the precentral gyrus, as described by Hattingen et al.5 This study reformatted images for fast and easy determination of the locations of the precentral gyrus and perirolandic lesions. A similar study was reported by Krishnan et al.9 In that study, the authors described the functional MR imaging–integrated neuronavigation for correlation between the cranial lesion and motor cortex, which was one of the objectives of our study. Although we have used MR imaging assistance in surgical practice, the study itself focused on the detec-tion of the important cortical areas by using craniometric points in the skull. This detailed anatomical information may prove useful in finding and interpreting the areas un-der the bone.

The positive contribution of advanced technology to surgical outcome is undeniable. However, it is also an undeniable fact that anatomical knowledge and 3D orien-tation are indispensable for successful surgical outcome. Another indication for the importance of anatomical knowledge is the fact that advanced technology is not al-ways available and applicable.15,16

One end of the precentral and postcentral gyri is in

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the interhemispheric fissure, and the other end is in the sylvian fissure. These gyri project forward with an angle of 60°. Thus, their reflections on the midline are signifi-cantly different from those of the sylvian fissure. Conse-quently, a craniotomy closer to the midline will have a different motor and sensorial cortex orientation from that of a craniotomy closer to the sylvian fissure. The closer the precentral gyrus is to the sylvian fissure, the closer it is to the coronal suture, with the distance reducing to as much as 2.8 cm at the stephanion.

The sylvian fissure is a very important corridor for neurosurgical interventions.13,22,19,20 The anterior and as-cending rami are of great importance in defining the in-ferior frontal gyrus, and the posterior ramus is important in defining the supramarginal gyrus. If the rami of the sylvian fissures are not observed in the craniotomy area preoperatively, the definition of these gyri may be highly challenging. In that case, the presence of inferior frontal, precentral, and postcentral gyri in the area on the supe-rior temporal line (in other words, in the inferior parietal window) should be kept in mind. No sulcal structures ex-ist that will aid in defining the angular and supramarginal gyri. Particularly when the posterior ramus of the sylvian fissure is not observed in the craniotomy area, it is impor-tant to know that the area behind the external ear canal, where the inferior parietal and superior parietal windows merge, is where the supramarginal and angular gyri are located. A wide opening of the sylvian fissure is recom-mended for many neurosurgical interventions. It should be kept in mind that all of the important cortical areas such as the Broca, Wernicke, motor and sensory corti-ces, and Heschl gyrus neighbor the sylvian fissure, and in opening the sylvian fissure, trauma is likely to occur to the pial or vascular structures, which may lead to loss of functions related to these areas.

One point to consider in interventions to the mid-line lesions of the brain is the location of the arachnoid villi.8,27,31 These villi become denser right below the cor-onal suture and nearly 5 cm behind the coronal suture. Because these areas point to the venous drainage areas, the venous drainage of the cortical areas may be dam-aged during craniotomy and dura opening. The genu of the corpus callosum is located nearly in the middle of the nasion-bregma space. Most of the distal anterior cerebral artery aneurysms are found in the genu region.8 Thus, in planning an interhemispheric intervention, it is important that the posterior border of the craniotomy be 1 cm ahead of the coronal suture while clipping any aneurysm locat-ed in this area. This will help refrain from unnecessary hemorrhage and potential venous injuries.

The same should be observed in interventions to the Monro foramen (the interventricular foramen).18 The Mon-ro foramen is always in front of the coronal suture and for pathological entities that are not behind the Monro fora-men, the craniotomy should not exceed the coronal suture. The splenium of the corpus callosum is ~ 10 cm away from the bregma, and this area is located at the level of the inter-hemispheric origin of the postcentral gyrus. Keeping this in mind when handling the pathologies of this area may contribute in defining the postcentral gyrus.

The calcarine sulcus is located 4 cm below the lamb-

da, and because of its proximity to the confluence of si-nuses, it can easily be recognized during surgery. Howev-er, it should be kept in mind that the confluence of sinuses in particular may deviate 2 cm from the midline to the right, and thus, the calcarine sulcus may deviate from the midline on the right.

ConclusionsGiven that recognition of the gyral patterns underly-

ing the craniotomies is not always easy, awareness of the coordinates and projections of certain gyri according to the craniometric points may considerably contribute to surgical intervention.

Disclaimer

The authors report no conflict of interest concerning the mate-rials or methods used in this study or the findings specified in this paper.

Acknowledgments

The authors thank Prof. Dr. S. Tuna Karahan and Prof. Dr. Ibra-him Tekdemir (Department of Anatomy, Ankara University Faculty of Medicine) for their invaluable contributions and Mrs. Safak Ugur for her editorial assistance.

References

1. Ersoy M, Evliyaoglu C, Bozkurt MC, Konuskan B, Tekdemir I, Keskil IS: Epipteric bones in the pterion may be a surgical pitfall. Minim Invasive Neurosurg 46:363–365, 2003

2. Figueiredo EG, Deshmukh V, Nakaji P, Deshmukh P, Crusius MU, Crawford N, et al: An anatomical evaluation of the mini-supraorbital approach and comparison with standard crani ot-omies. Neurosurgery 59:212–220, 2006

3. Germann J, Robbins S, Halsband U, Petrides M: Precentral sulcal complex of the human brain: morphology and statisti-cal probability maps. J Comp Neurol 493:334–356, 2005

4. Gong X, Fang M, Wang J, Sun J, Zhang X, Kwong WH, et al: Three-dimensional reconstruction of brain surface anatomy based on magnetic resonance imaging diffusion-weighted im-aging: a new approach. J Biomed Sci 11:711–716, 2004

5. Hattingen E, Good C, Weidauer S, Herminghaus S, Raab P, Marquardt G, et al: Brain surface reformatted images for fast and easy localization of perirolandic lesions. J Neurosurg 102:302–310, 2005

6. Jannin P, Morandi X, Fleig OJ, Rumeur EL, Toulouse P, Gibaud B, et al: Integration of sulcal and functional information for multimodal neuronavigation. J Neurosurg 96:713–723, 2002

7. Kawashima M, Li X, Rhoton AL, Ulm AJ, Oka H, Fujii K: Surgical approaches to the atrium of the lateral ventricle: mi-crosurgical anatomy. Surg Neurol 65:436–445, 2006

8. Kawashima M, Matsushima T, Sasaki T: Surgical strategy for distal anterior cerebral artery aneurysm: microsurgical anato-my. J Neurosurg 99:517–525, 2003

9. Krishnan R, Raabe A, Hattingen E, Szelenyi A, Yahya H, Hermann E, et al: Functional magnetic resonance ımaging-integrated neuronavigation:correlation between lesion-to-motor cortex distance and outcome. Neurosurgery 55:904–915, 2004

10. Levitt JG, Blanton RE, Smalley S, Thompson PM, Guthrie D, McCracken JT, et al: Cortical sulcal maps in autism. Cereb Cortex 13:728–735, 2003

11. Martins C, Li X, Rhoton AL: Role of the zygomaticofacial foramen in the orbitozygomatic craniotomy: anatomic report. Neurosurgery 53:168–173, 2003

S. Kendir et al.

370 J Neurosurg / Volume 111 / August 2009

12. Maudgil DD, Free SL, Sisodiya SM, Lemieux L, Woermann FG, Fish DR, et al: Identifying homologous anatomical land-marks on reconstructed magnetic resonance images of the hu-man cerebral cortical surface. J Anat 193:559–571, 1998

13. Ochiai T, Grimault S, Scavarda D, Roch G, Hori T, Riviere D, et al: Sulcal pattern and morphology of the superior temporal sulcus. Neuroimage 22:706–719, 2004

14. Quester R, Schröder R: The shrinkage of the human brain stem during formalin fixation and embedding in paraffin. J Neurosci Methods 75:81–89, 1997

15. Quiñones-Hinojosa A, Ojemann SG, Sanai N, Dillon WP, Berger MS: Preoperative correlation of intraoperative cortical mapping with magnetic resonance imaging landmarks to pre-dict localization of the Broca area. J Neurosurg 99:311–318, 2003

16. Reinges MH, Nguyen HH, Krings T, Hütter BO, Rohde V, Gils-bach JM: Course of brain shift during microsurgical resection of supratentorial cerebral lesions: limits of conventional neu-ronavigation. Acta Neurochir (Wien) 146:369–377, 2004

17. Rhoton AL Jr: Aneurysms. Neurosurgery 51:21–58, 200218. Rhoton AL Jr: The lateral and third ventricles. Neurosurgery

51:207–271, 200219. Ribas GC, Ribas EC, Rodrigues CJ: The anterior sylvian point

and the suprasylvian operculum. Neurosurg Focus 18(6B): E2, 2005

20. Ribas GC, Yasuda A, Ribas EC, Nishikuni K, Rodrigues AJ Jr: Surgical anatomy of microneurosurgical sulcal key points. Neurosurgery 59:177–211, 2006

21. Sinha TK, Miga MI, Cash DM, Weil RJ: Intraoperative corti-cal surface characterization using laser range scanning: pre-liminary results. Neurosurgery 59:368–377, 2006

22. Tanriover N, Rhoton AL, Kawashima M, Ulm AJ, Yasuda A: Microsurgical anatomy of the insula and the Sylvian fissure. J Neurosurg 100:891–922, 2004

23. Tubbs RS, O’Neil JT Jr, Key CD, Zarzour JG, Fulghum SB, Kim EJ, et al: Superficial temporal artery as an external land-

mark for deeper-lying brain structures. Clin Anat 20:498–501, 2006

24. Tubbs RS, Salter G, Oakes WJ: Superficial surgical landmarks for the transverse sinus and torcular herophili. J Neurosurg 93:279–281, 2000

25. Ucerler H, Govsa F: Asterion as a surgical surgical landmark for lateral cranial base approaches. J Craniomaxillofac Surg 34:415–420, 2006

26. Ugur HC, Kahilogullari G, Coscarella E, Unlu A, Tekdemir I, Morcos JJ, et al: Arterial vascularization of primary motor cortex (precentral gyrus). Surg Neurol 64:48–52, 2005

27. Ugur HC, Kahilogullari G, Esmer AF, Comert A, Odabasi AB, Tekdemir I, et al: A neurosurgical view of anatomical variations of the distal anterior cerebral artery: an anatomical study. J Neurosurg 104:278–284, 2006

28. Uz A, Ugur HC, Tekdemir I: Is the asterion a reliable land-mark the lateral approach to posterior fossa? J Clin Neurosci 8:146–147, 2001

29. Wen HT, Rhoton AL Jr, Marino R Jr: Gray matter overlying anterior basal temporal sulcus an intraoperative landmark for locating the temporal horn in amygdalohippocampectomies. Neurosurgery 59:221–227, 2006

30. Wolfsberger S, Rössler K, Regatschnig R, Ungersböck K: An-atomical landmarks for image registration in frameless ste-reotactic neuronavigation. Neurosurg Rev 25:68–72, 2002

31. Yaşargil MG, Türe U, Yaşargil DC: Surgical anatomy of supra-tentorial midline lesions. Neurosurg Focus 18(6B):E1, 2005

Manuscript submitted March 19, 2008.Accepted October 22, 2008.Please include this information when citing this paper: pub-

lished online April 10, 2009; DOI: 10.3171/2008.10.JNS08159.Address correspondence to: Hasan Caglar Ugur, M.D., Ph.D.,

De partment of Neurosurgery, Ankara University Faculty of Med-i cine, Ibn-i Sina Hospital, 06100 Sihhiye, Ankara, Turkey. email: hasanugur2001@hotmail.com.