Craniometric Points of the Skull and the Cerebral Cortical Surface

3D Neuroanatomymedical atlashttp://www.3dneuroanatomy.com

Craniometric points of the skull and the cerebral corticalsurface

Date : 25 septiembre, 2014

Fernández-Cornejo, V (1); González-López, P (1); Abarca-Olivas, J (1); Méndez-Román, P(1); Moreno-López, P (1); Sanchez del Campo, F (2)

(1) Department of Neurosurgery, Hospital General Universitario de Alicante, Alicante (Spain).(2) Department of Anatomy and Histology, Universidad Miguel Hernández. Campus de SanJuan, Alicante (Spain).

1-INTRODUCTION

The brain sulci and gyri constitutes the main cortical and neuroanatomic limits, landmarks andoperative corridors. The identification of these anatomical structures before and after performingthe craniectomy can help us delimitate the intracraneal lesions and preserve as much aspossible the neurofunctional and eloquent áreas that lies around with the aid of actual and

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modern technology.

It´s difficult to identifying these anatomical structures intraoperatively with precision and thatswhy the main purpose of this study is to establish cortical and sulcal key points of primarymicroneurosurgical importance in order to facilitate the placement of the craniotomies and theidentification of the main brain sulci, thereby providing a sulcal base anatomic framework.

2-FRONTOTEMPORAL KEY POINTS

2a- The Anterior Sylvian Point (ASP)

figure 1.

The anterior Sylvian point (ASP) is a cisternal like enlargement of the Sylvian fissure (SyF).Limits of the ASP: Superior: Pars triangularis; Inferior: superior temporal gyrus (T1); Posterior:Pars opercularis; Anterior: Pars orbitalis. The ASP divides the SyF into an anterior andposterior segment and has a constant location. This anatomic point is the best place to start theopening of the SyF since is the point of maximum separation of the frontal and temporaloperculum. The suprasylvian structures (fronto-parietal operculum) should be imagine as aseries of V and U shape gyri as shown in the picture above. I- The most anterior V shapegyrus corresponds to the Pars triangularis (color orange on figure 1). Anteriorely to this gyrus isthe Pars orbitalis (shown in color red on figure 1). II- Posteriorely to the previous gyrus we canfind a U shape gyrus, the Pars opercularis (colored brown gyrus. figure 1) . This gyrus is limitedposteriorely by the precentral sulcus. Together the pars triangularis and opercularis constitutethe motor speech area of Broca in the dominant hemisphere (Brodmann áreas 44 and 45). III-The next U shape gyrus is called the Subcentral gyrus (Yellow colored on figure 1), alsocalled the "Rolandic operculum" or the classically named “inferior frontoparietal plis de passageof Broca”. Just below and over the Sylvian fissure is situated the inferior Rolandic point (IRP).This gyrus is visible in 95 % of the cases after the dura opening, the other 5 % of the cases ishidden under the superior temporal gyrus. The subcentral gyrus contains the Rolandic centralsulcus and therfore formed by the primary motor and sensitive gyrus. Anterior limit: precentralsulcus; Posterior limit: postcentral sulcus. IV- The third U shaped gyrus (shown on lightblue) is located posteriorely to the postcentral sulcus. Corresponds to the arm shapedgyrus that connects the postcentral and supramarginal gyri. V- The inverted U-shaped gyrus

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(Green figure 1) completes the supramarginal gyrus and it connects inferiorely to the mostposterior part of the superior temporal gyrus. figure 2.

The opening of the SyF at the level of the ASP shows very soon the insular apex on its depth.The Insular limen wich is the point were the middle cerebral artery bifurcatesis located inferiorly and posteriorly (1-2 cm) to the ASP under the depth of T1 and correspondsto the uncinate fasciculus wich connects parts of the limbic system. The opening of the SyFposteriorly to the ASP exposes the insular region and the opening of the SyF anteriorly to theASP leads the surgeon to the suprasellar cisterns. The distance between the ASP and the IRP along the SyF is of arround 2.3 cm (2-2.5 cm). See figure 2. figure 3.

The ASP is related with de external craneal surface at the ANTERIOR SQUAMOUS POINTwich is defined as the point located at the uppermost portion of the junction between theSquamous suture and the sphenoid´s greater wing. (see figure 3).

2b- The Inferior Rolandic Point (IRP)

figure 4.

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The INFERIOR ROLANDIC POINT (IRP) is anatomically situated just below the Rolandiccentral sulcus (CS) just over the SyF. This point is situated 2-2.5 cm posterior to the ASP. TheIRP also corresponds to the anterior limit of the Tranverse gyrus of Heschl or TGH (primaryauditory area), this gyrus is allways "kissing" the postcentral gyrus (primary sensory area). TheTGH on the surface of the superior temporal gyrus corresponds to Wernicke area on thedominat hemisphere wich extends posteriorly to the Angular Gyrus. In other words, the temporallobectomy should never surpass the IRP in order to preserve Wernicke´s area. (figure 4)

figure 5.

The IRP In relation with the cranium, lies at the junction of a vertical line just anterior to thetragus (approximately 4cm above the tragus) and the most superior part of the squamous suture(superior squamous point). Another way to get to the same point (IRP) is to measure 2.5 cmposterior to the Pterion over the squamous suture line as referred by Rhoton Jr. (Figure 5).

2c- The Inferior Frontal Sulcus and Precentral Sulcus Meeting

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point (IFS/PCS)

figure 6

The Inferior Frontal Gyrus (IFS) can be connected or almost connected with the PrecentralSulcus (PCS). This junction point is called The IFS/PreCS meeting point, a practicalneurosurgical key point that can help us localize the precentral gyrus, just posterior and over theprecentral gyrus of this point, correspond specifically to the face motor activation area and alsodelimitates the middle frontal gyrus (F2) from the inferior frontal gyrus (F3 / frontal operculum).See figure 6.

Figure 7.

The Stephanion point is a craniometric point at the level of the intersection between the coronalsuture and the superior temporal line. Normally, the IFS/PreCS meeting point lies around 2 cmposterior to the Stephanions.

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An easy way to delimitate Brocas area on the dominant hemisphere is by localizing the fourcraniometrical points seen on figure 7. a) the Stephanion, b) 2 cm posterior to the StephanionC) the anterior Sylvian point and D) the IRP.

3- THE SUPERIOR FRONTAL AND CENTRAL GYRUS KEYPOINTS

3a-The superior frontal sulcus and precentral sulcus meeting point(SFS/PCS)

figure 8.

The superior frontal sulcus (SFS) is constant and usually a continuous segment and correlateswith the underlying frontal ventricular horn. Considered an important neurosurgicalcorridor. Posteriorly to the union of the SFS with the PreCS correlates to the hand motoractivation area. See figure 8 and 9.

Figure 9.

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The SFS/PCS meeting point is coronally related with the superior surface of the thalamus andwith the body of the lateral ventricle just behind the foramen of Monro.

Figure 10.

The POSTERIOR CORONAL POINT (PCoP) it´s the craniometrical point located 3 cm lateral tothe sagittal suture and 1 cm posterior to the coronal suture, this PCop locates the hand motorcortex underneath the bone, an important neurosurgical landmarc wich must be taken intoaccount in procedures around this area. (Figure 10).

3b-The superior Rolandic point (SRP).

Figure 11.

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The Superior Rolandic Point (SRP) corresponds to the most superior point of the CentralSulcus. Located 5 cm posterior to the bregma. (figure 11). This craniometrical point is used forthe exposure of the precentral and the postcentral gyri.

4- PARIETAL KEY POINTS

4a-The intraparietal and post central sulcus meeting point(IPS/PCS)

Figure 12.

The Intraparietal Sulcus (IPS) can be a continuous or interrupted sulcus on the parietalparenchyma, usually parallel to interhemispheric sulcus and separating the superior from theinferior parietal lobules. The IPS is related anteriorly with the post central sulcus (PCS) andposteriorly it usually continues with the transverse occipital sulcus. (figure 12). It is important to

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locate the IPS/PCS meeting point because: 1- Anteriorly to this point we find the postcentralgurys. 2- It can be use in a neurosurgical procedure as a safe starting point for the transulcal ortranscortical opening. 3- It is related on its depth to the ventricular trigone. Figure 13.

The IPS/PCS craniometrical point is located 6 cm anterior to Lambda and 5 cm lateraly to thesagittal suture. (figure 13).

4b-Craniometrical Key Point of The External Occipital Fissure(EOF)

figure 14.

The external occipital fissure (EOF) corresponds to the extension of the Parieto-Occipital Sulcus(POS) into the brain convexity. It is usually a deep transversal sulcus on the medial side of eachhemisphere. Figure 14.

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Figure 15.

The EOF/POS meeting point is a useful surgical landmark because it defines the parieto-occipital sulcus wich divide de precuneus (parietal) fron the cuneus (occipital) . Figure 15.Figure 16.

This sulcal key point (EOS/POS) lies underneath each paramedian area corresponding to theangle between the sagittal and lambdoid suture. The craniometrical position of Lambda in adultsis around 25 cm posterior to the Nasion, 13 cm posterior to the Bregma and 3 cm superior to theOpisthocranion (not to be confused with the Inion). Figure 16.

figure 17.

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In this picture we can appreciate the POS and Calcarine sulcus wich divide the posterior medialbrain surface in to the Cingularis gyrus (on the precuneus depth), the Precuneus, the Cuneusand Lingualis Giri.

4c-The Euryon (Eu)

Figure 18.

The Euryon or maximal raised point of the parietal tuberosity is located on the junction of thesuperior temporal line (STL) and a vertical line drawn over the most posterior part of the mastoid and through the posterior limit of the squamous suture. (figure 18)

Figure 19.

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The Euryon was found to be over the superior aspect of the supramarginalis gyrus (SMG). TheSMG and Angular Gyrus (AG) belong to the inferior parietal lobule and is separated from thesuperior parietal lobe by the intraparetal sulcus, as you can see on figure 19 and 20.

Figure 20.

The Sulcus that separates the Supramarginalis Gyrus (SMG) and the Angular Gyrus is named"The intermediary sulcus of Jensen" (ISJ) (Figure 20). The ISJ usually continues with the IPS.The SMG is the gyrus found at the most posterior point along the Sylvian fissure and the AG isin the gyrus found at the most posterior point of the superior temporal sulcus (STS). Regardingto the possible surgical complications on parietal approaches, in the dominant hemispherelanguage impairments can be related to the damage of the SMG and AG (Wernickes area).

5- POSTERIOR AND OCCIPITAL POINTS

5a-Posterior temporal key point.

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Figure 21.

Deep in the Superior Temporal Sulcus (STS) we can access to the inferior horn of the lateralventricle. On its posterior third portion the ventricular atrium also can be approached. (Figure21).

Figure 22.

The POSTERIOR TEMPORAL POINT lies normaly unterneath the most posterior portion of thesuperiot temporal gyrus and it is located 3 cm vertically above the meeting point between theparietomastoid suture (figure 22 and 23)

Figure 23.

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The Posterior Temporal Point (PTP) was shown to be 2-3 cm posterior and inferior to theSylvian fissure.

5b-Occipital key point.

Figure 24.

The most prominent occipital cranial point is called "The opisthocranion" (fig.24) Figure 25.

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The opisthocranion is related to the superior aspect of the calcarine fissure and the base of thecuneus. The distance from the opisthocranion to the occipital base or inion is of approximately 2cm and corresponds to the occipital Lingual gyrus (green). The distance from Lambda to theopisthocranion is between 2 and 4 cm and indicates the occipital cuneus (purple). see fig 25.

Figure 26.

Interhemispheric approaches through occipital craniotomies done below the lambda usuallyhave the advantage of dealing with fewer bridging veins than in parietal craniotomies.

6-REFERENCES

R.S. Tubbs, G. Salter, J. Oakes. Superficial surgical landmarks for the transverse sinus andtorcular herophili. J. Neurosurg. 93: 279-281, 2000 S. Gusmao, R. Leal, A. Arantes. Pontosreferencias nos accesos cranianos. Arq Neuropsiquiatr. 2003; 61 (2-A): 305-308. Martinez F., Laxague A., Vida L., et al. Anatomía topográfica del asterion. Neurocirugia 2005; 16: 441-446.Ribas G.C., Ferreira R., Junqueira A. Anaglyfphic three-dimensional stereoscopic printing:revivan of an old method for anatomical and sufical teaching and reporting. J. Neurosurg 95:1057-1066, 2001. Ribas G. C., Ribas E.C., Junqueira C. The anterior sylvian point and thesuprasylvian operculum. Neurosurg Focus 18 (6b), 2005. Kendir S. , Acar H.I., Comert A., et al.

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Window anatomy for neurosurgical approaches. J. Neurosurg. April 10. 2009 Ribas G.C.,Yasuda A., Ribas E.C., Nishikuni K. Surgical Anatomy of microneurosurgical sulcal key points.Neurosurgery 59: ONS 177-210. 2006.

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Craniometric Points of the Skull and the Cerebral Cortical Surface