1 summary micron euro surgical sulcal key points

8/8/2019 1 Summary Micron Euro Surgical Sulcal Key Points

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MICRONEUROSURGICAL SULCAL KEY POINTS:SULCI ANATOMY AND APPROACHES TO GYRAL

AND TO DEEP CEREBRAL LESIONS(SUMMARY)

Guilherme C. Ribas, M.D.*

This text is a summary of our laboratory findings and of our neurosurgical observations that

were published in three different articles (1, 2, 3), where our results, discussions and references of

other authors publications are fully mentioned.

While the cisternal and the intraventricular lesions are usually approached through standard

craniotomies and microneurosurgical transfissural routes, the cortical-subcortical and the deep

cerebral lesions initially require the understanding of their anatomical localization and

tridimensionality for the selection of its proper transsulcal or transgyral approach and precise

craniotomy placement.

Although the sulci and the gyri of the brain are easily identified in standard magnetic

ressonance images, their accurate visual transoperative recognition is notoriously difficult because of

their common anatomic variations and their arachnoid, cerebrospinal fluid and vessel coverings. The

useful and practical intraoperative frameless imaging devices recently developed, besides being very

expensive and not available in many centers, obviously should not substitute the anatomic

tridimensional knowledge that every neurosurgeon should have to acquire and to continuously

develop as part of her or his practice.

The development of microneurosurgery definetely established the sulci as the fundamentalanatomic lankmarks of the brain surface, and regarding particularly the sulci and gyri relationships

with the cranial vault, it is surprising that despite the huge knowledge of intracranial microanatomy

developed during the last three decades of the microneurosurgical era, little has been studied and

published about anatomic cranialcerebral correlations. The cranial landmarks pertinent to the main

cortical points used in neurosurgery are still based in the important contributions obtained in this field

during the 19th century, which gave rise to modern neurosurgery by making these procedures more

scientifically oriented and hence less exploratory.

* - Professor of Surgery and Clinical Neuroanatomy Coordinator, Department of Surgery, University of So Paulo Medical School.- Professor of Clinical Neurosurgery, University of Virginia.- Neurosurgeon, Hospital Israelita Albert Einstein, So Paulo, SP, Brazil.


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The microneurosurgical importance of the sulci and their notorious difficulty to be identified

during regular neurosurgical procedures justified the study of previously described and new cranial

cerebral relationships in the light of more recent microanatomic knowledge.

Due to the anatomical variations of the brain sulci we elected to study sulcal and gyral key

points that might have more constant anatomical cranial-cerebral relationships. The essential

microsurgical sulcal and cortical key points to be studied were those constituted by the main sulci

extremities and/or intersections, and by the gyral sites that underlie particularly prominent cranial

points. On the superolateral surface of the brain, besides the central sulcus, the precentral sulcus, the

postcentral sulcus, and the always evident sylvian fissure, the other main sulci are the superior frontal

sulcus, the inferior frontal sulcus, the superior temporal sulcus and the intraparietal sulcus.

Among its main results, this study disclosed that 1) the anterior sylvian point lies underneath

the most anterior portion of the squamous suture, 2) the inferior rolandic point underneath the most

superior portion of the squamous suture, 3) the intersection of the inferior frontal sulcus, or of its

posterior prolongation, with the precentral sulcus, lies underneath the Stephanion, craniometric point

that corresponds to the intersection of the superior temporal line with the coronal suture, 4) the

intersection of the superior frontal sulcus, or of its posterior prolongation, with the precentral sulcus,

lies underneath the cranial point located 1.5 cm posteriorly to the coronal suture and 3 cm lateral to

the sagittal suture, 5) the superior rolandic point lies underneath the cranial point located 5 cm

posterior to the Bregma, 6) the intersection of the intraparietal sulcus, or of its anterior prolongation,with the postcentral sulcus, lies underneath the cranial point located 6 cm anterior to the Lambda and

5 cm lateral to the sagittal suture, 7) the superior point of the parieto-occipital sulcus lies underneath

the angle between each lambdoid and the sagittal suture, 8) the Euryon, craniometric point that

corresponds to the center of the parietal tuberosity, is located over the superior aspect of the

supramarginal gyrus, 9) the posterior point of the superior temporal sulcus lies underneath the cranial

point located 3 cm superiorly to the parietomastoid and squamous sutures meeting point, and 10) the

Opisthocranion, that corresponds to the most prominent point of the occipital bossa, is located just

superiorly to the calcarine fissure distal point, over the cuneus most prominent aspect.

The regular neural and cranial cerebral relationships of the above mentioned points

warrant all these sites to be considered consistent microsurgical cortical key-points, that together with

their corresponding cranial points constitute a neurosurgical anatomic framework that can help in the

understanding of cerebral lesions, and that can be used to orient the placement of supratentorial

craniotomies and to ease the initial transoperative identification of brain sulci and gyri.

With the aid of these key points any intrinsic cerebral lesion can be 1) initially understood

regarding the structure and/or the intracranial space that contains the lesion and 2) have its external

cranial projection estimated based on the position of its most related cortical and sulcal key points and


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their corresponding cranial points. In addition, to propitiate the external projection of the lesion, its

most related sulcal key points will also serve as natural references pertinent to the best transsulcal or

transgyral approach for the target lesion, thus further contributing to the proper placement of the

required craniotomy.

According to our findings, the sulcal key points studied here can be intraoperatively

identified within an interval of up to 2 cm relative to their related cranial points, aided by the fact that

the sulcal key points are usually visually characterized by a certain degree of enlargement of the

subarachnoid space because they generally correspond to an intersection of two sulci. The surgeons

knowledge of the usual shape and most frequent anatomic variations of the main brain sulci helps to

corroborate his or her identification of these sulci, and their key points cisternal aspects can then

enhance their characterization as microsurgical dissection starting points and/or as limiting surgical

boundaries.

Considering the dimensions of the usual craniotomies and the usual cortical exposures that

can be further examined through surgical microscopes, an interval range of up to 2 cm between the

sulcal key points and their related cranial points was considered acceptable for the surgical purposes

of craniotomy placement and the intraoperative visual identification of the sulcal key points. The rare

statistically significant differences between the right and the left sides were all pertinent to differences

of measurements far below this 2-cm margin of error.

Nevertheless, it is important to emphasize that anatomical landmarks should not simplysubstitute stereotactic and navigation systems when avaiable, and that any transoperative anatomic

identification of any eloquent cortical area, even when confirmed by a localizing imaging system,

cannot safely substitute for the aid of transoperative functional or neurophysiological testing because

of possible anatomic functional variations and their possible displacements and/or involvement by

the underlying pathology.


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FIGURE 1. CRANIAL SUTURES AND MAIN MIDLINE MEASUREMENTS The skull and the corticalsurface. A) and B), adult skull with its main sutures and most prominent points. C), their averagedistances and their relationships with the sulci and gyri of the brain. Preauricular depression can beeasily palpated over the posterior aspect of the zygomatic arch just in front of the tragus, and the

meeting point of the parietomastoid suture and squamous suture can usually be palpated as adepression along a vertical line originating at the posterior aspect of the mastoid tip; the superiorprolongation of this vertical line will lead to the Euryon area. Average measurements are from Ribaset al. (2).

Ast: Asterion; Br: Bregma; CoSut: coronal suture; Eu: Euryon; In: Inion; La: Lambda; LaSut: lambdoidsuture; Na: Nasion; OpCr: Opisthocranion; PaMaSut: parietomastoid suture; PreAuDepr: preauriculardepression; Pt: pterion; SagSut: sagittal suture: SqSut: squamous suture; SyF: sylvian fissure; St: Stephanion;STL: superior temporal line.


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FIGURE 2. FRONTOTEMPORAL KEY POINTS AND SUPRASYLVIAN OPERCULUMFrontotemporal key points. A) the frontal and temporal sulci and gyri topography can be estimated through the identification of theanterior sylvian point (ASyP), inferior rolandic point (IRP), and inferior frontal and precentral sulci meeting

point (IFS/PreCS). The anterior sylvian point is characterized by enlargement of the sylvian fissure inferior tothe triangular part (Tr) and anterior to the opercular part (Op) of the inferior frontal gyrus (IFG) and servesparticularly as an appropriate starting point for the sylvian fissure opening. The IRP corresponds to the centralsulcus (CS) inferior extremity projection onto the sylvian fissure and is situated approximately 2 to 3 cmposterior to the anterior sylvian point. The IFS/PreCS indicates the height of the inferior frontal sulcus Oppart and delineates the anterior aspect of the precentral gyrus at the face motor activation area . B) regardingtheir cranialcerebral relationships, the ASy point is located underneath the anterior squamous point, justposterior to the pterion. The IRP is usually located underneath the highest superior squamous point, which isalso indicated by a vertical line originating at the preauricular depression. The IFS/PreCS is located underneaththe St cranial area, which corresponds to the site of intersection of the coronal suture with the superiortemporal line.ASqP: anterior squamous suture point, over ASyP; ASyP: anterior Sylvian point; IFS/PreCS: inferior frontal

and precentral sulci meeting point; IRP: inferior rolandic point; SSqP: superior squamous point, over IRP; St:Stephanion, over IFS/PreCS.

Suprasylvian operculum. C) cadaveric specimen, D) sketch, and E) MRI: constituted 1) by the triangular part ofthe IFG located just superiorly to the ASyP, and usually containing a descending branch of the IFS; and of itsfollowing three U-shaped convolutions respectively comprised by 2) the opercular part of the IFG, which isalways intersected by the inferior part of the precentral sulcus; 3) the subcentral gyrus or rolandic operculumcomposed by the inferior connection of the pre- and postcentral gyri enclosing the inferior part of the centralsulcus; 4) the connection arm between the postcentral and the supramarginal gyri that contains the inferior partof the postcentral sulcus; and finally 5) by the C-shaped convolution constituted by the connection of thesupramarginal and superior temporal gyri that encircles the posterior end of the SyF. The bottoms of the U-shaped convolutions and their related sulci extremities can be situated either superior to the fissure or inside itscleft.

AAR: anterior ascending ramus of SyF; ASCR: anterior subcentral ramus; ASyP: anterior sylvian point; CS:central sulcus; HR: horizontal ramus of SyF; IFS: inferior frontal sulcus; IFS/PreCS: inferior frontal andprecentral sulci meeting point; IRP: inferior rolandic point; PAR: posterior ascending ramus of SyF; PostCS:postcentral sulcus; PreCS: precentral sulcus; PSCR: posterior subcentral ramus; PSyP: posterior sylvian point.


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FIGURE 3. SUPERIOR FRONTAL AND CENTRAL KEY POINTSSuperior frontal point. A) the superiorfrontal and precentral sulci meeting point (SFS/PreCS) characterizes an important sulcal key pointthat delineates the anterior aspect of the precentral gyrus at the hand motor activation area level, thusconstituting the posterior limit of the SFS microsurgical opening; B) the SFS/PreCS is locatedunderneath the cranial site situated 1.5 cm posterior to the coronal suture and 3 cm lateral to thesagittal suture (PCoP). These numbers correspond to safe measures because they still tend to disposethis cranial site anterior to the actual SFS/PreCS level; C) whereas the coronal suture (CoSut) radialcoronal plane is at the level of the foramen of Monro (FM), the SFS/PreCS radial coronal plane isrelated with the floor of the lateral ventricle body and thus with the superior surface of the thalamus.

Br: Bregma; CoSut: coronal suture; CS: central sulcus; FM: foramen of Monro; PCoP, posterior coronalpoint, over SFS/PreCS; SFS/PreCS: superior frontal and precentral sulci meeting point;Th: thalamus.

Superior rolandic point (SRP). D) the SRP corresponds to the central sulcus (CS) andinterhemispheric fissure intersection; and E) is located underneath the cranial site 5 cm posterior tothe Bregma (Br); F) while the SFS/PreCS coronal level is related with the body of the lateral ventricle,the opening of the corpus callosum at the level of the SRP may already lead to the subsplenial pinealregion posterior to the junction of both fornices crura.

Br: Bregma; CS: central sulcus; SFS/PreCS: superior frontal and precentral sulci meeting point; SRP: superiorrolandic point; SSaP: superior sagittal point, over SRP.


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FIGURE 4. P ARIETAL KEY POINTS A) the parietal sulci and gyri topography can be estimatedthrough the identification of the superior rolandic point (SRP) that indicates the position of the

central sulcus (CS) superior aspect; the intraparietal sulcus and postcentral sulcus meeting ortransitional point (IPS/PostCS), which should be identified as the postcentral sulcus point mostparticularly related with the intraparietal sulcus anterior extremity level; the supramarginal gyrus(SMG) most prominent aspect; and the medial extremity of the external occipital fissure thatcorresponds to the most superior extremity of the parieto-occipital sulcus (EOF/POS). B) the SRP islocated underneath the cranial area 5 cm posterior to the Bregma (SSaP: superior sagittal point). TheIPS/PostCS is located underneath the cranial area located 6 cm anterior to the Lambda and 5 cmlateral to the sagittal suture. The SMG is located underneath the Euryon that corresponds to the mostprominent point of the parietal tuberosity, roughly along a vertical line originating at the posterioraspect of the mastoid tip and passing through the parietomastoid suture and squamous suture meetingpoint. The external occipital fissure most medial point, that is equivalent to the most superior point of

the parieto-occipital sulcus (EOF/POS), is located underneath the cranial area that corresponds to theangle between the lambdoid and the sagittal suture (La/Sa). C) the IPS/PostCS key point enables theidentification of the intraparietal sulcus (IPS) and postcentral sulcus (PostCS) and is radiallyparticularly related with the atrium (Atr) at its depth. It is important to stress that the IPS openingposterior to the IPS/PostCS can enlarge the exposure of the ventricular Atr but progressively runsaway from this cavity; the key point for the Atr approach is the IPS/PostCS itself.

Atr: atrium of lateral ventricle; CS: central sulcus; EOF/POS: external occipital fissure most medial point,equivalent to the most superior point of the parieto-occipital sulcus; Eu: Euryon, over SMG; IPP: intraparietalpoint, over IPS/PostCS; IPS/PostCS: intraparietal and poscentral sulci meeting point; La/Sa: angle betweenthe lambdoid and the sagittal sutures, over EOF/POS; SMG: supramarginal gyrus; SPL: superior parietallobule; SRP: superior rolandic point; SSaP: superior sagittal point, over SRP; STS: superior temporal sulcus;

SyF: sylvian fissure.


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FIGURE 5. POSTERIOR TEMPORAL KEY POINT A) the superior temporal sulcus constitutes anappropriate microsurgical corridor to the ventricular inferior horn (IH) and atrium (Atr), and itsposterior segment before its usual distal bifurcation (postSTS) is located posterior and inferior to thedistal aspect of the sylvian fissure. Thus, it is posterior to the insula, to the posterior limb of theinternal capsule, and to the thalamus. B) the postSTS lies underneath the cranial area located 3 cmabove the evident squamous and parietomastoid sutures meeting point (SqS/PaMaS). C) a radially(anteriorly) oriented approach through the opening of the postSTS leads to the Atr.

Atr: atrium of lateral ventricle; IH: inferior horn; postSTS: superior temporal sulcus posterior segment distalextremity; SqS/PaMaS: squamous and parietomastoid sutures meeting point; Th: thalamus; TPP:temporoparietal point located over postSTS.


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FIGURE 6. OCCIPITAL KEY POINTSA) the external fissure most medial point, which correspondsto the most superior point of the parieto-occipital sulcus (EOF/POS), and the most prominent aspectof the cuneus (Cu), which lies just superior to the distal extremity of the calcarine fissure (dCaF),constitute two important occipital key points because they delimit the Cu along the interhemisphericfissure (IHF). B) the EOF/POS lies underneath the cranial site constituted by the angle between thelambdoid and the sagittal sutures (La/Sa), and the dCaF is located underneath the cranial area of theOpisthocranion that corresponds to the most prominent point of the occipital bossa. C) theOpisthocranion and the calcarine fissure (CaF) are roughly at the same level of the cingulate gyrusisthmus (Is) and the splenium (Spl). D) the removal of the Is and of the base of the precuneus(preCu) permits the lateral exposure of the atrium (Atr) from the occipital interhemispheric approach.

Atr: atrium; CaF: calcarine fissure; CiG: cingulate gyrus; CiSMR: cingular sulcus marginal ramius; CS: centralsulcus; Cu: cuneus; dCaF: distal extremity of calcarine fissure; EOF/POS: external occipital fissure mostmedial point, equivalent to the parieto-occipital sulcus most superior point; Is: isthmus of cingulate gyrus;La/Sa: angle between the lambdoid and the sagittal sutures, over EOFm; LiG: lingual gyrus; OpCr:Opisthocranion, over distal calcarine fissure; PaCL: paracentral lobule; PHG: parahippocampal gyrus; POS:parieto-occipital sulcus; PreCu: precuneus; Spl: splenium of corpus callosum.


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FIGURE 7. SUPRAPETROSAL KEY POINTSA) the preauricular depression (PreAuDepr) corresponds to theupper portion of the most posterior aspect of the zygomatic process, which is located just anterior to the tragus

and external acoustic meatus. The Asterion (Ast) is the junction of the parietomastoid, lambdoid, andoccipitomastoid sutures(PaMaSut, LaSut, and OccMaSut, respectively). The point at which the parietomastoidand squamous sutures meet (PaMaSut/SqSutMeetPt) usually feels on palpation like a slight depression; visuallyit appears an obvious indentation due to the usually horizontal placement of the parietomastoid suture(PaMaSut) and to the obvious ascendent position of the posteiror part of the squamous suture (SqSut). B) twobur holesthe preauricular bur hole, located immediately above the preauricular depression (1), and the burhole whose base is located 1 cm above the point at which the parietomastoid and squamous sutures meet (2),delimit the external projection of the petrous portion of the temporal bone (Petrous Bone); hence, the middlefossa floor (Middle Fossa) lies anterior to the first bur hole and the superior surface of the tentorium liesposterior to the second bur hole. The bur hole whose base is located 1 cm above the Asterion (3) usually iscompletely, or at least mostly, supratentorial. The line provided by the external occipital protuberance, thatcorresponds to the Inion (In), and the Asterion (Ast), roughly indicates the position of the transverse sinus and

can be relied on to orient further posterior extensions of supratentorial exposures. C and D) intracranially, thefirst bur hole (1), located just above the preauricular depression, is situated adjacent to the foramen spinosum(ForSpi), and along its coronal plane it is related to the upper third of the clivus and, hence, to the mostanterior aspect of the cerebral peduncle of the brainstem (Midbrain). Along its coronal plane, the second burhole (2), whose base lies 1 cm above the interface of the parietomastoid and the squamous sutures, isparticularly related to the most posterior aspect of the midbrain. Intracranially, these two bur holes delimit themost lateral aspect of the superior surface of the petrous portion of the temporal bone (Petrous Bone) and thelateral aspect of the brainstem (Midbrain). The concave middle fossa floor lies anterior to the first bur hole, andthe superior tentorial surface (Tentorium) lies posterior to the second bur hole. A third bur hole (3), whosebase lies 1 cm above the Asterion, is related to the superior aspect of the transverse sinus (TrSi) and, hence,also to the superior tentorial surface.Ast: Asterion; ForSpi: foramen spinosum; In: Inion; LaSut: lambdoid suture; Midbrain: superior part of the

brainstem; Middle Fossa: concave middle fossa floor; OccMaSut: occipitomastoid suture; PaMaSut:parietomastoid suture; PaMaSut/SqSutMeetPt : parietomastoid and squamous sutures meeting point;Petrous Bone: petrous part of the temporal bone; PreAuDepr: preauricular depression; SigSi: sigmoid sinus;SqSut: squamous suture;Tentorium: superior tentorial surface; TrSi: transverse sinus.


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References

1. Ribas GC, Rodrigues Junior AJ. The suprapetrosal craniotomy.J Neurosurg. 2007;106:1-6.2. Ribas GC, Yasuda A, Ribas EC, Nishikuni K, Rodrigues Junior AJ. Surgical anatomy of

microneurosurgical sulcal key-points.Neurosurgery. 2006;59(ONS Suppl4):ONS-177-ONS-209.

3. Ribas GC, Ribas EC, Rodrigues CJ. The anterior sylvian point and the suprasylvian operculum.Neurosurg Focus. 2005;18(6b):E1-E6.

1 summary micron euro surgical sulcal key points

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