|Year : 2021 | Volume
| Issue : 2 | Page : 61-65
Morphometry of sylvian fissure among Maharashtrian population
A Shinde Amol1, KA Kushalini2
1 Associate Professor, Department of Anatomy, Dr. D.Y. Patil Vidyapeeth and Medical College, Pune, Maharashtra, India
2 2nd MBBS Student, Dr. D.Y. Patil Vidyapeeth and Medical College, Pune, Maharashtra, India
|Date of Submission||02-Jul-2020|
|Date of Decision||09-Sep-2020|
|Date of Acceptance||18-Mar-2021|
|Date of Web Publication||09-Apr-2021|
A Shinde Amol
B.1004 Westside County Society, Near HP Gas Godown, Pimple Gurav, Pune - 411 061, Maharashtra
Source of Support: None, Conflict of Interest: None
Background: Various studies have documented asymmetry and sexual dimorphism in the Sylvian fissure (SF). The objective of the present study was to determine the morphometry of Sylvian fissure for sexual dimorphism and interhemispherical variations. Methodology: In a descriptive study at Dr. D. Y. Patil Medical College, Pimpri, Pune, Maharashtra, morphometric evaluation of lateral sulcus was done from 50 cerebral hemispheres. SF and Sylvian point with its posterior limb, anterior limb, and ascending limb were demarcated after dissecting out the cerebral hemispheres from the cranial cavity. The length of posterior limb of SF, anterior limb, and ascending limb was noted separately for the left and right sides. The angle between the limbs was noted. Incidence of bifurcation into anterior and ascending limbs as V, U. or Y shape at anterior Sylvian point was noted. Results: The average length of SF (posterior, ascending, and anterior limbs) on the left hemispheres was significantly more than the right side. The length of SF was also significantly more in males in comparison with males. The most common branching pattern of anterior and ascending limbs was U shape (64%). The angle between posterior and ascending limbs on the left side was significantly higher in the left side (104°) than on the right side (98°). Conclusion: Posterior, anterior, and ascending limbs of SF were longer on the left side. Male brains had significantly longer SF than females. U-shaped branching was the most common shape bilaterally and in both sexes. The angle between ascending and anterior limbs was found more in females and on the left side, thus reflecting laterality and sexual dimorphism.
Keywords: Lateral sulcus, pars opercularis, pars triangularis, sexual dimorphism, Sylvian point
|How to cite this article:|
Amol A S, Kushalini K A. Morphometry of sylvian fissure among Maharashtrian population. Natl J Clin Anat 2021;10:61-5
| Introduction|| |
Sylvian fissure (SF) also called lateral sulcus of cerebrum is one of the first sulci to form on the cerebrum., The Broca's speech area and Wernicke's speech association area are located around the SF in the dominant hemisphere. This area is also called perisylvian area and perisylvian language area. In a right-handed person, the left hemisphere is mostly the dominant hemisphere. The SF is located on the lateral surface of cerebral hemisphere, separating the frontal and parietal lobes from the temporal lobe inferiorly. Deep into the fissure, insular cortex is located. The SF divides ventrally at the Sylvian point. It divides into an anterior (anterior inferior) limb and ascending limb. This division is appreciated as V shaped, U shaped, and Y shaped. In Y-shaped division, an ascending stem bifurcates to form anterior and ascending limbs. Posterior limb continues dorsally from the Sylvian point [Figure 1]. The anterior limb separates pars orbitalis below from pars triangularis above, while the ascending ramus separates the pars triangularis anteriorly from pars opercularis posteriorly., As per Brodmann's classification, functional area numbers 45 and 44 are the primary motor speech areas. Areas 44 and 45 are located in the pars triangularis and opercularis, respectively.,
|Figure 1: Lateral surface of left cerebral hemisphere showing A: Posterior limb, B: Ascending limb, and C: Anterior limb, with V-shaped (dotted line) bifurcation|
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Operative approach through SF is used in neurosurgical treatment of temporal lobe epilepsy and lesions in insular cortex and basal ganglia. Pterion approach or frontotemporal sphenoidal craniotomy, SF is exposed. Yasargil has defined four SF configurations based on the frontal and temporal lobe positions at the SF. In the simplest way, SF may be straight and wide (category 1) or straight and narrow (category 2). In cross section, frontal lobe may be protruded into the SF (category 3) or temporal lobe may be protruded (category 4). It is difficult to navigate such configurations during clipping procedures of middle cerebral artery (MCA) aneurysms.
The dot sign denotes the embolic occlusion of branches of MCA in SF. An early warning sign for brain edema and cerebral infarction is hyperdense appearance of main MCA. A positive MCA dot sign is associated with better patient outcome. Mohammad and Niemela state that suprasellar pathologies and MCA and distal basilar artery aneurysms require operation through the SF corridor.
Interhemispherical asymmetry in the anterior part of SF reflects the lateralization of Broca's speech area while the posterior part reflects to lateralization of Wernicke's association area., Loss of asymmetry has been considered as a test of laterality in schizophrenia as per a study by Bartley et al., Rani et al., and Boni et al. reports asymmetry of SF from cadaveric studies done in India and Brazil, respectively. Sexual dimorphism has been seen documented for morphometry of SF by Ide et al. and Liu and Phillips.
Therefore, this study was undertaken among Maharashtrian population with objectives to study the asymmetry of SF for sexual dimorphism and interhemispherical variations.
| Methodology|| |
In a descriptive study at Dr. D. Y. Patil Medical College, Pimpri, Pune, Maharashtra, morphometric evaluation of lateral sulcus was done from 50 cerebral hemispheres. The institutional ethics committee approved the study before the beginning (IESC/C-108/2019). The samples included 19 male brains and 6 female brains.
All adult cerebral hemispheres with no gross damage were included.
Infant or adolescent cerebral hemispheres and hemispheres with damage or any gross morphological variation in the hemisphere were excluded.
Morphometric evaluation of lateral sulcus
After dissecting out the brain from the cranial cavity, the superficial vessels and meningeal coverings were carefully removed from the superolateral surface of cerebral hemispheres. SF and Sylvian point with its posterior limb, anterior limb, and ascending limb were demarcated. The length of posterior limb of SF, anterior limb, and ascending limb was noted separately for the left and right sides. The angle between anterior limb and ascending limb and between posterior limb and ascending limb was noted. Incidence of bifurcation into anterior and ascending limbs as V [Figure 1] or U [Figure 2] shape at anterior Sylvian point was noted. Incidence of formation of a common stem bifurcating at the Sylvian point to form Y shape [Y] [Figure 3] was noted.
|Figure 2: Lateral surface of left cerebral hemisphere showing U-shaped (dotted line) bifurcation of ascending and anterior limbs of lateral sulcus|
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|Figure 3: Lateral surface of right cerebral hemisphere showing Y-shaped (dotted line) bifurcation of ascending and anterior limbs of lateral sulcus|
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All measurements were taken by placing a thread on the surface of the hemisphere and both ends held by forceps. The measurements of the thread length were done by digital Vernier caliper and angles were measured by protractor. Right/left measurements and male/female measurements were noted separately.
All continuous variables were expressed as mean with standard deviations. Differences between right/left and male/female values were determined with Student's t-test. Significance was judged at P < 0.05. The data were computed with MS Excel 2017 software.
| Results|| |
The maximum length of posterior limb is 5.47 cm on the right side and 5.49 cm on the left side [Table 1]. [Figure 4] depicts the average lengths of limbs of lateral sulcus. The maximum length of anterior limb is 2.1 cm on the right side and 2.23 cm on the left side. Ascending limb showed a maximum length of 2.47 cm on the right side and 2.90 cm on the left side. The average length of SF (posterior, ascending, and anterior limbs) on the left hemispheres was significantly more than the right side. The length of SF was also significantly more in males in comparison with females. The most common branching pattern of anterior and ascending limbs was U shape (32 out of 50, 64%). Y-shaped branching was not appreciated among female cerebral hemisphere. Ascending ramus was longer than anterior ramus in 78.9% (30 out of 38) of the male hemispheres and 75% (9 out of 12) of the female hemispheres. Ascending ramus was larger on the right side in 70% of the male hemispheres and in 60% of the female hemispheres.
|Figure 4: Lateral surface of left cerebral hemisphere showing average lengths of anterior, ascending, and posterior limbs of lateral sulcus with angle between anterior and posterior limbs (blue) and angle between ascending and posterior limbs (green)|
Click here to view
The angle between posterior and ascending limbs on the left side was significantly higher in the left side (104°) than on the right side (98°). This indicates a smaller pars opercularis on the left side. The average angle between ascending and anterior rami is 66° on the right side and 72° on the left side. This indicates a larger pars triangularis on the left side.
| Discussion|| |
In this morphometric study of SF, we found morphometric asymmetry and sexual dimorphism in length of various limbs and the angles between them. Knowledge of morphometric variations of SF is helpful for neurosurgeons and radiologists during operative, and investigating procedures., In comparison to studies by Chakrabarti and Vijayalakshmi (6.23 cm) and Rani et al. (5.64 cm), we report a shorter posterior limb of SF (4.14 cm).
In an analysis of language lateralization and cortical symmetry, Greve et al. did an magnetic resonance imaging-based study. They mention that among brain functions, language is the most lateralized and the cortical language areas are the most asymmetrical. In conclusion, they state that gross cerebral morphometric asymmetry is related to laterality of language function.
Chakrabarti and Vijayalakshmi in a cadaveric study reported a sexually dimorphic SF with a lengthier SF in the left side. Contrary to our study, they report a longer anterior ramus on the right side. While we found only as 8% on right-side and 4% on left-side Y branching, they report 21.6% on the right side and 30% on the left side. We found V-type branching as the most common type, and they report U type as most common. In a morphological study, Witelson and Kigar found the vertical ramus to be twice as larger on the right side, while the horizontal ramus was twice as larger on the left side. The anterior ramus did not show any variation in length on both sides. We found the posterior ramus to be longer (10.3%) on the left side. We also found the left anterior ramus to be longer than the right side. Ide et al. conducted a morphometric study of SF in Chile to determine sexual dimorphism and interhemispheric differences. They found the superior ascending ramus larger in males and on the right side. Both ascending and anterior rami were of approximately equal size in females and on the left side. However, in contradiction, we found ascending ramus to be larger than anterior ramus and on the left side in both males and females. In a cadaveric study by, Boni et al. found that the length of SF in left hemisphere more than right hemisphere. This is similar to our finding. Bartley also confirm our findings with similar findings of left lateral sulcus length being more than the left side.
Rani et al. state that interhemispheric asymmetries are associated with hemispheric specialization of speech areas. Embryological lateralization starts in the 29th–30th week of gestation. They give observations of U-, V-, and Y-shaped branching of SF in 40%, 52%, and 8% on the right side and 28%, 48%, and 24% on the left side, respectively. Their finding of maximum number of V shape on the right and left sides contradicts our findings of maximum number of U shape on both sides. Idowu et al. in an autopsy brain study found that speech and language function is one of the most lateralized cerebral functions. Particularly, in consideration to the clinical and functional asymmetry of language expression, the leftward asymmetry of pars triangularis and pars opercularis can exist. During intraoperative dissection, sound knowledge of the gross structure and variations will be of vital importance for the neurosurgeons.
Other primate brains also display sexual dimorphism in SF morphometry. Liu and Phillips did a comparative study of SF in capuchin monkeys. These monkeys with large size of brain, socially complex, and rich vocal repertoire showed sex differences in SF lateralization. Females showed significant leftward lateralization of SF.
Ngando et al. state that knowledge of variations in anatomy of SF will help neurovascular surgeons in training. Many postoperative complications such as formation of ischemic lesions or brain edema are related to anatomical variations of SF. Procedure-related morbidity will decrease significantly with preoperative knowledge of SF variations and adapted surgical approach.
We found the angle between ascending and anterior rami to be more in females and on the left side. This angle lodges the Broca's speech area in the dominant hemisphere. The difference in the physical characteristics of the length and angles may probably influenced by the dominant functioning of the related areas of the cerebrum. These findings may indicate that females have more area for Broca's speech area on the left side. Considering the Broca's speech area is larger in dominant hemisphere, we can say more number of female cadavers in our study have left hemisphere as dominant and are right handed individuals. A larger sample size and regional studies are required to confirm this hypothesis globally. Morphometric asymmetry points toward laterality of the Broca's speech area to the left side. Knowledge about sexual dimorphism and morphometric asymmetry in SF is of prime importance for neurosurgeons during operative procedures.
Limitations of the study
Morphometric evaluation of the SF in people with known hand preference or cerebral dominance shall lead to greater structure-function correlation. Inclusion of the anatomical configuration of the SF along with the morphometry would have resulted in structural evaluation of SF for microsurgical aneurysm clipping through pterional approach. In the present study, occurrence and morphometry of triangular sulcus or incisura capitis were not included. Inclusion of proximal segment, distal segment, and inferior Rolandic point would have increased the applicability of the study outcomes in pterional approach.
| Conclusion|| |
Posterior, anterior, and ascending limbs of SF were longer on the left side. U-shaped branching was the most common shape bilaterally and in both sexes. The angle between ascending and anterior limbs was found more in females and on the left side, thus reflecting laterality and sexual dimorphism.
The PI has received a stipend from the Indian Council of Medical Research under Short Term Studentship 2018 program.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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