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Parameters |
Right (n=28) |
Left (n=28) |
t' |
p' |
||
Mean |
SD |
Mean |
SD |
|||
Fronto-occipital length (cm) |
19.62 |
1.92 |
18.83 |
1.79 |
4.191 |
<0.001* |
Cerebral width (cm) |
12.51 |
1.22 |
13.04 |
1.52 |
-3.583 |
0.001* |
Sylvian fissure length (cm) |
5.64 |
0.99 |
6.43 |
1.26 |
-5.147 |
<0.001* |
ASP-IRP distance (cm) |
3.28 |
0.86 |
3.36 |
0.94 |
-0.508 |
0.616 |
Presence of Triangular sulcus |
16/26 (61.5%) |
14/26 (53.8%) |
c2=0.315; p=0.575 |
|||
Various configuration of AAR / AHR of SF |
Right (n=25) |
Left (n=25) |
|
|||
U-shaped |
10 (40%) |
7 (28%) |
c2=2.57; p=0.277 |
|||
V-shaped |
13 (52%) |
12 (48%) |
||||
Y-shaped |
2 (8%) |
6 (24%) |
p value<0.05* is highly significant
DISCUSSION
The gross anatomy and functional layout of the brain are organized asymmetrically, with hemispheric specializations for key aspects of language and motor function. These asymmetries are first observed around 29-31 weeks gestation. Various developmental programmes structure the two hemispheres well into childhood and beyond, leading to lateralized differences in maturational rates, dendritic arborization, metabolism, and functional activation.5 In humans, inbreeding (Markow and Martin, 1993)6, poor health conditions, and various neurological disorders, such as schizophrenia, attention deficit disorder, developmental delays in childhood and Down syndrome are positively associated with fluctuating asymmetries.7-11 Asymmetric areas have been reported to have less interhemispheric connections.12
The lateral sulcus (also called Sylvian fissure or lateral fissure) is one of the most prominent structures of the human brain. It begins on the inferior aspect of the cerebral hemisphere and runs laterally to reach the superolateral surface. There it divides into three rami i.e. anterior, ascending and posterior. The anterior and ascending rami are short and run into the frontal lobe while the posterior ramus begins near the temporal pole and runs backwards and slightly upwards. Its posterior most part curves sharply upwards. The sulcus divides both the frontal lobe and parietal lobe above from the temporal lobe below. It is present in both hemispheres of the brain but is longer in the left hemisphere in most people. It is one of the earliest-developing sulci of the human brain. It first appears around the fourteenth gestational week.13
Eberstaller (1890) reported that the posterior horizontal ramus of the left lateral fissure was longer than the right in 63% of a large series of adult brains. The difference averaged 0.64 cm.14 This asymmetry was confirmed by Cunningham (1892) who also pointed out that the right lateral fissure (the posterior horizontal portion) courses posteriorly at a slightly greater upward angle than the left with a mean difference of 4 degrees.15 Rubens et al. (1976) noted a characteristic pattern of divergence of posterior regions of the lateral fissures in 25 of 36 adult brains. He found that after pursuing similar courses, the right lateral fissure angulated sharply upward into the inferior parietal area while the left one continued posteriorly.16 Sylvian fissure was significantly longer on the left side as compared to right in our study. In a study done by Boni et al. (2007) on 42 postmortem adult brains, the lateral sulcus in the right hemisphere had a median of65.11mm and in left hemisphere 79.94mm (16.6% higher in left hemisphere).17 The left SF was significantly longer than the right and both were positively correlated in various other studies.18-20 Ono et al. (1990) detected the absence of anterior ascending rami in 86.66% (13/15) of the right hemispheres and in 93.33% of the (14/15) left hemispheres.21 In our study and the study conducted on 62 hemispheres by Idowu et al.(2014),19 the anterior ascending ramus was present in all the hemispheres. The anterior horizontal and anterior ascending rami of the SF had three major configurations. In a study done by Idowu et al. (2014), the U and V-shaped configuration of branching of anterior ascending and anterior horizontal ramus was seen in 70% According to him, the anterior ascending and anterior horizontal rami of the SF was U-shaped in 37.1% (23/62), V-shaped in 32.3% (20/62) and Y-shaped in 30.65% (19/62) hemispheres.19 Chakrabarti and Vijayalakshmi (2015) also found the U-shaped configuration in maximum number of specimens.20 While in the present study, maximum hemispheres 50% (25/50) depicted V-shaped configuration followed by U-shaped 34% (17/50) and Y-shaped 16% (8/50). In six hemispheres, the shape could not be appreciated well. Ayberk et al. (2012) observed Y-shaped configuration in 39.3% (11/28) and 28.6% (8/28) each with V-shaped and U-shaped configuration which is again contradictory to the findings of our study.22 He noted the triangularis sulcus in 49 hemispheres (79%) i.e. 26 right and 23 left side while we observed it in 30 hemispheres (57.69%) i.e. 16 right and 14 left side. Fronto-occipital length of right side was significantly greater on right side (19.62 cm) than left (18.83 cm) in our study. Cerebral width of left side was significantly greater on left side (13.04 cm) as compared to right (12.51 cm) in the present study. While Idowu et al (2014) found the mean value of FO length to be similar on both sides and the mean value of cerebral width to be 6.71 cm and 6.99 cm respectively on right and left side.19 ASP-IRP distance was more on left side but the values was not significant in the present study. This finding is in concordance with the study of Idowu et al. (2014).19
Anatomical asymmetries may help to explain the range of human talents, recovery from acquired disorders of language function, certain childhood learning disabilities, and some dementing illnesses of middle life (Galaburda et al., 1978).23
The surgeon’s knowledge of the structure and a better appreciation of the range of their variation in the human brain, is vital to interpret functional imaging studies and during intra-operative dissection.24,25
CONCLUSION
Significant difference in fronto-occipital length, cerebral width and Sylvian fissure length indicates that the two brain hemispheres differ structurally and it can be speculated that some morphological asymmetries could be related to other functional hemispheric specialization. To correlate this anatomical asymmetry with the functional aspects, further studies are required.
ACKNOWLEDGEMENTS
I express my gratitude to the staff of the Department of Anatomy for assistance in providing infrastructure facilities and necessary help. Authors are indebted to the residents of the Department especially Dr. Aruna Arya who have helped in measuring the various parameters used in the present study.
Authors acknowledge the immense help received from the scholars whose articles are cited and included in references of this manuscript. The authors are also grateful to authors / editors / publishers of all those articles, journals and books from where the literature for this article has been reviewed and discussed.
Source of Funding: Nil
Conflict of interest: All authors have none to declare.
ABBREVIATIONS USED: SF- Sylvian fissure, PO- Pars opercularis, PO- Pars triangularis, FO- Fronto-occipital, ASP- Anterior Sylvian point, PSP- Posterior Sylvian point, IRP- Inferior Rolandic point, SPSS- Statistical Package for Social Sciences, AHR- Anterior horizontal ramus, AAR- Anterior ascending ramus
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