Sulcal variability, stereological measurement and asymmetry of Broca's area on MR images

Abstract

Leftward volume asymmetry of the pars opercularis and pars triangularis may exist in the human brain, frequently referred to as Broca's area, given the functional asymmetries observed in this region with regard to language expression. However, post-mortem and magnetic resonance imaging (MRI) studies have failed to consistently identify such a volumetric asymmetry. In the present study, an analysis of the asymmetry of sulco-gyral anatomy and volume of this anterior speech region was performed in combination with an analysis of the morphology and volume asymmetry of the planum temporale, located within the posterior speech region, in 50 healthy subjects using MRI. Variations in sulcal anatomy were documented according to strict classification schemes and volume estimation of the grey matter within the brain structures was performed using the Cavalieri method of stereology. Results indicated great variation in the morphology of and connectivity between the inferior frontal, inferior precentral and diagonal sulci. There were significant inter-hemispheric differences in the presence of (1) the diagonal sulcus within the pars opercularis, and (2) horizontal termination of the posterior Sylvian fissure (relative to upward oblique termination), both with an increased leftward incidence. Double parallel inferior precentral sulci and absent anterior rami of the Sylvian fissure prevented stereological measurements in five subjects. Therefore volumes were obtained from 45 subjects. There was a significant leftward volume asymmetry of the pars opercularis ( P = 0.02), which was significantly related to the asymmetrical presence of the diagonal sulcus ( P < 0.01). Group-wise pars opercularis volume asymmetry did not exist when a diagonal sulcus was present in both or neither hemispheres. There was no significant volume asymmetry of the pars triangularis. There was a significant leftward volume asymmetry of the planum temporale ( P < 0.001), which was significantly associated with the shape of the posterior Sylvian fissure as a unilateral right or left upward oblique termination was always associated with leftward or rightward volume asymmetry respectively ( P < 0.01). There was no relationship between volume asymmetries of the anterior and posterior speech regions. Our findings illustrate the extent of morphological variability of the anterior speech region and demonstrate the difficulties encountered when determining volumetric asymmetries of the inferior frontal gyrus, particularly when sulci are discontinuous, absent or bifid. When the intrasulcal grey matter of this region is exhaustively sampled according to strict anatomical landmarks, the volume of the pars opercularis is leftward asymmetrical. This manuscript illustrates the importance of simultaneous consideration of brain morphology and morphometry in studies of cerebral asymmetry.

Morphometry, Asymmetry and Variations of the Sylvian Fissure and Sulci Bordering and Within the Pars Triangularis and Pars Operculum: An Autopsy Study

“…In some cases the diagonal sulcus does not merge with any of the surrounding sulci and abuts with the SF. Keller et al, described great variation in the morphology of the diagonal sulci and significant inter-hemispheric differences in the presence of the diagonal sulcus within the PO [12]. We noted the diagonal sulcus in 28 hemispheres (45.2%) and a significant higher presence on the left (p=0.000) in concordance with Keller et al…”

“…The presence of the triangularis sulcus was not dependent on the side (p=0.348) or gender (0.622) unlike the diagonal sulcus was side dependent (p= 0.000). variability in the sulcal bordering of the PT and PO, which gives rise to great variability in size, surface area and volume of the PO and PT [12]. Leftward volume asymmetry of the PO and PT may exist in the human brain given the clinical functional asymmetries observed with respect to language expression.…”

“…Leftward volume asymmetry of the PO and PT may exist in the human brain given the clinical functional asymmetries observed with respect to language expression. Contrariwise, post-mortem and magnetic resonance imaging (MRI) studies have failed to consistently identify such a volumetric asymmetry [12]. An emergent question is whether the asymmetry in function is linked to the asymmetry in gross anatomy.…”

Quantification of Volumetric Changes of Brain in Neurodegenerative Diseases Using Magnetic Resonance Imaging and Stereology

“…Nevertheless, the Cavalieri principle in combination with point-counting is ideal for estimating total volumes of various brain and any compartments. Keller et al (2002Keller et al ( , 2007Keller et al ( , 2008 and Acer et al (2008Acer et al ( , 2010) have previously applied this technique to obtain volume estimations of various brain structures such as Broca's area, hippocampus, ventricles, cerebral hemisphere, and cerebellum. In these studies, a set of parallel and equidistant MRIs of the brain is randomly selected, and the ROI is directly estimated on each image by randomly superimposing a grid of points, and subsequently, counting the number of points that fall within the ROI (Keller et al, 2002(Keller et al, , 2008Acer et al, 2008Acer et al, , 2010.…”

Morphological Aspects of the Parietal Lobe in the Lateral Surface of the Brain: An in vivo MRI Study

“…There is no standard method for studying topographical morphology through MRI, and no one sequence is used routinely. Recently, the following methods have been applied: T1-weighted gradient echo T1 GRE [4], T2-weighted gradient echo T2 GRE [5], spoiled GRASS [6], spoiled GRE [7], and T1 IR GRE [8,9]. Given the improvements in MRI equipment, techniques such as the T1-weighted inversion recovery gradient echo T1 IR GRE are no longer economically unfeasible and may be used routinely.…”