Diffusion MRI tractography has emerged as a useful and popular tool for mapping connections between brain regions. In this study, we examined the performance of quantitative anisotropy (QA) in ...facilitating deterministic fiber tracking. Two phantom studies were conducted. The first phantom study examined the susceptibility of fractional anisotropy (FA), generalized factional anisotropy (GFA), and QA to various partial volume effects. The second phantom study examined the spatial resolution of the FA-aided, GFA-aided, and QA-aided tractographies. An in vivo study was conducted to track the arcuate fasciculus, and two neurosurgeons blind to the acquisition and analysis settings were invited to identify false tracks. The performance of QA in assisting fiber tracking was compared with FA, GFA, and anatomical information from T1-weighted images. Our first phantom study showed that QA is less sensitive to the partial volume effects of crossing fibers and free water, suggesting that it is a robust index. The second phantom study showed that the QA-aided tractography has better resolution than the FA-aided and GFA-aided tractography. Our in vivo study further showed that the QA-aided tractography outperforms the FA-aided, GFA-aided, and anatomy-aided tractographies. In the shell scheme (HARDI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 30.7%, 32.6%, and 24.45% of the false tracks, respectively, while the QA-aided tractography has 16.2%. In the grid scheme (DSI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 12.3%, 9.0%, and 10.93% of the false tracks, respectively, while the QA-aided tractography has 4.43%. The QA-aided deterministic fiber tracking may assist fiber tracking studies and facilitate the advancement of human connectomics.
A comprehensive map of the structural connectome in the human brain has been a coveted resource for understanding macroscopic brain networks. Here we report an expert-vetted, population-averaged ...atlas of the structural connectome derived from diffusion MRI data (N = 842). This was achieved by creating a high-resolution template of diffusion patterns averaged across individual subjects and using tractography to generate 550,000 trajectories of representative white matter fascicles annotated by 80 anatomical labels. The trajectories were subsequently clustered and labeled by a team of experienced neuroanatomists in order to conform to prior neuroanatomical knowledge. A multi-level network topology was then described using whole-brain connectograms, with subdivisions of the association pathways showing small-worldness in intra-hemisphere connections, projection pathways showing hub structures at thalamus, putamen, and brainstem, and commissural pathways showing bridges connecting cerebral hemispheres to provide global efficiency. This atlas of the structural connectome provides representative organization of human brain white matter, complementary to traditional histologically-derived and voxel-based white matter atlases, allowing for better modeling and simulation of brain connectivity for future connectome studies.
The structure and function of the arcuate fascicle is still controversial. The goal of this study was to investigate the asymmetry, connectivity, and segmentation patterns of the arcuate fascicle. We ...employed diffusion spectrum imaging reconstructed by generalized q-sampling and we applied both a subject-specific approach (10 subjects) and a template approach (q-space diffeomorphic reconstruction of 30 subjects). We complemented our imaging investigation with fiber microdissection of five post-mortem human brains. Our results confirmed the highly leftward asymmetry of the arcuate fascicle. In the template, the left arcuate had a volume twice as large as the right one, and the left superior temporal gyrus provided five times more volume of fibers than its counterpart. We identified four cortical frontal areas of termination: pars opercularis, pars triangularis, ventral precentral gyrus, and caudal middle frontal gyrus. We found clear asymmetry of the frontal terminations at pars opercularis and ventral precentral gyrus. The analysis of patterns of connectivity revealed the existence of a strong structural segmentation in the left arcuate, but not in the right one. The left arcuate fascicle is formed by an
inner or ventral pathway
, which interconnects pars opercularis with superior and rostral middle temporal gyri; and an
outer or dorsal pathway
, which interconnects ventral precentral and caudal middle frontal gyri with caudal middle and inferior temporal gyri. The fiber microdissection results provided further support to our tractography studies. We propose the existence of
primary and supplementary language pathways
within the dominant arcuate fascicle with potentially distinct functional and lesional features.
The middle longitudinal fascicle (MdLF) was originally described in the monkey brain as a pathway that interconnects the superior temporal and angular gyri. Only recently have diffusion tensor ...imaging studies provided some evidence of its existence in humans, with a connectivity pattern similar to that in monkeys and a potential role in the language system. In this study, we combine high-angular-resolution fiber tractography and fiber microdissection techniques to determine the trajectory, cortical connectivity, and a quantitative analysis of the MdLF. Here, we analyze diffusion spectrum imaging (DSI) studies in 6 subjects (subject-specific approach) and in a template of 90 DSI studies (NTU-90 Atlas). Our tractography and microdissection results show that the human MdLF differs significantly from the monkey. Indeed, the human MdLF interconnects the superior temporal gyrus with the superior parietal lobule and parietooccipital region, and has only minor connections with the angular gyrus. On the basis of the roles of these interconnected cortical regions, we hypothesize that, rather than a language-related tract, the MdLF may contribute to the dorsal "where" pathway of the auditory system.
Smile reconstruction using the branches that supply the zygomaticus major muscle as a motor source is an established procedure in facial reanimation surgery for facial paralysis. However, the anatomy ...of the nerve to the muscle remains unclear. Therefore, we herein examined the topographical anatomy of the nerve to the zygomaticus major muscle to obtain more detailed information on donor nerve anatomy. Preserved cadaver dissection was performed under a microscope on 13 hemifaces of 8 specimens. The branches that innervate the zygomaticus major muscle and their peripheral routes medial to the muscle were traced and examined. A median of four (ranges 2–4) branches innervated the zygomaticus major muscle. The proximal two branches (near the muscle origin) arose from the zygomatic branch, the second of which was the major branch. The distal branches (near the oral commissure) arose from the buccal branch or zygomaticobuccal plexus. The vertical distance from the caudal margin of the zygomatic arch to the major branch intersecting point was 19 ± 4.0 mm, while the horizontal distance parallel to the Frankfort plane was 29 ± 5.2 mm. The proximal two branches innervating the zygomaticus major muscle were detected in the majority of specimens. The anatomical findings obtained herein on the nerve to the zygomaticus major muscle will allow for more reliable donor selection in facial reanimation surgery.
The subcomponents of the human superior longitudinal fasciculus (SLF) are disputed. The objective of this study was to investigate the segments, connectivity and asymmetry of the SLF. We performed ...high angular diffusion spectrum imaging (DSI) analysis on ten healthy adults. We also conducted fiber tracking on a 30-subject DSI template (CMU-30) and 488-subject template from the Human Connectome Project (HCP-488). In addition, five normal brains obtained at autopsy were microdissected. Based on tractography and microdissection results, we show that the human SLF differs significantly from that of monkey. The fibers corresponding to SLF-I found in 6 out of 20 hemispheres proved to be part of the cingulum fiber system in all cases and confirmed on both DSI and HCP-488 template. The most common patterns of connectivity bilaterally were as follows: from angular gyrus to caudal middle frontal gyrus and dorsal precentral gyrus representing SLF-II (or dorsal SLF), and from supramarginal gyrus to ventral precentral gyrus and pars opercularis to form SLF-III (or ventral SLF). Some connectivity features were, however, clearly asymmetric. Thus, we identified a strong asymmetry of the dorsal SLF (SLF-II), where the connectivity between the supramarginal gyrus with the dorsal precentral gyrus and the caudal middle frontal gyrus was only present in the left hemisphere. Contrarily, the ventral SLF (SLF-III) showed fairly constant connectivity with pars triangularis only in the right hemisphere. The results provide a novel neuroanatomy of the SLF that may help to better understand its functional role in the human brain.
Objectives/Hypothesis
The contralateral transmaxillary (CTM) approach is a new surgical approach that improves the surgical trajectory relative to the petrous segment of the internal carotid artery ...(ICA). Here, we present our clinical experience with the CTM approach to the petroclival region of the skull base.
Study Design
Retrospective review.
Methods
A retrospective review of 29 patients who underwent a CTM approach for skull base pathology from 2015 to 2020 was performed. Assessment of gross total resection (GTR) was based on postoperative imaging.
Results
The male:female ratio was 15:14, with an average age of 52 years (range = 19–78 years). Diagnoses included: 12 chondrosarcomas, 11 chordomas, two meningiomas, one schwannoma, one metastasis, one petrous apicitis, and one arachnoid cyst. CTM was performed in addition to a transclival approach and ipsilateral transpterygoid approach in all patients. Reconstruction of surgical defects included a vascularized flap in all but two patients: 24 nasoseptal flaps and three lateral nasal wall flaps. The reconstructive flap was on the same side as the CTM approach in 22 of 28 (79%) patients. There were no ICA injuries. In a subset of patients with chondromatous tumors, GTR of the targeted area was achieved in 16 of 22 (73%) evaluable chondromatous tumors. With a median follow‐up of 13 months, 64% of these patients are without disease or dead of other causes; the remainder are alive with disease.
Conclusions
The CTM approach improves the degree of resection of skull base tumors involving the petroclival region using an endoscopic endonasal approach and may minimize risk to the ICA.
Level of Evidence
4 Laryngoscope, 131:294–298, 2021
We sought to investigate the three-dimensional structure of the white matter of the brain by means of the fiber-dissection technique and diffusion-tensor magnetic resonance imaging to assess the ...usefulness of the combination of both techniques, compare their results, and review the potential functional role of fiber tracts.
Fifteen formalin-fixed human hemispheres were dissected according to Klingler's fiber-dissection technique with the aid of 36 to 340 magnification. Three-dimensional anatomic images were created with the use of specific software. Two hundred patients with neurological symptoms and five healthy volunteers were studied with diffusion-tensor magnetic resonance imaging (3 T) and tractographic reconstruction.
The most important association, projection, and commissural fasciculi were identified anatomically and radiologically. Analysis of their localization, configuration, and trajectory was enhanced by the combination of both techniques. Three-dimensional anatomic reconstructions provided a better perception of the spatial relationships among the white matter tracts. Tractographic reconstructions allowed for inspection of the relationships between the tracts as well as between the tracts and the intracerebral lesions. The combination of topographical anatomic studies of human fiber tracts and neuroanatomic research in experimental animals, with data from the clinicoradiological analysis of human white matter lesions and intraoperative subcortical stimulation, aided in establishing the potential functional role of the tracts.
The fiber-dissection and diffusion-tensor magnetic resonance imaging techniques are reciprocally enriched not only in their application to the study of the complex intrinsic architecture of the brain, but also in their practical use for diagnosis and surgical planning.
Ongoing changes in global climate are altering ecological conditions for many species. The consequences of such changes are typically most evident at the edge of a species’ geographical distribution, ...where differences in growth or population dynamics may result in range expansions or contractions. Understanding population responses to different climatic drivers along wide latitudinal and altitudinal gradients is necessary in order to gain a better understanding of plant responses to ongoing increases in global temperature and drought severity. We selected Scots pine (Pinus sylvestris L.) as a model species to explore growth responses to climatic variability (seasonal temperature and precipitation) over the last century through dendrochronological methods. We developed linear models based on age, climate and previous growth to forecast growth trends up to year 2100 using climatic predictions. Populations were located at the treeline across a latitudinal gradient covering the northern, central and southernmost populations and across an altitudinal gradient at the southern edge of the distribution (treeline, medium and lower elevations). Radial growth was maximal at medium altitude and treeline of the southernmost populations. Temperature was the main factor controlling growth variability along the gradients, although the timing and strength of climatic variables affecting growth shifted with latitude and altitude. Predictive models forecast a general increase in Scots pine growth at treeline across the latitudinal distribution, with southern populations increasing growth up to year 2050, when it stabilizes. The highest responsiveness appeared at central latitude, and moderate growth increase is projected at the northern limit. Contrastingly, the model forecasted growth declines at lowland‐southern populations, suggesting an upslope range displacement over the coming decades. Our results give insight into the geographical responses of tree species to climate change and demonstrate the importance of incorporating biogeographical variability into predictive models for an accurate prediction of species dynamics as climate changes.
We used Scots pine populations located at the treeline across a latitudinal gradient covering the northern, central and southernmost populations and across an altitudinal gradient at the rear edge of the distribution to explore growth responses to climatic variability over the last century through dendrochronological methods and developed models based on age, climate and previous growth to forecast growth trends up to year 2100. Temperature was the main factor controlling growth variability, although the timing and strength of climatic variables affecting growth shifted with latitude and altitude. Predictive models forecast a general increase in Scots pine growth at treeline across the latitudinal distribution, with southern populations increasing growth up to year 2050, when it stabilizes. The highest responsiveness appeared at central latitudes, and moderate growth increase is projected at the northern limit. Contrastingly, the model forecasted growth decline at lowland‐southern populations, suggesting an upslope range displacement over the coming decades.
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