Christophe Destrieux

Automatic parcellation of human cortical gyri and sulci using standard anatomical nomenclature

Precise localization of sulco-gyral structures of the human cerebral cortex is important for the interpretation of morpho-functional data, but requires anatomical expertise and is time consuming because of the brains geometric complexity. Software developed to automatically identify sulco-gyral structures has improved substantially as a result of techniques providing topologically correct reconstructions permitting inflated views of the human brain. Here we describe a complete parcellation of the cortical surface using standard internationally accepted nomenclature and criteria. This parcellation is available in the FreeSurfer package. First, a computer-assisted hand parcellation classified each vertex as sulcal or gyral, and these were then subparcellated into 74 labels per hemisphere. Twelve datasets were used to develop rules and algorithms (reported here) that produced labels consistent with anatomical rules as well as automated computational parcellation. The final parcellation was used to build an atlas for automatically labeling the whole cerebral cortex. This atlas was used to label an additional 12 datasets, which were found to have good concordance with manual labels. This paper presents a precisely defined method for automatically labeling the cortical surface in standard terminology.

The persistent left superior vena cava: anatomical study, pathogenesis and clinical considerations

The persistence of a left superior vena cava (LSVC) is an intrinsically cardiac anomaly, which can lead to serious complications during catheterization via the subclavian or internal jugular vein. We found this anomaly during dissection associated with an abnormal origin of the vertebral artery originating from the aortic arch between the left common carotid and subclavian arteries. The LSVC coursed towards the right atrium through a very dilated coronary sinus ostium. No abnormality of the azygos system was found. A thorough anatomic description was then made with external and internal morphology. The embryonic development and variations are described. Radiological and clinical implications are discussed.

Evidence of a middle longitudinal fasciculus in the human brain from fiber dissection

A rostrocaudal pathway connecting the temporal and parietal lobes was described in monkeys using autoradiography and was named the middle longitudinal fasciculus (MdLF). Recently, the use of diffusion tensor tractography has allowed it to be depicted in human volunteers. In the present study, a technique of fiber dissection was used in 18 cadaveric human brains to investigate the presence of this fasciculus and to detail its anatomical relationships. On the basis of our findings, fiber dissection provides evidence for a long horizontal bundle medial to the arcuate fasciculus and extending to the superior temporal gyrus. Its fibers occupy the lateral‐most layer of the upper portion of the stratum sagittale and partially cover the inferior fronto‐occipital fasciculus, which is situated deeper and slightly inferiorly. Whereas MdLF fibers continue on a relatively superficial level to reach the superior temporal gyrus, the inferior fronto‐occipital fasciculus penetrates the deep temporal white matter and crosses the insular lobe. Although diffusion tensor imaging suggests that the MdLF terminates in the angular gyrus, this was not confirmed by the present study. These long association fibers continue onward posteriorly into upper portions of the occipital lobe. Further studies are needed to understand the role of the MdLF in brain function.

Preserved subcortical volumes and cortical thickness in women with sexual abuse-related PTSD

Posttraumatic stress disorder (PTSD) has been frequently associated with volumetric reductions of grey matter structures (e.g. hippocampus and anterior cingulate), but these results remain controversial, especially in female non-combat-related samples. The present study aimed at exploring whole-brain structures in women with sexual abuse-related PTSD on the basis of cortical and subcortical structure comparisons to a matched pair sample that was well-controlled. Seventeen young women who had experienced sexual abuse and who had a diagnosis of chronic PTSD based on the Clinician Administered PTSD Scale for DSM-IV and 17 healthy controls individually matched for age and years of education were consecutively recruited. Both groups underwent structural magnetic resonance imaging and psychiatric assessment of the main disorders according to Axis I of DSM-IV. The resulting scans were analyzed using automated cortical and subcortical volumetric quantifications. Compared with controls, PTSD subjects displayed normal global and regional brain volumes and cortical thicknesses. Our results indicate preserved subcortical volumes and cortical thickness in a sample of female survivors of sexual abuse with PTSD. The authors discuss potential differences between neural mechanisms of sexual abuse-related PTSD and war-related PTSD.

Principle of structural equation modeling for exploring functional interactivity within a putative network of interconnected brain areas

Functional neuroimaging first allowed researchers to describe the functional segregation of regionally activated areas during a variety of experimental tasks. More recently, functional integration studies have described how these functionally specialized areas, interact within a highly distributed neural network. When applied to the field of neurosciences, structural equation modeling (SEM) uses theoretical and/or empirical hypotheses to estimate the effects of an experimental task within a putative network. SEM represents a linear technique for multivariate analysis of neuroimaging data and has been developed to simultaneously examine ratios of multiple causality in an experimental design; the method attempts to explain a covariance structure within an anatomical constrained model. This method, when combined with the concept of effective connectivity, can provide information on the strength and direction of the functional interactions that take place between identified brain regions of a putative network.

Fronto-orbital Sphenoidal Fibrous Dysplasia

We report the clinical, radiological, and histological features of an 8-year-old boy with an unusual presentation of fronto-orbital sphenoidal fibrous dysplasia. The various forms of fibrous dysplasia are outlined and the differential diagnosis discussed. An approach to surgical management is proposed.

Precuneus and Cingulate Cortex Atrophy and Hypometabolism in Patients with Alzheimer’s Disease and Mild Cognitive Impairment: MRI and 18F-FDG PET Quantitative Analysis Using FreeSurfer

Objective. The objective of this study was to compare glucose metabolism and atrophy, in the precuneus and cingulate cortex, in patients with Alzheimers disease (AD) and mild cognitive impairment (MCI), using FreeSurfer. Methods. 47 individuals (17 patients with AD, 17 patients with amnestic MCI, and 13 healthy controls (HC)) were included. MRI and PET images using 18F-FDG (mean injected dose of 185 MBq) were acquired and analyzed using FreeSurfer to define regions of interest in the hippocampus, amygdala, precuneus, and anterior and posterior cingulate cortex. Regional volumes were generated. PET images were registered to the T1-weighted MRI images and regional uptake normalized by cerebellum uptake (SUVr) was measured. Results. Mean posterior cingulate volume was reduced in MCI and AD. SUVr were different between the three groups: mean precuneus SUVr was 1.02 for AD, 1.09 for MCI, and 1.26 for controls (p < 0.05); mean posterior cingulate SUVr was 0.96, 1.06, and 1.22 for AD, MCI, and controls, respectively (p < 0.05). Conclusion. We found graduated hypometabolism in the posterior cingulate cortex and the precuneus in prodromal AD (MCI) and AD, whereas atrophy was not significant. This suggests that the use of 18F-FDG in these two regions could be a neurodegenerative biomarker.

FIBRASCAN: a novel method for 3D white matter tract reconstruction in MR space from cadaveric dissection.

INTRODUCTION Diffusion tractography relies on complex mathematical models that provide anatomical information indirectly, and it needs to be validated. In humans, up to now, tractography has mainly been validated by qualitative comparison with data obtained from dissection. No quantitative comparison was possible because Magnetic Resonance Imaging (MRI) and dissection data are obtained in different reference spaces, and because fiber tracts are progressively destroyed by dissection. Here, we propose a novel method and software (FIBRASCAN) that allow accurate reconstruction of fiber tracts from dissection in MRI reference space. METHOD Five human hemispheres, obtained from four formalin-fixed brains were prepared for Klinglers dissection, placed on a holder with fiducial markers, MR scanned, and then dissected to expose the main association tracts. During dissection, we performed iterative acquisitions of the surface and texture of the specimens using a laser scanner and two digital cameras. Each texture was projected onto the corresponding surface and the resulting set of textured surfaces was coregistered thanks to the fiducial holders. The identified association tracts were then interactively segmented on each textured surface and reconstructed from the pile of surface segments. Finally, the reconstructed tracts were coregistered onto ex vivo MRI space thanks to the fiducials. Each critical step of the process was assessed to measure the precision of the method. RESULTS We reconstructed six fiber tracts (long, anterior and posterior segments of the superior longitudinal fasciculus; Inferior fronto-occipital, Inferior longitudinal and uncinate fasciculi) from cadaveric dissection and ported them into ex vivo MRI reference space. The overall accuracy of the method was of the order of 1mm: surface-to-surface registration=0.138mm (standard deviation (SD)=0.058mm), deformation of the specimen during dissection=0.356mm (SD=0.231mm), and coregistration surface-MRI=0.6mm (SD=0.274mm). The spatial resolution of the method (distance between two consecutive surface acquisitions) was 0.345mm (SD=0.115mm). CONCLUSION This paper presents the robustness of a novel method, FIBRASCAN, for accurate reconstruction of fiber tracts from dissection in the ex vivo MR reference space. This is a major step toward quantitative comparison of MR tractography with dissection results.

How Klingler’s dissection permits exploration of brain structural connectivity? An electron microscopy study of human white matter

The objective of this study is to explore histological and ultrastructural changes induced by Klingler’s method. Five human brains were prepared. First, the effects of freezing–defrosting on white matter were explored with optical microscopy on corpus callosum samples of two brains; one prepared in accordance with the description of Klingler (1956) and the other without freezing–defrosting. Then, the combined effect of formalin fixation and freezing–defrosting was explored with transmission electron microscopy (EM) on samples of cingulum from one brain: samples from one hemisphere were fixed in paraformaldehyde–glutaraldehyde (para/gluta), other samples from the other hemisphere were fixed in formalin; once fixed, half of the samples were frozen–defrosted. Finally, the effect of dissection was explored from three formalin-fixed brains: one hemisphere of each brain was frozen-defrosted; samples of the corpus callosum were dissected before preparation for scanning EM. Optical microscopy showed enlarged extracellular space on frozen samples. Transmission EM showed no significant alteration of white matter ultrastructure after formalin or para/gluta fixation. Freezing–defrosting created extra-axonal lacunas, larger on formalin-fixed than on para/gluta-fixed samples. In all cases, myelin sheaths were preserved, allowing maintenance of axonal integrity. Scanning EM showed the destruction of most of the extra-axonal structures after freezing–defrosting and the preservation of most of the axons after dissection. Our results are the first to highlight the effects of Klingler’s preparation and dissection on white matter ultrastructure. Preservation of myelinated axons is a strong argument to support the reliability of Klingler’s dissection to explore the structure of human white matter.

The inter-optic course of a unique precommunicating anterior cerebral artery with aberrant origin of an ophthalmic artery: an anatomic case report

Background and importanceSome variations of the cerebral arterial circle of Willis, such as an inter-optic course of the anterior cerebral artery are exceedingly rare. Imaging of very rare anatomical features may be of interest.Clinical presentationIn a 67-year-old male individual, the unique precommunicating part of the left anterior cerebral artery was found to course between both optic nerves. There was an agenesis of the right precommunicating cerebral artery. This variation was associated with an aberrant origin of the ophthalmic artery, arising from the anterior cerebral artery. The anatomic features, the possible high prevalence of associated aneurysms of the anterior communicating artery complex as well as implications for surgical planning or endovascular treatments are outlined and embryologic considerations are discussed.ConclusionTo the best of our knowledge, this is a very rare illustrated case of an inter-optic course of a unique precommunicating anterior cerebral artery with aberrant origin of an ophthalmic artery.