Depicting the anatomy of the gyral white matter: ubi sumus? quo vadimus?

A cerebral gyrus is made up of an external layer of folded cortex and an inner core of white matter. The architecture of the core has specific features that make it distinct from the white matter of the deep brain regions. Limited externally by the grey matter that covers the top of the gyrus and the neighbouring sulci, this gyral white matter is made up of a mix of fibre populations with multiple directions and destinations. The presence of densely packed fibres with multiple crossings, the proximity to the cortex and the existence of inter-regional and inter-individual variations make the task of depicting this microanatomy extremely challenging. The topic is, however, of paramount relevance for both fundamental and applied neurosciences. This fibre colocalization is crucial for the functional role of each cerebral region and is key to clinical manifestations in cases of parenchymal damage. As track tracing, imaging and dissection are based on different biological or physical principles, it is natural for their results to sometimes be different, but they are often complementary. As the amount of available information increases, it becomes fragmented due to the multiplicity of methods, target phenomena and studied species. In this scoping review, we present the key concepts and map the primary sources of evidence regarding identifying the fibre pathways that compose the gyral white matter, enabling the discussion of avenues for future research. The general pattern in which these pathways are distributed in the gyral white matter was detailed, and the main variations as a function of brain topography were explained and illustrated with typical examples.

Biometry of the temporomandibular joint using computerized tomography.

PURPOSE: In the present study, we performed biometric characterization of the temporomandibular joints (TMJs) of clinically normal subjects. METHODS: Fifty-one healthy volunteers underwent high-resolution computerized tomography examination of the TMJs in the position of maximal intercuspidation according to a standardized protocol. Frontal and sagittal reconstructions were then performed to obtain measurements and indexes in three planes of space. RESULTS: Correlations are observed with age, gender, amplitude of mouth opening and presence of dental abrasion. The lateral stability index reflects the degree of mobility of the temporo-discal compartment of the joint. The coverage index reflects how much the mandibular condyle is inserted into the articular fossa and may be related to the risk of occurrence and severity of regressive remodeling phenomena. CONCLUSIONS: This study supports the interest in examining morphological aspects of the TMJ and performing intra-articular measurements. The biometric examination of the TMJ has important applications in the domain of TMJ pathology.

Frontal terminations for the inferior fronto-occipital fascicle: anatomical dissection, DTI study and functional considerations on a multi-component bundle.

The anatomy and functional role of the inferior fronto-occipital fascicle (IFOF) remain poorly known. We accurately analyze its course and the anatomical distribution of its frontal terminations. We propose a classification of the IFOF in different subcomponents. Ten hemispheres (5 left, 5 right) were dissected with Klingler's technique. In addition to the IFOF dissection, we performed a 4-T diffusion tensor imaging study on a single healthy subject. We identified two layers of IFOF. The first one is superficial and antero-superiorly directed, terminating in the inferior frontal gyrus. The second is deeper and consists of three portions: posterior, middle and anterior. The posterior component terminates in the middle frontal gyrus (MFG) and dorso-lateral prefrontal cortex. The middle component terminates in the MFG and lateral orbito-frontal cortex. The anterior one is directed to the orbito-frontal cortex and frontal pole. In vivo tractography study confirmed these anatomical findings. We suggest that the distribution of IFOF fibers within the frontal lobe corresponds to a fine functional segmentation. IFOF can be considered as a "multi-function" bundle, with each anatomical subcomponent subserving different brain processing. The superficial layer and the posterior component of the deep layer, which connects the occipital extrastriate, temporo-basal and inferior frontal cortices, might subserve semantic processing. The middle component of the deep layer could play a role in a multimodal sensory-motor integration. Finally, the anterior component of the deep layer might be involved in emotional and behavioral aspects.

Internal derangement of the temporomandibular joint: is there still a place for ultrasound?

OBJECTIVE: The aim of this study was to assess the diagnostic value of articular sounds, standardized clinical examination, and standardized articular ultrasound in the detection of internal derangements of the temporomandibular joint. STUDY DESIGN: Forty patients and 20 asymptomatic volunteers underwent a standardized interview, physical examination, and static and dynamic articular ultrasound. Sensitivity, specificity, and predictive values were calculated using magnetic resonance as the reference test. RESULTS: A total of 120 temporomandibular joints were examined. Based on our findings, the presence of articular sounds and physical signs are often insufficient to detect disk displacement. Imaging by static and dynamic high-resolution ultrasound demonstrates considerably lower sensitivity when compared with magnetic resonance. Some of the technical difficulties resulted from a limited access because of the presence of surrounding bone structures. CONCLUSIONS: The present study does not support the recommendation of ultrasound as a conclusive diagnostic tool for internal derangements of the temporomandibular joint.

Dorsal fronto-parietal connections of the human brain: a fiber dissection study of their composition and anatomical relationships.

The goal of this study was to detail the composition of dorsal fronto-parietal connections in the human brain, focusing on the dorsal component of superior longitudinal fasciculus (SLF), short association fibers, their three-dimensional organization, and relationships with adjacent projection and commissural fibers. Ten human cerebral hemispheres (five left and five right) were obtained from necropsy specimens. The technique for specimen preparation was adapted from that previously described by Ludwig and Klingler for spreading groups of white matter fibers, rendering tracts visible and dissectible. Near the superior border of the hemisphere, we observed an overall organization consisting of a succession of "U" fibers in both sides of a narrow and irregular intermediary layer of white matter. Dissection of the core fibers leads to the corona radiata (intermingled with the callosal radiations) on the lateral aspect and to the callosal radiations at the medial aspect of the hemisphere. Based on our findings, the fiber dissection technique does not provide evidence of the presence of long horizontal association fibers in such location, as suggested by brain imaging techniques. The results of this study lead us to hypothesize that dorsal regions of the frontal and parietal lobes superior to the level of the cingulate sulcus are connected by a succession of short association pathways. Dissectible long association fibers are only encountered in a zone restricted to a lower and deeper portion of the superior parietal lobule. These fibers are clearly integrated in the lower portions of the SLF/arcuate fasciculus complex.