Paraffin embedding of the whole human cerebral hemisphere to assess arterial distribution territories.

Commonly used to decode the human brain's structural complexity, ex vivo dissection focuses on a given structure or region but cannot depict the whole brain organization (for example, its arterial distribution territories). Where dissection reaches its limit, the combination of tissue sectioning and 3D reconstruction may provide a volume for the assessment of structures from any view angle, following them dynamically to understand their spatial relationships. However, to produce sections, standard histological tissue processing protocols for paraffin embedding cannot be applied to a cerebral hemisphere as the latter is extensively larger than the conventional specimens. This paper presents a protocol for paraffin embedding of the whole human cerebral hemisphere and a method to reconstruct 3D volumes from serially sectioned and photographed paraffin blocks containing embedded hemispheres. Seven ex vivo whole human cerebral hemispheres were included, two were serially sectioned. Main cerebral arteries were injected with colored media to label arterial territories. A detailed description of every step, from tissue processing to image acquisition of cut blockfaces and volume reconstruction, is provided. Tissue processing and section cutting were reproducible, and the former provided complete and homogeneous paraffin wax impregnation. 3D visualization of the reconstructed whole human cerebral hemisphere successfully showed the distribution territories of the main cerebral arteries. In addition, we discuss the challenges we faced and overcame while developing the presented method and highlight its originality.

Direct Inside-Out Observation of Superficial White Matter Fasciculi in the Human Brain.

Background: Recent methodological advances in the study of the cerebral white matter have left short association fibers relatively underexplored due to their compact and juxtacortical nature, which represent significant challenges for both post-mortem post-cortex removal dissection and magnetic resonance-based diffusion imaging. Objective: To introduce a novel inside-out post-mortem fiber dissection technique to assess short association fiber anatomy. Methods: Six cerebral specimens were obtained from a body donation program and underwent fixation in formalin. Following two freezing and thawing cycles, a standardized protocol involving peeling fibers from deep structures towards the cortex was developed. Results: The inside-out technique effectively exposed the superficial white matter. The procedure revealed distinguishable intergyral fibers, demonstrating their dissectability and enabling the identification of their orientation. The assessment of layer thickness was possible through direct observation and ex vivo morphological magnetic resonance imaging. Conclusion: The inside-out fiber technique effectively demonstrates intergyral association fibers in the post-mortem human brain. It adds to the neuroscience armamentarium, overcoming methodological obstacles and offering an anatomical substrate essential for neural circuit modeling and the evaluation of neuroimaging congruence. Impact statement The inside-out fiber dissection technique enables a totally new perception of cerebral connectivity as the observer navigates inside the parenchyma and looks toward the cerebral surface with the subcortical white matter and the cortical mantle in place. This approach has proven very effective for exposing intergyral association fibers, which have shown to be much more distinguishable from an inner perspective. It gave rise to unprecedented images of the human superficial white matter and allowed, for the first time, direct observation of this vast mantle of fascicles on entire cerebral hemisphere aspects.

Using ex vivo arterial injection and dissection to assess white matter vascularization.

Advances in the techniques for assessing human cerebral white matter have recently contributed to greater attention to structural connectivity. Yet, little is known about the vascularization of most white matter fasciculi and the fascicular composition of the vascular territories. This paper presents an original method to label the arterial supply of macroscopic white matter fasciculi based on a standardized protocol for post-mortem injection of colored material into main cerebral arteries combined with a novel fiber dissection technique. Twelve whole human cerebral hemispheres obtained post-mortem were included. A detailed description of every step, from obtaining the specimen to image acquisition of its dissection, is provided. Injection and dissection were reproducible and manageable without any sophisticated equipment. They successfully showed the arterial supply of the dissected fasciculi. In addition, we discuss the challenges we faced and overcame during the development of the presented method, highlight its originality. Henceforth, this innovative method serves as a tool to provide a precise anatomical description of the vascularization of the main white matter tracts.

Cerebral white matter vasculature: still uncharted?

White matter vasculature plays a major role in the pathophysiology of permanent neurological deficits following a stroke or progressive cognitive alteration related to small vessel disease. Thus, knowledge of the complex vascularization and functional aspects of the deep white matter territories is paramount to comprehend clinical manifestations of brain ischaemia. This review provides a structured presentation of the existing knowledge of the vascularization of the human cerebral white matter from seminal historical studies to the current literature. First, we revisit the highlights of prenatal development of the endoparenchymal telencephalic vascular system that are crucial for the understanding of vessel organization in the adult. Second, we reveal the tangled history of debates on the existence, clinical significance and physiological role of leptomeningeal anastomoses. Then, we present how conceptions on white matter vascularization transitioned from the mixed ventriculopetal/ventriculofugal theory, in which a low-flow area was interposed in between concurrent arterial flows, to the purely ventriculopetal theory. The latter model explains variable white matter sensitivity to ischaemia by various organizations of ventriculopetal vessel terminals having different origin/length properties and interconnection patterns. Next, arteries supplying primarily the white matter are described according to their length and overall structure. Furthermore, the known distribution territories, to date, are studied in relation to primary anatomical structures of the human cerebral white matter, emphasizing the sparsity of the 'ground truth' data available in the literature. Finally, the implications for both large vessel occlusion and chronic small vessel disease are discussed, as well as the insights from neuroimaging. All things considered, we identify the need for further research on deep white matter vascularization, especially regarding the arterial supply of white matter fibre tracts.

Stereoscopic Images from Computed Tomography Angiograms.

OBJECTIVE: To present an adaptation of the anaglyph photography technique to be used with radiological images from computed tomography angiograms, enabling stereoscopic visualization of a patient's individual abnormal vascular anatomy for teaching, case discussion, or surgical planning purposes. METHODS: Traditional anaglyph procedures with actual objects yield 2 independent photographs, simulating the image perceived by each eye. Production of anaglyphs from angiograms involve 3 basic procedures: volume rendering, image capture, and image fusion. Volume renderings were reconstructed using a free, open-source DICOM (Digital Imaging and Communications in Medicine) reader. Subsequently, the virtual object was positioned to mimic the operator's angle of view, and different perspectives of the reconstructed volume could be obtained through exclusively horizontal rotation. The 2 images were then fused after their color composition was modified so that each eye would perceive only 1 image when using anaglyph glasses. RESULTS: Forty-three angiograms were reviewed for the purpose of this study and a total of 6 examinations were selected for illustration of the technique. Stereoscopic display was possible for all of them and in the 3 types of support tested: computer monitor, tablet, and smartphone screens. CONCLUSIONS: Anaglyph display of computed tomography angiograms is an effective and low-cost alternative for the stereoscopic visualization of a patient's individual intracranial vascular anatomy.