Special issue: Research reportIntralobar fibres of the occipital lobe: A post mortem dissection study
Introduction
When it was published, the atlas of Heinrich Sachs (“The hemispheric white matter of the human brain. Part I: The occipital lobe”, 1892) was saluted by his mentor Wernicke with great enthusiasm. It represented the most accurate description of the intralobar fibres of the occipital lobe ever provided in humans, with a particularly detailed representation of the short associative tracts connecting different portions of the lobe (Fig. 1). At the end of the 19th century, the study of white matter anatomy was revolutionised by the introduction of microscopy and histological preparations of cerebral specimens (Schmahmann and Pandya, 2009). Brains collected at autopsy were fixed, initially using alcohol or chromic acid and only later with formaldehyde. Once the fixation process was completed, thin sections were obtained using the microtome (“as thin as the microtome allows” as stated by Sachs). The hereby obtained slices were stained and scrutinised under the microscope, to reveal the complex organisation in layers and fascicles of the white matter. Great neuroanatomists of the time, including Meynert (1833–1892), Flechsig (1847–1929) and Wernicke (1848–1900), applied these novel histological techniques to investigate white matter anatomy (Catani, Forkel, & Thiebaut de Schotten, 2010). Heinrich Sachs, under the tutorage of Wernicke, applied the histological method to the detailed study of the white matter of the occipital lobe. His method consisted of preparing the sections with celloidin, and then treating them with the Pal-haematoxylin and the picro-carmine stains (the former being a specific myelin stain) (Whethered, 1888, Forkel et al., 2014). Surprisingly, little attention has been paid to the work of Sachs after; one reason being that his work was only available in German. The importance of the anatomy and function of the short associative fibres – emphasised in the work of Sachs – has also long been neglected (Catani et al., 2012).
Less than half a century after the publication of Sachs' atlas, a new technique was developed by Joseph Klingler (1935). Working as an anatomical preparator at the University of Basel (Switzerland), Klingler introduced the process of freezing the brains previously fixed in formalin (Agrawal et al., 2011). The freezing process is a crucial step, since the ice that forms between the fibres separates the white matter fascicles, thus facilitating the dissection. The Klingler method greatly improved the techniques of gross dissection of the white matter of the brain, allowing for more accurate anatomical investigations (Ludwig & Klingler, 1956).
In recent years, the advancement of novel in vivo magnetic resonance imaging (MRI) techniques, such as diffusion imaging tractography (Catani and Thiebaut de Schotten, 2008, Jones et al., 1999, Le Bihan et al., 2001) and the resurgence, particularly in the neurosurgical community, of post mortem dissection according to the Klingler method (Türe, Yaşargil, Friedman, & Al-Mefty, 2000) has reignited an interest in the study of white matter anatomy. In the last decade, several fibre dissection studies have been reported, providing original anatomical data (Fernandez-Miranda et al., 2008, Martino, Vergani, et al., 2010, Peltier et al., 2010) and elucidating the cortical termination of some controversial fascicles (Martino, Brogna, et al., 2010, Sarubbo et al., 2011).
In this work, we present original data obtained according to the Klingler dissection of three neuroanatomically healthy right hemispheres and compare these results with the original description of the occipital white matter provided by Sachs in 1892.
Section snippets
Materials and methods
Klingler dissection was performed on three right hemispheres obtained from the autopsy of two female and one male deceased human subjects, who did not suffer from any neurological and/or psychiatric disease. The specimens were collected at the Newcastle Brain Tissue Resource, Newcastle upon Tyne (UK). The Newcastle Brain Tissue Resource has ethical approval to use post mortem human specimens for research, and it complies with the Human Tissue Act. Specimens were fixed in 10% formalin solution
Surface anatomy of the occipital lobe
On the medial surface of the hemisphere, two prominent sulci defining the anatomy of the occipital lobe were identified in all three hemispheres (Fig. 2a). The parieto-occipital sulcus was recognised at the boundary between the parietal and occipital lobe. This sulcus appeared to be uniformly uninterrupted (Ono, Kubik, & Abernathey, 1990) and separated the precuneus (parietal lobe) from the cuneus (occipital lobe). The calcarine fissure, running from the occipital pole towards the splenium of
The anatomy of intralobar occipital fibres
The atlas of Sachs is one of the most accurate descriptions of the occipital fibres in humans, and it still represents a most valuable basis of comparison for those who want to approach this subject.
In the present study we investigated the intralobar white matter fibres of the occipital lobes preparing three hemispheres according to the Klingler's method. We performed coronal sections of the hemispheres at the same levels described in the historical atlas by Sachs, in order to compare our
Conclusions
The human occipital lobe presents a rich and complex network of intralobar fibres, arranged around the ventricular wall. The general principle whereby short association fibres appear to be more superficial, whilst long ranging association fibres are located further away from the cortex and are in contact with the walls of the ventricle, can be confirmed in this study. Overall, good concordance was observed between our Klingler dissection in three right hemisphere specimens and the histological
Conflict of interest
The authors declare no financial or personal conflict of interest related to the present work.
Acknowledgements
The authors would like to thank the Newcastle Brain Tissue Resource, Institute for Ageing and Health, Newcastle University (Newcastle upon Tyne, UK) for providing the specimens used for the dissections. S.J.F. was funded by Guy's and St. Thomas' Trust Charity (PASTXZA).
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