Correspondence: A combination of sectional micro‐anatomy and micro‐stereoscopic anatomy is an improved micro‐dissection method

Abstract

It is easy to make errors in estimating the exact size and positioning of neural structures, especially when only using tomographic methods, as a lot of imagination and little precision is required. We found that combining the use of sectional micro‐anatomy and micro‐stereoscopic anatomy is much more accurate. We believe that our study makes a significant contribution to the literature because we believe that using improved methods to examine the neural structure is vital in future research on the micro‐stereoscopic anatomy of the brain.

We recently studied the neural micro‐stereoscopic anatomy of the New Zealand rabbit, a model organism with a relatively simple brain structure compared to that of other vertebrates, for teaching and research purposes. We aimed to improve our understanding of the three‐dimensional structural relationship between the thalamus, cortex, and lateral ventricle (Wu et al., 2021), and discovered several inaccuracies in the tomographic positioning of the lateral ventricle and third ventricle cavity in a paper published in the Journal of Anatomy by Schneider et al., titled: “Brain anatomy of the 4‐day‐old European rabbit” (Schneider et al., 2018). We also observed similar issues in a study by Shek et al. (1986). While communicating with radiologists during our normal clinical work, we also found that radiologists that frequently engage in sectional research are also prone to using sectional data to construct the spatial concept of the three‐dimensional structure, resulting in deviations in the understanding of the three‐dimensional structure. We believe that this occurs because academics who exclusively study sectional anatomy do not have access to three‐dimensional micro‐stereoscopic anatomy data.

Professor Albert L. Rhoton Jr.'s work over the past 20 years has resulted in various discoveries in the field of micro‐stereoscopic anatomy of the human brain and several atlases have been published. Several references to human nervous system already exist (Campero et al., 2014; Ribas et al., 2017; Tanriover et al., 2004; Yagmurlu et al., 2015); however, information on the micro‐stereoscopic anatomy of other vertebrates remains lacking. We believe that our study is of reference importance as we currently live in the era of neuroscience integration. We found that the paper’s atlas explained the relationship between the fimbria and fornix in the midline as follows: One can infer that the fimbria‐fornix (F) continues as the fornix (f), and that the fimbria‐fornix of both hemispheres merge in the midline in figures 4.1 and 5.1 (Schneider et al., 2018).

The micro‐stereoscopic anatomy shown in figures 13 and 14 (Wu et al., 2021) and the tomographic sections in figures 4.2 and 5.1 (Schneider et al., 2018) demonstrate the three‐dimensional structural relationship simply. The fimbria emerge from both sides to the midline, and then continue parallel downward into the ventral side and merge into the rostral end of the thalamus. Observing this complex three‐dimensional structure is significantly improved by a combination of these methods. We also discovered that the slice research method used in the paper could not differentiate the possible gap between the fimbria, fornix, and stria terminalis (the potential gap between the fimbria and the surface of Anterodorsal thalamic nucleus (AD) and Anteroventral thalamic nucleus (AV) of the thalamus is not evident in the stained section of figure 5.1) (Schneider et al., 2018). This potential gap is easily observed when the micro‐stereoscopic anatomy is studied (figures 13 and 14) (Wu et al., 2021). This potential gap is easy to miss if only the tomographic anatomy is examined.

Furthermore, the markings on the lateral ventricle area in the paper’s tomographic images appear to contradict our observations while studying micro‐stereoscopic anatomy. This refers to the position of the lateral ventricle cavity and the scope of the cavity of the third ventricle.

Figure 6.1 (Schneider et al., 2018) depicts the hippocampus’s dorsal and ventral sides as lateral ventricle chambers. The marked scope of the third ventricle appears to extend too far to the ventral surface of the hippocampus. The area between the fimbria and the surface of the thalamus is also labeled as the lateral ventricle cavity in figure 6.2 (Schneider et al., 2018). The space between the hippocampus and its medial thalamus in figure 7.1 (Schneider et al., 2018) is also marked as the lateral ventricle cavity, and the third ventricle cavity appears to extend abnormally between the surfaces of the cingulate cortex on both sides, the medial end of the hippocampus, and the surface of the thalamus

We discovered that the lateral ventricle chamber is surrounded by continuous structures of the cerebri and hippocampus‐fimbria on the dorsal, lateral, and ventral sides of the thalamus during our investigations of micro‐stereoscopic anatomy. The space between the basal surface of the cerebral hemisphere and the surface of the thalamus is a potential space on the brain surface, which is separated from the lateral ventricle cavity by the choroid fissure (figures 9 and 10; Wu et al., 2021). We also believe that the third ventricle cavities marked in the paper’s images are not as vast as they appear, based on our micro‐stereoscopic anatomical figures. The space between the hippocampus, fimbria, and thalamus is not the lateral ventricle cavity, but rather belongs to the extracerebral space between the basal surface of the cerebral hemisphere and the surface of the thalamus.

Figures 11, 14, 15, and 16 (Wu et al., 2021) also demonstrate that the third ventricle does not extend dorsally into the space between the two sides of the cingulate cortex (this space is part of the cerebrum surface in the longitudinal fissure of the interhemispheric brain). The space between the left and right thalamus, which lies behind the caudal end of the Massa intermedia, is part of the third ventricle cavity in the section of the brain behind the caudal end of the corpus callosum. Moreover, the paper did not mark the third ventricle cavity between the thalamus on both sides in figure 7.2 (Schneider et al., 2018).

Sectional microanatomy and micro‐stereoscopic anatomy each have limitations when studied independently. Some delicate structures, such as the potential space around the corpus callosum and hippocampus, are easily damaged during micro‐stereoscopic anatomical research (Wu et al., 2021). Making errors when investigating micro‐stereoscopic anatomy is common. Similarly, investigations based only on tomographic microanatomy have many limitations concerning the understanding the three‐dimensional structure. For example, relying solely on tomographic data to establish the concept of a three‐dimensional structure in the observer’s brain requires a large amount of imagination, which results in inevitable misunderstandings. We believe that future research on the evolution of the thalamus‐cortex network of vertebrates requires an improved understanding of the three‐dimensional structure of the thalamus‐cortex, including three‐dimensional morphology and staining of tissue structure during the integration and development of various disciplines in neuroscience. Data obtained during a microanatomy study will be a more accurate type of multimethod data due to the stereoscopic observation of micro‐stereoscopic anatomy.