Histological investigation of the interthalamic adhesion and periventricular region: Evidence for midline neural connectivity

The interthalamic adhesion (IA), which may not be present in all humans, is a midline structure that connects the two thalami within the brain's third ventricle. A review of the known literature regarding the IA shows few histological studies and controversy regarding the organization of neurons within this region. This study conducted an anatomical investigation of the human IA in adult South African samples. Samples were obtained from 20 human adult embalmed cadavers: 11 from brains with a visible IA and 9 from brains without this feature. All the samples were harvested using sagittal sections of the area. Three additional samples were sectioned horizontally, yielding 33 tissue blocks. Before observation, these samples were appropriately processed for light microscopy and stained with haematoxylin and eosin, as well as cresyl violet. The results showed that no specific structural arrangements of the neurons were identifiable. The appearance appeared random, except for a distinguishable range in the frequency and dispersion of specific cells upon basic observation. Microglia were the most abundant cell type, and blood vessels were also observed. This study reports a novel inspection of the general histology of the thalamus, specifically of the IA and the periventricular (PVR) region, in midsagittal sections and three horizontal sections. This study confirmed the presence of pyramidal neurons within the IA, forming a bridge between the PVR region of the thalami, thus providing evidence to suggest that the IA could serve as a potential bridge for neural connections crossing over the brain's midline.