Vertical bundles of the white matter fibers in the pons revisited: preliminary study utilizing the Klingler technique
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The inner structure of the pons contains several layers of transverse and vertical fibers and many nuclei. The vertical bundles are described as fibers of the corticospinal tract, corticonuclear tract, frontopontine tract and parieto-temporopontine tract organized in three layers. The aim of this study was to investigate the structure of the vertical bundles in the ventral pons using the modified Klingler method. Ten brain stem specimens were investigated. Specimens were fixed in 10% formalin, frozen for 24 h to separate nerve fibers by ice crystals, and then unfrozen again in 10% formalin solution. Afterwards, the specimens were dissected using a sharpened spatula. Results point to the existence of three main layers of vertical bundles and a small, constant, and superficial fourth fascicle that is yet to be described in the literature. We propose the name fasciculus longitudinalis superficialis (superficial longitudinal fascicle) for this group of vertical fibers of the pons.
KeywordsPons Corticospinal tract Anatomy Klingler technique Brain stem
The inner structure of the pons is very complex, given that this compact structure contains many crossing neural tracts as well as many nuclei. Frontopontine (FPT), corticospinal (CST), parieto-temporopontine (PTT), corticonuclear (CNT), and cerebellopontine (CrPT) tracts are found in the ventral pons. These tracts are constructed from vertical (FPT, CST, CNT, and PTT) and transverse (CrPT) nerve fibers which cross each other in an inconstant manner (Clara 1959; De Simone et al. 2005; Fernández-Gil et al. 2010; Oh et al. 2003; Standring et al. 2008). The CST is located in the ventrolateral part of the pons. It is arranged in bundles of vertical fibers separated by transverse fibers and pontine nuclei. It is important to note that CST fascicles maintain somatotopic order along their course through the pons (Fernández-Gil et al. 2010; Hong et al. 2010; Hua et al. 2012; Jang 2011; Prats-Galino et al. 2012). Knowledge of the precise anatomical localization of a lesion affecting the pons is crucial to the neurological diagnosis, but imaging a small and compact structure such as the pons or some other part of the brain stem remains problematic due to its complexity (Fernández-Gil et al. 2010; Jang 2011; Skadorwa et al. 2009). Pathologies that may require neurosurgical interventions, such as tumors or cavernous hemangiomas, should be localized in relation to the CST to avoid serious postoperative complications. However, even with modern tractography, this can be a difficult task (Kwon et al. 2011). It is therefore essential to localize the individual neural tracts in the pons.
The aim of this study was to investigate the spatial arrangement of the vertical nerve fibers in the pons.
Materials and methods
Ten human brain stem specimens of both sexes (five women, five men) aged 21–90 years were investigated using the modified Klingler method. The specimens, fixed in 10% formalin, were placed in a freezer at a temperature of – 20 °C for 24 h. The frozen specimens were then placed in 10% formalin solution again. After 24 h, the specimens were dissected in layers using a sharpened spatula and an anatomical needle under a surgical microscope with a magnification of up to 40×. After the removal of each nerve fiber layer, photographic documentation was carried out using a Fujifilm Finepix S1000FD camera.
Studying the pons is a difficult task due to the large number of structures and crossing fibers located in such a small space. Although in vivo imaging techniques are commonly used to examine brain structures, such methods still unable to fully visualize the small, independent nerve fiber bundles that are present in the ventral part of the pons (Kwon et al. 2011; Virta et al. 1999). Recently, the importance of white matter dissection using the Klingler method was stressed, as it provides a means to validate the results of diagnostic imaging (Liakos and Koutsarnakis 2016). Indeed, although Zemmoura (2016) claimed that it is more important for a radiologist to carry out diffusion tractography with different tractography tools while appreciating their limitations than to perform dissection, dissection remains an important source of new anatomical information and discoveries. For example, an electron microscopy study of human white matter performed by the same author (Zemmoura 2016) showed that myelinated axons are preserved during Klingler’s dissection, which provides strong support for the idea of validating tractography using this method. This may be supported by neuronavigation (Skadorwa et al. 2009). In this approach, dissection is validated by navigation or navigation is validated by dissection.
Compliance with ethical standards
Conflict of interest
The authors declare they have no conflict of interest.
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