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Deciphering the frontostriatal circuitry through the fiber dissection technique: direct structural evidence on the morphology and axonal connectivity of the fronto-caudate tract

Spyridon Komaitis, Christos Koutsarnakis, Evgenia Lani, Theodosis Kalamatianos, Evangelos Drosos, Georgios P. Skandalakis, Faidon Liakos, Evangelia Liouta, Aristotelis V. Kalyvas, and George Stranjalis

OBJECTIVE

The authors sought to investigate the very existence and map the topography, morphology, and axonal connectivity of a thus far ill-defined subcortical pathway known as the fronto-caudate tract (FCT) since there is a paucity of direct structural evidence regarding this pathway in the relevant literature.

METHODS

Twenty normal adult cadaveric formalin-fixed cerebral hemispheres (10 left and 10 right) were explored through the fiber microdissection technique. Lateral to medial and medial to lateral dissections were carried out in a tandem manner in all hemispheres. Attention was focused on the prefrontal area and central core since previous diffusion tensor imaging studies have recorded the tract to reside in this territory.

RESULTS

In all cases, the authors readily identified the FCT as a fan-shaped pathway lying in the most medial layer of the corona radiata and traveling across the subependymal plane before terminating on the superolateral margin of the head and anterior part of the body of the caudate nucleus. The FCT could be adequately differentiated from adjacent fiber tracts and was consistently recorded to terminate in Brodmann areas 8, 9, 10, and 11 (anterior pre–supplementary motor area and the dorsolateral, frontopolar, and fronto-orbital prefrontal cortices). The authors were also able to divide the tract into a ventral and a dorsal segment according to the respective topography and connectivity observed. Hemispheric asymmetries were not observed, but instead the authors disclosed asymmetry within the FCT, with the ventral segment always being thicker and bulkier than the dorsal one.

CONCLUSIONS

By using the fiber microdissection technique, the authors provide sound structural evidence on the topography, morphology, and connectional anatomy of the FCT as a distinct part of a wider frontostriatal circuitry. The findings are in line with the tract’s putative functional implications in high-order motor and behavioral processes and can potentially inform current surgical practice in the fields of neuro-oncology and functional neurosurgery.

In Journal of Neurosurgery Volume 135: Issue 3 (Sep 2021)

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Deciphering the frontostriatal circuitry through the fiber dissection technique: direct structural evidence on the morphology and axonal connectivity of the fronto-caudate tract

Spyridon Komaitis, Christos Koutsarnakis, Evgenia Lani, Theodosis Kalamatianos, Evangelos Drosos, Georgios P. Skandalakis, Faidon Liakos, Evangelia Liouta, Aristotelis V. Kalyvas, and George Stranjalis

OBJECTIVE

The authors sought to investigate the very existence and map the topography, morphology, and axonal connectivity of a thus far ill-defined subcortical pathway known as the fronto-caudate tract (FCT) since there is a paucity of direct structural evidence regarding this pathway in the relevant literature.

METHODS

Twenty normal adult cadaveric formalin-fixed cerebral hemispheres (10 left and 10 right) were explored through the fiber microdissection technique. Lateral to medial and medial to lateral dissections were carried out in a tandem manner in all hemispheres. Attention was focused on the prefrontal area and central core since previous diffusion tensor imaging studies have recorded the tract to reside in this territory.

RESULTS

In all cases, the authors readily identified the FCT as a fan-shaped pathway lying in the most medial layer of the corona radiata and traveling across the subependymal plane before terminating on the superolateral margin of the head and anterior part of the body of the caudate nucleus. The FCT could be adequately differentiated from adjacent fiber tracts and was consistently recorded to terminate in Brodmann areas 8, 9, 10, and 11 (anterior pre–supplementary motor area and the dorsolateral, frontopolar, and fronto-orbital prefrontal cortices). The authors were also able to divide the tract into a ventral and a dorsal segment according to the respective topography and connectivity observed. Hemispheric asymmetries were not observed, but instead the authors disclosed asymmetry within the FCT, with the ventral segment always being thicker and bulkier than the dorsal one.

CONCLUSIONS

By using the fiber microdissection technique, the authors provide sound structural evidence on the topography, morphology, and connectional anatomy of the FCT as a distinct part of a wider frontostriatal circuitry. The findings are in line with the tract’s putative functional implications in high-order motor and behavioral processes and can potentially inform current surgical practice in the fields of neuro-oncology and functional neurosurgery.

In Journal of Neurosurgery Publish Before Print

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The frontal longitudinal system as revealed through the fiber microdissection technique: structural evidence underpinning the direct connectivity of the prefrontal-premotor circuitry

Spyridon Komaitis, Aristotelis V. Kalyvas, Georgios P. Skandalakis, Evangelos Drosos, Evgenia Lani, Evangelia Liouta, Faidon Liakos, Theodosis Kalamatianos, Maria Piagkou, John A. Emelifeonwu, George Stranjalis, and Christos Koutsarnakis

OBJECTIVE

The purpose of this study was to investigate the morphology, connectivity, and correlative anatomy of the longitudinal group of fibers residing in the frontal area, which resemble the anterior extension of the superior longitudinal fasciculus (SLF) and were previously described as the frontal longitudinal system (FLS).

METHODS

Fifteen normal adult formalin-fixed cerebral hemispheres collected from cadavers were studied using the Klingler microdissection technique. Lateral to medial dissections were performed in a stepwise fashion starting from the frontal area and extending to the temporoparietal regions.

RESULTS

The FLS was consistently identified as a fiber pathway residing just under the superficial U-fibers of the middle frontal gyrus or middle frontal sulcus (when present) and extending as far as the frontal pole. The authors were able to record two different configurations: one consisting of two distinct, parallel, longitudinal fiber chains (13% of cases), and the other consisting of a single stem of fibers (87% of cases). The fiber chains’ cortical terminations in the frontal and prefrontal area were also traced. More specifically, the FLS was always recorded to terminate in Brodmann areas 6, 46, 45, and 10 (premotor cortex, dorsolateral prefrontal cortex, pars triangularis, and frontal pole, respectively), whereas terminations in Brodmann areas 4 (primary motor cortex), 47 (pars orbitalis), and 9 were also encountered in some specimens. In relation to the SLF system, the FLS represented its anterior continuation in the majority of the hemispheres, whereas in a few cases it was recorded as a completely distinct tract. Interestingly, the FLS comprised shorter fibers that were recorded to interconnect exclusively frontal areas, thus exhibiting different fiber architecture when compared to the long fibers forming the SLF.

CONCLUSIONS

The current study provides consistent, focused, and robust evidence on the morphology, architecture, and correlative anatomy of the FLS. This fiber system participates in the axonal connectivity of the prefrontal-premotor cortices and allegedly subserves cognitive-motor functions. Based in the SLF hypersegmentation concept that has been advocated by previous authors, the FLS should be approached as a distinct frontal segment within the superior longitudinal system.

In Journal of Neurosurgery Volume 133: Issue 5 (Nov 2020)

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Dorsal component of the superior longitudinal fasciculus revisited: novel insights from a focused fiber dissection study

Spyridon Komaitis, Georgios P. Skandalakis, Aristotelis V. Kalyvas, Evangelos Drosos, Evgenia Lani, John Emelifeonwu, Faidon Liakos, Maria Piagkou, Theodosis Kalamatianos, George Stranjalis, and Christos Koutsarnakis

OBJECTIVE

The aim of this study was to investigate the anatomical consistency, morphology, axonal connectivity, and correlative topography of the dorsal component of the superior longitudinal fasciculus (SLF-I) since the current literature is limited and ambiguous.

METHODS

Fifteen normal, adult, formalin-fixed cerebral hemispheres were studied through a medial to lateral fiber microdissection technique. In 5 specimens, the authors performed stepwise focused dissections of the lateral cerebral aspect to delineate the correlative anatomy between the SLF-I and the other two SLF subcomponents, namely the SLF-II and SLF-III.

RESULTS

The SLF-I was readily identified as a distinct fiber tract running within the cingulate or paracingulate gyrus and connecting the anterior cingulate cortex, the medial aspect of the superior frontal gyrus, the pre–supplementary motor area (pre-SMA), the SMA proper, the paracentral lobule, and the precuneus. With regard to the morphology of the SLF-I, two discrete segments were consistently recorded: an anterior and a posterior segment. A clear cleavage plane could be developed between the SLF-I and the cingulum, thus proving their structural integrity. Interestingly, no anatomical connection was revealed between the SLF-I and the SLF-II/SLF-III complex.

CONCLUSIONS

Study results provide novel and robust anatomical evidence on the topography, morphology, and subcortical architecture of the SLF-I. This fiber tract was consistently recorded as a distinct anatomical entity of the medial cerebral aspect, participating in the axonal connectivity of high-order paralimbic areas.

In Journal of Neurosurgery Volume 132: Issue 4 (Apr 2020)

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Defining the relationship of the optic radiation to the roof and floor of the ventricular atrium: a focused microanatomical study

Christos Koutsarnakis, Aristotelis V. Kalyvas, Spyridon Komaitis, Faidon Liakos, Georgios P. Skandalakis, Christos Anagnostopoulos, and George Stranjalis

OBJECTIVE

The authors investigated the specific topographic relationship of the optic radiation fibers to the roof and floor of the ventricular atrium because the current literature is ambiguous.

METHODS

Thirty-five normal, adult, formalin-fixed cerebral hemispheres and 30 focused MRI slices at the level of the atrium were included in the study. The correlative anatomy of the optic radiation with regard to the atrial roof and floor was investigated in 15 specimens, each through focused fiber microdissections. The remaining 5 hemispheres were explored with particular emphasis on the trajectory of the collateral sulcus in relation to the floor of the atrium. In addition, the trajectory of the collateral sulcus was evaluated in 30 MRI scans.

RESULTS

The atrial roof was observed to be devoid of optic radiations in all studied hemispheres, whereas the atrial floor was seen to harbor optic fibers on its lateral part. Moreover, the trajectory of the intraparietal sulcus, when followed, was always seen to correspond to the roof of the atrium, thus avoiding the optic pathway, whereas that of the collateral sulcus was found to lead to either the lateral atrial floor or outside the ventricle in 88% of the cases, therefore hitting the visual pathway.

CONCLUSIONS

Operative corridors accessing the ventricular atrium should be carefully tailored through detailed preoperative planning and effective use of intraoperative navigation to increase patient safety and enhance the surgeon’s maneuverability. The authors strongly emphasize the significance of accurate anatomical knowledge.

In Journal of Neurosurgery Volume 130: Issue 5 (May 2019)