Neural and vascular architecture of the septum pellucidum: an anatomical study and considerations for safe endoscopic septum pellucidotomy

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OBJECTIVE

The septum pellucidum is a bilateral thin membranous structure representing the border between the frontal horns of the lateral ventricles. Its most examined components are the septal veins due to their surgical importance during endoscopic septum pellucidotomy (ESP), which is a well-accepted method for surgical treatment of unilateral hydrocephalus. It is widely accepted that the septum pellucidum contains nerve fibers as well, but interestingly, no anatomical study has been addressed to its neural components before. The aim of the present study was to identify these elements as well as their relations to the septal veins and to define major landmarks within the ventricular system for neurosurgical use.

METHODS

Nine formalin-fixed human cadaveric brains (18 septa pellucida) were involved in this study. A central block containing both septa pellucida was removed and frozen at −30°C for 2 weeks in 7 cases. The fibers of the septum pellucidum and the adjacent areas including the venous elements were dissected under magnification by using homemade wooden spatulas and microsurgical instruments. In 2 cases a histological technique was used to validate the findings of the dissections. The blocks were sliced, embedded in paraffin, cut in 7-µm-thick slices, and then stained as follows: 1) with H & E, 2) with Luxol fast blue combined with cresyl violet, and 3) with Luxol fast blue combined with Sirius red.

RESULTS

The septum pellucidum and the subjacent septum verum form the medial wall of the frontal horn of the lateral ventricle. Both structures contain nerve fibers that were organized in 3 groups: 1) the precommissural fibers of the fornix; 2) the inferior fascicle; and 3) the superior fascicle of the septum pellucidum. The area directly rostral to the postcommissural column of the fornix consisted of macroscopically identifiable gray matter corresponding to the septal nuclei. The histological examinations validated the findings of the authors’ fiber dissections.

CONCLUSIONS

The nerve elements of the septum pellucidum as well as the subjacent septum verum were identified with fiber dissection and verified with histology for the first time. The septal nuclei located just anterior to the fornix and the precommissural fibers of the fornix should be preserved during ESP. Considering the venous anatomy as well as the neural architecture of the septum pellucidum, the fenestration should ideally be placed above the superior edge of the fornix and preferably dorsal to the interventricular foramen.

ABBREVIATIONS DTI = diffusion tensor imaging; ESP = endoscopic septum pellucidotomy; SV = septum verum.

Article Information

Correspondence Laszlo Barany: Semmelweis University, Budapest, Hungary. laszl.bara@gmail.com.

INCLUDE WHEN CITING Published online August 2, 2019; DOI: 10.3171/2019.5.JNS19754.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Diagram demonstrating the division between the septum pellucidum and the septum verum from a lateral point of view. The septum pellucidum is marked with green and the septum verum with yellow. ASV = anterior septal vein; CC = corpus callosum; CN = caudate nucleus; Fx = fornix; M = interventricular foramen; MTF = mammillothalamic fascicle; SMT = stria medullaris of thalamus; SP = septum pellucidum. Copyright Laszlo Barany. Published with permission. Figure is available in color online only.

  • View in gallery

    The septum pellucidum and its adjacent structures on the right side from a lateral point of view before the dissection. The septal veins are partially covered by the ependyma of the frontal horn (black arrowheads). The black dashed line represents the ventral border of the caudate nucleus. Note the macroscopically identifiable gray matter just anterior to the column of the fornix and the glial sheet (Gratiolet’s canal, white arrowhead) around the horizontal fibers of the anterior commissure. AC = anterior commissure; ASV = anterior septal vein; Fx = fornix; PL = choroid plexus; PSV = posterior septal vein; SMT = stria medullaris of thalamus. Copyright Laszlo Barany. Published with permission. Figure is available in color online only.

  • View in gallery

    The location of the septal nuclei on the right side. The precommissural fibers of the fornix (black arrows) terminate within, whereas the inferior fascicle of the septum pellucidum (white arrows) originates from the septal nuclei (black dotted area in the middle). Note the main trunk of the anterior septal vein (white arrowhead) going through the fibers of the fornix before joining to the internal cerebral vein. The black dashed line represents the ventral border of the caudate nucleus. AC = anterior commissure; CC = corpus callosum; Fx = fornix; SMT = stria medullaris of thalamus. Copyright Laszlo Barany. Published with permission. Figure is available in color online only.

  • View in gallery

    The subdivisions of the medial wall of the frontal horn on the left side. The human septum is composed of the dorsally located septum pellucidum and the subjacent septum verum. The border between them (marked with white dashed line) runs 1 mm above the fornix’s body and curves parallel with the postcommissural column of the fornix, and it terminates at the anterior edge of the septal nuclei (black dotted area), roughly 5 mm anterior to the fornix. The black dashed line represents the ventral border of the caudate nucleus. AC = anterior commissure; CC = corpus callosum; Fx = fornix; MB = mammillary body; MTF = mammillothalamic fascicle; SMT = stria medullaris of thalamus; SP = septum pellucidum. Copyright Laszlo Barany. Published with permission. Figure is available in color online only.

  • View in gallery

    Overview of the neural fibers and subependymal veins of the septum on the left side. The major fascicles and veins of the septum are clearly visible after careful removal of the ependymal layer. The septal veins (white arrowheads) were preserved during the dissection for better visualization of the topographic anatomy of the fibers. Black arrowheads mark the superior fascicle and white arrows mark the inferior fascicle of the septum pellucidum. The precommissural fibers of the fornix are indicated with black arrows. The black dashed line represents the ventral border of the caudate nucleus. AC = anterior commissure; CC = corpus callosum; Fx = fornix; M = interventricular foramen; MTF = mammillothalamic fascicle; SMT = stria medullaris of thalamus. Copyright Laszlo Barany. Published with permission. Figure is available in color online only.

  • View in gallery

    Overview of the histological examinations. The planes of the histological examinations are marked on the macroimage (A); the positions of panels B–D are outlined with white squares. B: Cross-section of myelinated fibers corresponding to the bundle of the superior fascicle of the septum pellucidum. C: Oblique section of fibers (black arrowheads) representing the inferior fascicle of the septum pellucidum. D: Longitudinal section of the precommissural fibers of the fornix (black arrowheads) terminating in the septal nuclei. Black arrows mark the cell bodies of the neurons in the septal nuclei. Luxol fast blue combined with Sirius red, original magnification ×400 (B) and ×200 (C and D). IF = inferior fascicle of the septum pellucidum; PcFx = precommissural column of the fornix; SF = superior fascicle of the septum pellucidum. Copyright Laszlo Barany (panel A). Published with permission. Figure is available in color online only.

  • View in gallery

    Schematic illustration of the neural and vascular components of the septum pellucidum. The superior fascicle of the septum pellucidum is marked with violet, the inferior fascicle of the septum pellucidum is marked with azure, whereas the fornix and its precommissural fibers are yellow. The area proposed for the fenestration during endoscopic septostomy is indicated with the green area above the horizontal plane going through the superior edge of the interventricular foramen. The red area under the anterior septal vein (blue) shows the greatest avascular area of the septum. Placing the fenestration here risks injury of the precommissural fibers of the fornix (black arrowheads) and the septal nuclei. AC = anterior commissure; ASV = anterior septal vein; CC = corpus callosum; CN = caudate nucleus; Fx = fornix; IF = inferior fascicle of the septum pellucidum; M = interventricular foramen; MTF = mammillothalamic fascicle; PL = choroid plexus; SF = superior fascicle of the septum pellucidum; SMT = stria medullaris of thalamus. Copyright Peter Kurucz. Published with permission. Figure is available in color online only.

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