Stereotactic anatomy of the third ventricle

Abstract

Purpose: Endoscopic third ventriculostomy (ETV) is a surgical procedure that can lead to complications and requires detailed preoperative planning. This study aimed to provide a more accurate understanding of the anatomy of the third ventricle and the location of important structures to improve the safety and success of ETV.

Methods: We measured the stereotactic coordinates of six points of interest relative to a predefined stereotactic reference point in 23 cadaver brain hemi-sections, 200 normal brain magnetic resonance imaging (MRI) scans, and 24 hydrocephalic brain MRI scans. The measurements were statistically analyzed, and comparisons were made.

Results: We found some statistically significant differences between genders in MRIs from healthy subjects. We also found statistically significant differences between MRIs from healthy subjects and both cadaver brains and MRIs with hydrocephalus, though their magnitude is very small and not clinically relevant. Some stereotactic points were more posteriorly and inferiorly located in cadaver brains, particularly the infundibular recess and the basilar artery. It was found that all stereotactic points studied were more posteriorly located in brains with hydrocephalus.

Conclusion: The study describes periventricular structures in cadaver brains and MRI scans from healthy and hydrocephalic subjects, which can guide neurosurgeons in planning surgical approaches to the third ventricle. Overall, the study contributes to understanding ETV and provides insights for improving its safety and efficacy. The findings also support that practicing on cadaveric brains can still provide valuable information and is valid for study and training of neurosurgeons unfamiliar with the ETV technique.

Keywords: Endoscopic third ventriculostomy; Hydrocephalus; Neuroanatomy; Neuronavigation; Stereotactic coordinates; Third ventricle.

Fig. 1

A External view of the interpeduncular fossa. The Liliequist membrane extends from the optic chiasm ( +) to the anterior pontine surface. Both diencephalic and mesencephalic segments of the Liliequist membrane and the pair of diencephalic-mesencephalic leaves (DML) (white arrow) are present. The DML gave arachnoid sheets to the anteromedial surface of the oculomotor nerve (*). B External view of the third ventricle floor in the interpeduncular fossa and its surrounding structures after Liliequist membrane dissection. C Medial view of the left cerebral hemisphere. The corpus callosum is seen cut in sagittal view and branches of the anterior cerebral artery follow its surface. The midline pineal gland projects posteriorly into the quadrigeminal cistern and is located just rostral to the superior colliculus. The great cerebral vein receives blood from deep structures via the internal cerebral vein. The third ventricle can be seen, including the interthalamic adhesion (*). The basilar artery terminates by giving off the posterior cerebral arteries within the interpeduncular cistern. The lamina terminalis (white arrow) stretches upward to fill the interval between the optic chiasm and the rostrum of the corpus callosum. The rostral portion of the third ventricle contains the supraoptic recess (black arrow) cranial to the optic chiasm. The tuber cinereum ( +) and mammillary body are located on the inferior surface of the hypothalamus. D Medial view of the right cerebral hemisphere. Several anatomic landmarks were used as reference points to better characterize the anatomy of the third ventricle. The anterior commissure-posterior commissure line was drawn (red line) and chosen as Y-axis as it serves as an accurate guide for identifying intracerebral structures. The Z-axis (blue dotted line) was drawn, passing through the posterior and superior portions of the anterior commissure. The intersection of both axes defined the stereotactic reference point (X). Six additional anatomic points (A–F) were used in the characterization of the anatomy of the third ventricle. A)Midline projection of the anterior border of the interventricular foramen; B midline projection of the posterior border of the interventricular foramen; C mammillary bodies anterosuperior portion; D most inferior point of the infundibular recess; E most superior point of the basilar artery; F midline projection of the emergence of the oculomotor nerve. AC anterior commissure; ACA anterior cerebral artery; BA basilar artery; CC corpus callosum; CF Column of the fornix; DS diencephalic segment; GCV great cerebral vein; ICA internal carotid artery; ICV internal cerebral vein; Inf infundibulum; IVF interventricular foramen; MB mammillary body; MS mesencephalic segment; OC optic chiasm; ON oculomotor nerve; PC posterior commissure; PCA posterior cerebral artery; PCoA posterior communicating artery; PG pineal gland (colour figure online)

Fig. 2

Superior view of the floor of the frontal horns and bodies of the lateral ventricles to understand and document the trajectory followed by an endoscope in an approach to the third ventricle. In the lateral walls of both ventricles structures it is seen the head of the caudate nucleus. In each ventricle, the thalamostriate vein (*), caudate veins ( +), choroidal veins (#), and septal veins (white arrow) coalesce and drain through the posterior border of the interventricular foramen (§). The body of the fornix project from the inferior edge of the septum pellucidum. The column of the fornix passes anterior to the interventricular foramen (black arrow). The stria terminalis covers the thalamostriate vein in the caudothalamic groove between the medial edge of the caudate nucleus and the superior surface of the thalamus, marking a line of separation between both nuclei (arrowheads). The choroidal plexus lies on the choroidal fissure. ChP choroidal plexus; CN caudate nucleus (head); F fornix; SP septum pelucidum; Th thalamus (colour figure online)

Fig. 3

A Brain MRI. 3D T1-weighted post-contrast, midsagittal plane from normal subjects. The same anatomic landmarks were used as reference points. The anterior commissure-posterior commissure line was drawn (red line) and chosen as Y-axis. The Z-axis (blue dotted line) was drawn passing through the posterior and superior portions of the anterior commissure. The intersection of both axes defined the stereotactic reference point (X). Six additional anatomic points (A–F) were used in the characterization of the anatomy of the third ventricle. B Brain MRI. 3D T1-weighted post-contrast, midsagital plane from subjects with hydrocephalus. The same anatomical landmarks were used as reference points. A—Midline projection of the anterior border of the interventricular foramen; B—Midline projection of the posterior border of the interventricular foramen; C—Mammillary bodies anterosuperior portion; D—Most inferior point of the infundibular recess; E—Most superior point of the basilar artery; F—Midline projection of the emergence of the oculomotor nerve. Scale bar 10 mm (colour figure online)