Stereotactic Localization of the Monro Foramen and the Safest Stereotactic Interforniceal Approach to the Third Ventricle: A Neuroanatomical Study.
OBJECTIVE
To localize the human foramen of Monro stereotactically, to define the anatomical parameters of the safest stereotactic transcallosal transseptal interforniceal approach to the third ventricle, and to show how neurosurgeons could use them in preoperative planning.


METHODS
Our material consisted of 44 formalin-fixated human cerebral hemispheres. We found the location of the anterior (AC) and posterior commissure at the internal hemispheric surface. The posterosuperior border of the AC (point A) was our stereotactic reference point with coordinates (X, Y, Z) = (0, 0, 0). We found the Monro foramen location and measured the stereotactic coordinates of its anterior inferior border (point B). The safest trajectory to the third ventricle has to pass as far as possible from points A and B so as not to traumatize the choroid plexus of the Monro foramina or the AC. The midpoint of the AB distance (point M) is the stereotactic point that provides this safest trajectory. We also measured AB length and point M stereotactic coordinates.


RESULTS
Mean stereotactic coordinates of the (midline projection of the) point B were (X, Y, Z) = (0, -0.6, 2.4). Point B was located averagely 3.2 mm far from point A. Mean stereotactic coordinates of the point M, a necessary component of the trajectory of the safest stereotactic interforniceal approach to the third ventricle, were (X, Y, Z) = (0, -0.3, 1.2). Point M was located 1.6 mm far from point A.


CONCLUSIONS
The present study shows how neurosurgeons can localize and use crucial anatomical landmarks, namely the AC and foramen of Monro, to approach the third ventricle safely via a stereotactic interforniceal technique. This can be achieved during preoperative planning with simple identification of stereotactic points A, B, and M on preoperative median sagittal magnetic resonance images.
Department of Anatomy, University of Athens School of Medicine, Athens, Greece.
Ioannis
I
Mavridis
Department of Anatomy, University of Athens School of Medicine, Athens, Greece.
Sophia
S
Anagnostopoulou
D002552:Cerebral Ventricles / Q000033:anatomy & histology* / Q000601:surgery; D006801:Humans; D019635:Neurosurgical Procedures / Q000379:methods*; D013238:Stereotaxic Techniques; D020542:Third Ventricle / Q000033:anatomy & histology* / Q000601:surgery