Key Hole Paramedian Supracerebellar Infratentorial Approach to the Posterior Portion of the Third Ventricle: An Anatomical Morphometrical Study and Technical Note with Illustrative Surgical Cases

Introduction: Approaches to the posterior portion of the third ventricle (PTV) represent a surgical challenge. The endoscopic paramedian supracerebellar infratentorial approach (EPSIA) presents the advantage of accessing the PTV with no violation of neural tissue, minimizing cerebellar retraction and avoiding sacrifice of midline bridging veins. To date, morphometrical data providing a systematic quantification of accessibility and operability parameters to the different PTV boundaries when applying an EPSIA are lacking. We performed an anatomical study in human cadaveric specimens and complemented our anatomical findings with illustrative surgical cases.

Methods: Eight EPSIAs toward the PTV were performed in cadaveric specimens. Optimal approach angles (OA), surgical freedom (SF) and operability indexes (Oi) to the PTV boundaries were assessed. Additionally, a 54-year-old woman and 33-year-old man were operated on PTV tumors applying the EPSIA.

Results: Sagittal OA to ventricle's roof and floor was 36 ± 1.4° and 25.5 ± 3.5° respectively, axial OA to the ipsilateral and contralateral ventricle's wall were 9.5 ± 1.3° and 28.5 ± 1.6°. SF was maximal on the contralateral wall (121.2 ± 19.3 mm²), followed by the roof (112.7 ± 18.8 mm²), floor (106.6 ± 19.2 mm²), and ipsilateral wall (94.1 ± 15.7 mm²). SF was significantly lower along the ipsilateral compared with the contralateral wall (p < 0.01) and roof (p < 0.05). Facilitated surgical maneuvers with multiangled exposure (Oi = 3) was possible up to 8.5 ± 1.07 mm anterior to ventricle's entrance, whereas surgical maneuvers were possible but difficult (Oi = 2) up to 15.25 ± 3.7 mm. From this point, visualization of more anterior was possible up to a distance of 27 ± 2.9 mm, but surgical maneuvers were barely feasible (Oi = 1). EPSIA enabled successful resection of both PTV tumors. Postoperative course was uneventful. Patients recovered without new neurological deficits.

Conclusion: EPSIA can be effective for approaching the PTV, enabling surgery along all boundaries, but especially on the roof and contralateral wall. In the not-enlarged ventricle, surgical maneuvers are feasible up to the level of the Monro foramen, becoming more limited anteriorly.

Publication History

Article published online:
15 February 2022