# Anatomical insights into the peri-trigeminal zone via transorbital, transclival, and retrosigmoid routes: a comparative cadaveric study with surgical implications

## TL;DR

This study compares three surgical approaches to access brainstem lesions, analyzing their anatomical advantages and limitations for safer and more effective procedures.

## Contribution

The study provides a comparative cadaveric analysis of three endoscopic approaches to the peritrigeminal zone, highlighting their anatomical constraints and surgical implications.

## Key findings

- All three approaches provided access to the PTZ but had structural limitations affecting maneuverability.
- The RS and ETTA approaches offered near-tangential visualization, while ETOA provided a more perpendicular view.
- Lesion orientation within the pons is a key factor in selecting the optimal surgical approach.

## Abstract

Surgical access to brainstem (BS) lesions requires small neurotomies in between a dense and complex neural fiber network. Access is gained on the BS surface closest to the lesion to minimize the intraparenchymal trajectory and reduce the risk of neurological injury. The concept of safe-entry zones guides the selection of the most favorable entry point to reduce these risks. Several endoscopic approaches have been validated as safe and effective for accessing the peritrigeminal zone (PTZ); however, each one is limited by anatomical constraints due to adjacent osteo-vascular structures, which restrict the surgical corridor. To evaluate the anatomical advantages and limitations of accessing the PTZ via the endonasal transclival approach (ETTA), retrosigmoid approach (RS), and endoscopic transorbital approach (ETOA).

The ETTA, RS, and ETOA approaches were performed on five human cadaveric specimens (25 approaches). Before dissection, all specimens underwent high-field magnetic resonance imaging, including diffusion tensor imaging (DTI) sequences for tractography reconstruction. An anatomical assessment was then conducted to verify accessibility to the PTZ. The potential surgical trajectory, approach length, and surgical view’s angle were measured and compared across the three approaches.

All approaches allowed access to the PTZ; however, each one exhibited structural limitations affecting surgical maneuverability. Comparative anatomical and radiological analysis highlighted procedural insights to guide the selection of the most appropriate surgical corridor based on lesion morphology. The RS approach, the shortest one, and the ETTA provided a near-tangential visualization of the PTZ, whereas the ETOA offered a more perpendicular surgical view.

A thorough understanding of the anatomical and technical nuances of the three approaches to the PTZ described in this study can support the selection of the most appropriate surgical route for pontine lesions. Comparative data suggest that the orientation of the lesion’s major axis within the pons is a key criterion in determining the optimal surgical approach.