Microanatomy of the Temporal Division of the Facial Nerve in the Periorbital Region Applied to Minimally Invasive Keyhole Approaches

Abstract

Background

Minimally invasive keyhole approaches to the anterior skull base and circle of Willis require small incisions near distal branches of the temporal division (TD) of the facial nerve. Few studies have focused on planning the incision to avoid the TD branches and maximize exposure in these approaches. This study aimed to define a safe zone away from the TD branches for skin incision during minimally invasive keyhole approaches using reliable and practical skin landmarks.

Methods

In 5 cadaveric heads (10 sides), a Cartesian system was established with the orbitomeatal line connecting the lateral canthus and the external acoustic meatus (x-axis). A perpendicular line was drawn to the x-axis at the lateral canthus (y-axis). TD branches were dissected proximally to distally until the nerve-muscle junction of the orbicularis oculi and fronto-occipitalis muscles. Nerve-muscle junction points were registered in the Cartesian system. Probabilistic heat maps were generated to define a periorbital safe zone.

Results

A median of 3 branches each innervated the orbicularis oculi and fronto-occipitalis. A semicircular area centered on the lateral canthus with a radius of 10 mm was found to have low (<10%) chance of containing a TD branch. This safe zone could be extended posteriorly to 15 mm inferior to the orbitomeatal line.

Conclusions

Identifying a safe zone for preserving TD branches is crucial for surgical incisions planned in the superolateral region of the orbit. This study provides a clinically applicable and reproducible landmark for planning incisions commonly used during minimally invasive keyhole approaches.