Endoscopic Lateral Transorbital Approach to Trigeminal, Facial, and Vestibulocochlear Nerves in Comparison to Retrosigmoid Approach with Possible Clinical Applications

Background: Retrosigmoid approach has been widely accepted for the cerebellopontine angle (CPA). Some difficulties can be encountered while performing the approach. Visualization of the trigeminal nerve may be obscured by draining veins such as petrosal veins or by overhanging lip of cerebello-mesencephalic fissure. In microvascular decompression, the offending vessel may be located anteriorly in the axilla of the nerve. In CPA tumors, the relation of the nerves to the tumors plays an important role during surgery. Visualization of the intracanalicular part of the tumor is also challenging in retrosigmoid approach. Some tumors may have a petroclival origin and may displace the trigeminal nerve posteriorly, blocking the view from a retrosigmoid angle.

Objective: To discuss and describe the possible advantages and limitations of the LTO approach over the retrosigmoid approach.

Methods: Five colored latex injected cadaveric heads (10 sides) were dissected with the aid of 0- and 30-degree rod-lens endoscope. On the right side, the retrosigmoid approach was performed first and then the LTO. The opposite order was performed on the left. All the LTO approaches were conducted through lateral orbital rim (LOR) removal and an access to the posterior fossa was gained as previously described. The retrosigmoid approach was performed through a C-shaped incision, 2 cm behind the mastoid tip, followed by a 4 × 4 cm craniotomy exposing both the sigmoid and transverse sinus borders and an opening of the dura in C-shaped fashion. Measurements regarding surgical freedom and angle of attack and distances to the porus trigeminalis, root entry zone, and porus acusticus were measured with the aid of neuronavigation image guidance.

Results: The LTO approach showed an anterior view of the trigeminal nerve, porus trigeminalis and root entry zone. Full exposure of the IAC was also gained through the LTO approach in contrary to the limited exposure by the retrosigmoid approach. Retrosigmoid approach gave better view for structures below the inferior petrosal sinus. Shorter distances to the porus trigeminalis, root entry zone of the trigeminal nerve, and porus acusticus were obtained with the retrosigmoid approach.

Conclusion: Different view of trigeminal, facial, and vestibulocochlear nerves can be obtained by the LTO approach versus the retrosigmoid approach. LTO approach to these nerves may work as an alternative or complementary approach to the retrosigmoid in selective cases, yet clinical experience is needed to fully address the advantages and limitations of the relatively new LTO approach.

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No conflict of interest has been declared by the author(s).