Evaluation of surgical approaches to endoscopic auditory brainstem implantation

This study investigates the use of endoscopy for the placement of an auditory brainstem implant by translabyrinthine, retrosigmoid (suboccipital), and middle cranial fossa approaches.

Cadaver dissection and endoscope-assisted placement of the auditory brainstem implant.

Translabyrinthine, retrosigmoid, and middle cranial fossa dissections were performed bilaterally in five cadaveric heads. An auditory brainstem implant was placed within the lateral recess of the fourth ventricle under endoscopic visualization. The implantation was performed with all approaches and documented by digital image capture followed by production of dye-sublimation photographic prints.

The lateral recess was visualized with the endoscope in all three approaches to the brainstem. The 30 degrees endoscope provided the best visualization by translabyrinthine and retrosigmoid dissection and was essential for the middle cranial fossa approach. Refinement of implant position was readily achieved, as even the deepest portion of the recess could be seen with all three approaches.

This study finds that endoscopy provides superior visualization of the lateral recess of the fourth ventricle than the operating microscope with all approaches. The retrosigmoid approach is recommended, as it provides the best view of the implantation site and the easiest angle for placement of the prosthesis. The use of the endoscope may allow for a smaller craniotomy than with conventional microscopic techniques, depending on tumor size. The translabyrinthine approach provides a good view of the lateral recess but had no advantage over other approaches. The middle cranial fossa approach is only possible with angled endoscopes; however, it is technically the most difficult and places the facial nerve at greatest risk.