Use of Novel Micro-Endoscope to Examine Fundus of the Internal Auditory Canal in the Middle Cranial Fossa Approach

Objective: The standard MCF approach, while an excellent approach for accessing tumors of the internal auditory canal (IAC), can be challenging with patients who have a significant amount of tumor in the fundus. A novel micro-endoscope (MES) will enhance visualization of the fundus, which should reduce the risk of residual tumor in the fundus and the subsequent recurrence of tumor.

Method: Ten cadaveric specimens (5—left, 5—right) had a standard middle cranial fossa (sMCF) approach drilled out. The fundus was viewed with the following three devices: (1) standard otomicroscope (2) 30-degree endoscope (3) MES. The cadaveric specimens were kept wet throughout the procedure to prevent drying of the IAC contents and to more closely mimic the operative setting. A 2.5-mm-length pick was placed at Bill's bar. Each modality was used to visualize the length of the pick. We recorded whether or not we were able to obtain a partial or complete visualization of the pick. Representative images were collected to demonstrate visualization of the pick.

Results: The MES allowed full visualization of the length of the pick with 9/10 of the specimens. The 30 degree endoscope offered only a partial view of the pick in each specimen. Standard otomicroscopy never demonstrated visualization of the tip of the instrument. The MES was able to be rested upon bill's bar and provide full visualization of the lateral and inferior region of the fundus.

Conclusion: Visualization of the entire fundus is almost impossible with standard microscopy. Standard endoscopes (2.9 mm and 4.0 mm in diameter) enhance our visualization of this area, but they are bulky and difficult to safely maneuver in close proximity to the fundus. Furthermore, the heat from the light source can transmit thermal energy to the exposed facial nerve. The novel MES is small enough to be placed in the fundus to provide full visualization of the fundus. Additionally, this scope lacks a traditional light source and eliminates the risk of thermal energy. Finally, the scope provides a built-in suction which allows for gentle suctioning of blood which typically obstructs visualization of tumor with a standard scope. The MES is a useful addition to the skull base surgeon's armamentarium in that it allows for facile, safe, and wide-angle view of the fundus.

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Artikel online veröffentlicht:
15. Februar 2022