Visualization of the Facial Nerve with Ultra-high-Frequency Ultrasound

Abstract

Background: Profound variations in facial nerve branching, combined with the severe impact of facial palsy on the patient's quality of life, make surgery in this region challenging. Recent advancements in ultrasound (US) technology, including the improved visualization of small structures, have led to a sharp increase in its medical indications in various medical disciplines. We aimed to prove the feasibility of using ultra-high-frequency (UHF) US to visualize the facial nerve and to guide surgeons during surgery on and around the facial nerve.

Methods: A cadaveric study was performed on one hemi-face with a UHF US imaging system and state-of-the-art transducers. Firstly, a transcutaneous US was performed, and the facial nerve branches of interest (zygomatic, buccal, and marginal mandibular branches) were marked using US-guided color-injections of filler mixed with methylene blue. Skin and subcutaneous fat were then removed to simulate the intraoperative field. Secondly, an "intraoperative" US examination was performed, and the same branches were marked by US-guided color-injections of filler mixed with indocyanine green. Anterograde facial nerve dissection was performed, and the distance between the nerve branches and the injected filler was measured.

Results: All color-injections (mixed with both methylene blue and indocyanine green) were positioned right next to the nerve branches (<1 mm). The image quality of the US below the skin was observed to be far superior to that of the transcutaneous US.

Conclusion: UHF US can be used to visualize the facial nerve with high precision both transcutaneously and intraoperatively (after elevation of the skin flap).

Fig. 1.

Injection of filler with methylene blue during transcutaneous US.

Fig. 2.

Position of US system during the intraoperative part of the experiment (after diversion of skin flap). Ultrasound is performed over the superficial musculoaponeurotic system.

Fig. 3.

Axial US visualization of trifurcation of the upper division of the facial nerve. Firstly, axial scanning of nerve structures was performed, followed by careful rotation to the longitudinal view, making sure the nerve was kept in the middle of the image (dynamic nature of US).

Fig. 4.

Axial US visualization of the zygomatic and buccal branch of the facial nerve.

Fig. 5.

Close-up of completed dissection, showing the injected filler (indocyanine green/methylene blue) right next to the most important nerve branches. The white star in the top right marks the two small temporal branches crossing the zygomatic arch.