[Histomorphologic findings in the facial nerve after water-jet dissection of the parotid gland in dogs]

Abstract

Background: Initial results on the application of the water-jet in a parotidectomy setting in an animal study demonstrate that there are morphologic changes which do, and some which do not, affect the clinial function of the facial nerve due to the different jet sizes and operating pressures used. In a further study the histomorphometric data of the facial nerve dissected by the water-jet should be evaluated and correlated to the different sizes of jet and operating pressures.

Material and methods: In total, 102 nerves (in 14 beagles) which had been dissected by water-jets of different sizes and operating pressures were evaluated. After an observation period of 21 days, including documentation of the clinical function of the facial nerve, the nerves were dissected. The number of nerve fibers and the diameter of the different nerve fibers were then evaluated.

Results: All nerve fibers dissected with jet sizes of 120 and 150 μm showed an identical cumulative frequency of fiber diameters. All nerve fibers dissected with a water-jet of 200 μm showed morphologic and clinical abnormalities and--in terms of nerve fiber diameters--clear differences to the nerve fibers dissected with 120- or 150-μm jets. Altogether, there is a decrease in fiber diameter along the nerve course.

Conclusion: Our data show a shift of larger diameters of the nerve trunk to smaller diameters in the terminal nerve fibers. This phenomenon has not been described in the literature to date and is probably not due to the water-jet. Additionally, our data show that 22% of the original nerve fiber damaged by the water-jet is sufficient to preserve the nerve's clinical function.