The extracranial course of the facial nerve and bony anatomicall and marks for localization of the facial nerve trunk during parotidectomie

ABSTRACT

Paralysis of the facial nerve is a common complication during the surgical removal of parotid gland tumors (parotidectomies). This may be due to the close relationship of the tumor and the facial nerve (along its extracranial course). This study aimed to explore the extracranial course of the facial nerve in terms of branching patterns, bony anatomical landmarks and variations. The sample comprised of 40 facial nerve specimens. The parameters identified and recorded were facial nerve trunk division, branching patterns and variations in terms of connections, course and branching. The parameters were classified and compared according to sex and laterality. Bifurcation of the facial nerve trunk occurred in 90% of cases, whilst trifurcation occurred in only 10%. The cases of trifurcation displayed variations. The frequency of each type of branching pattern was Type I = 7.5%, Type II = 12.5%, Type III = 25%, Type IV = 15%, Type V = 27.5% and Type VI =12.5%. The six types were further categorized into three subtypes based on the origin of the buccal branch. The distance fromthe facial nerve trunk to bony anatomical landmarks was measured viz. mastoid process, angle of the mandible and external auditory canal. Only the distance to the angle of the mandible displayed significant differences according to sex (p-value < 0.001) and laterality (p- value = 0.002). All three landmarks displayed good-excellent reliability (ICC values ranged from 0.82 to 0.95) with regard to bony anatomical landmarks for the localization of the facial nerve trunk. The present study proposes the use of the three subtypes in conjunction with the classification system. Anatomical knowledge of the extracranial course of the facial nerve and its relation to bony anatomical landmarks are of im-portance to surgeons during procedures such as parotidectomies

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