Verma, Roshan http://orcid.org/0000-0001-6560-8875
Reddy, Gontu Gopi Satya Sai http://orcid.org/0000-0002-3004-0746
Prakash, D. N. S. http://orcid.org/0000-0002-8371-7642
Sahni, Daisy http://orcid.org/0000-0003-1543-6897
Article History
Received: 11 November 2021
Accepted: 19 April 2022
First Online: 27 April 2022
Declarations
:
: Facial nerve paralysis is a daunting potential complication of parotid surgery. It can significantly impact the quality of life of the patient and also has medico-legal implications for the surgeon. Various studies have reported the incidence of transient facial nerve palsy up to 50% and permanent facial palsy up to 17% after parotidectomy [CitationRef removed]. It is difficult to predict the precise location of facial nerve during parotidectomy during surgery. The surgeons use a system of reference landmarks that help them to predict with safe margin the location of facial nerve. The most frequently and time-tested used landmarks for intra-operative localization of facial nerve are the retro-mandibular vein [CitationRef removed], the tympanomastoid fissure [CitationRef removed], the tragal pointer [CitationRef removed], the posterior belly of the digastric muscle, and styloid process of the temporal bone [CitationRef removed]. These landmarks are difficult to identify during surgery due to their deep location, small size, or variant anatomy in some clinical situations and there is a need to identify additional reference points that can be more useful in difficult situations during parotidectomy [CitationRef removed].Our technique of identifying trunk of the facial nerve using the mastoid tip-tympanomastoid fissure line (TMS-MP) as reference landmarks has been found to be very useful. The average length of the tympanomastoid line was found to be 17.24 mm (12–26 mm) and in clinical dissection was 18.6 mm (15–22 mm). The facial nerve trunk is found to transect this line at a distance of 8–10 mm from the mastoid tip consistently in 12/14 (85%) cadaveric dissections and in three out of five (60%) clinical dissections during parotidectomy. The advantage of this reference line is that it connects two bony reference landmarks which is less likely to be displaced and this distance is found to be relatively consistent in most dissections.We found that in 12/14 cadaver dissections, the facial nerve trunk was found to bifurcate after crossing this TMS-MP line, and in 2 cadaver dissections, we found the facial nerve trunk to bifurcate before crossing this TMS-MP line, whilst in InternalRef removed only in 1/5 cases we found the facial nerve trunk to bifurcate before crossing the TMS-MP line.Difficulties in identifying the facial nerve trunk were encountered in situation where the nerve was found to bifurcate before crossing the TMS-MP line and in such situations other landmarks were also used to identify the facial nerve. It is also important to look for the facial nerve trunk at appropriate depth. The imaginary line is made at the level of the insertion of the post belly of digastric process to the mastoid tip. Plane of dissection is important to identify the facial nerve and we will miss the nerve if we are superficial or deep to this plane.In the clinical setting, we may encounter bleeding from the posterior auricular artery and its branches which lies distance of 10.42 mm (7–13 mm) from the mastoid tip and 7 mm from the facial nerve trunk. This bleeding can be severe and surgeon may injure the facial nerve trunk inadvertently. We understand that the roles of the posterior belly of the digastric muscle and tympanomastoid suture are consistent landmarks to be used for the identification of facial nerve trunk during parotid surgery. However, our technique advocates tympanomastoid suture-mastoid tip (TMS-MP) line can be used as an additional landmark to identify the trunk of the facial nerve during parotidectomy.This technique makes identification of facial nerve trunk easier and also faster, though our experience in InternalRef removed is small and further larger studies with greater sample and different operating settings are needed to further validate our reference landmark.This material has never been published and is not currently under evaluation in any other peer-reviewed publication.
: The authors declare no competing interests.