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Challenges Associated With Aberrant Facial Nerve Anatomy in Parotidectomy: A Case Report

Archives of Otorhinolaryngology-Head & Neck Surgery. 2023;7(1):5
DOI: 10.24983/scitemed.aohns.2023.00175
Article Type: Case Report

Abstract

Lesions within the parotid gland can significantly displace the facial nerve, leading to substantial anatomical deviations that undermine the reliability of traditional intraoperative landmarks. These deviations necessitate increased vigilance to prevent iatrogenic injury to the facial nerve during surgery. We describe a challenging case involving a 75-year-old Chinese woman with a parotid lesion that caused an undetected preoperative displacement of the facial nerve. This unexpected deviation from the nerve's typical pathway required intraoperative adaptability. Employing a retrograde dissection technique, as opposed to the conventional anterograde approach, was crucial to preserve the integrity of the facial nerve. Despite the availability of advanced imaging techniques, anatomical anomalies can still significantly complicate surgical procedures. This highlights the need for tailor-made surgical strategies to ensure patient safety and successful outcomes.

Keywords

  • Facial nerve displacement; facial nerve injuries; parotid neoplasms; pleomorphic adenoma

Introduction

Preserving the facial nerve during parotidectomy is of paramount importance. However, the size, position, and involvement of the primary parotid lesion can complicate this endeavor. It is well-documented that both superficial and deep lobe parotid lesions can alter the facial nerve's course [1–3], making standard anatomical landmarks unreliable for identifying the nerve. These deviations from typical facial nerve anatomy add to the surgery's complexity and may lead to an increased risk of postoperative facial paresis.

In this paper, we describe a case that highlights the challenges of aberrant facial nerve anatomy due to a parotid lesion. We also discuss the benefits of employing a retrograde dissection technique rather than the conventional anterograde approach. This method allowed us to preserve the integrity of the facial nerve while effectively managing the parotid lesion.

Case Presentation

A 75-year-old Chinese female presented to our Ear, Nose, and Throat (ENT) clinic with a right neck mass that had persisted for three weeks. The initial computed tomography (CT) scan of the neck displayed a 2.7 × 3.1 × 2.9 cm mass in the superficial right parotid region. A fine needle aspiration (FNA) biopsy suggested a pleomorphic adenoma. The patient defaulted on the follow-up and returned three years later, reporting an increase in the size of her neck mass. Upon physical examination, a 6 cm firm mass was palpable over the right angle of the jaw. No cervical lymphadenopathy was detected, and facial nerve function was intact. Nasoendoscopy findings were within normal limits. A repeat CT scan demonstrated marked growth of the mass, now centered in the superficial parotid gland, with patchy enhancement (Figure 1A), raising suspicions of a low-grade parotid malignancy. There was no radiological evidence of cervical lymph node involvement. The patient was scheduled for surgery to obtain a definitive histological diagnosis.

 

Figure 1. (A) An axial section of the preoperative CT scan illustrates the proximity of the lesion to the retromandibular vein, indicated by the red arrow. (B) Depiction of the main trunk, highlighted by the white arrow, curving posteriorly towards the tragus. (C) The white arrow shows the branches of the facial nerve extending anteriorly across the tumor's surface. (D) The facial nerve and its branches following the excision of the tumor.

 

A superficial parotidectomy was performed with dual-channel facial nerve monitoring (Medtronic NIM-Response 3.0) in accordance with our institution’s standard practice. Intraoperatively, we encountered a large 6 cm tumor located in the anterior portion of the right superficial parotid lobe, extending towards the deep lobe. Initial anterograde dissection attempts, employing standard surgical landmarks (the tragal pointer, the posterior belly of the digastric, and the tympanomastoid suture), were unsuccessful in identifying the pes anserinus, indicating anomalous facial nerve anatomy. Consequently, a decision was made early on to shift to retrograde dissection to circumvent iatrogenic injury to the main nerve trunk.

The pes anserinus was eventually located using the retrograde approach. Following this, the main nerve trunk was discovered to loop posteriorly towards the tragus (Figure 1B), then run anteriorly across the tumor surface, bifurcating into superior and inferior divisions (Figure 1C). All facial nerve branches were meticulously identified and conserved after en bloc tumor excision (Figure 1D).

Given the preoperative FNA diagnosis of pleomorphic adenoma and the imaging features suggestive of a possible low-grade parotid malignancy without nodal involvement, no intraoperative frozen section was performed. The surgical strategy was limited to the parotidectomy alone. At the conclusion of the operation, all branches of the right facial nerve were responsive to stimulation at 0.8 mA.

The final histological analysis confirmed the presence of a pleomorphic adenoma. In the immediate postoperative phase, the patient exhibited right-sided forehead, eye, and mouth movement weakness, graded as House-Brackmann score 4. By the 6-month postoperative follow-up, her condition had improved to a House-Brackmann score of 2.

Discussion

The identification of the facial nerve is crucial in parotid surgery, requiring surgeons to be vigilant of atypical nerve positions, especially when neoplasms may cause displacement. In a certain case series, the incidence of facial nerve displacement associated with superficial lobe tumors was noted to be as high as 38.3% [2]. Diverse displacement patterns have been documented. For instance, pediatric patients with deep lobe parotid tumors have been reported to experience posterolateral nerve displacement and elongation of the main facial trunk [1], whereas vertical displacement has been observed in a case involving locally advanced mucoepidermoid carcinoma [4]. In the case of our patient, the parotid lesion caused such significant elongation and posterior displacement of the main trunk that the nerve formed a 180-degree loop anteriorly as it proceeded to the pes anserinus and the distal branches.

Displacement of the facial nerve's main trunk can render standard anatomical landmarks unreliable, necessitating an adapted surgical approach to prevent iatrogenic injury. In the case discussed, the aberrant anatomy of the main trunk prevented anterograde dissection using conventional landmarks, leading to a strategic shift to the retrograde approach. The critical nature of systematic evaluation of these landmarks, along with prompt decision-making and a resolute commitment to preserving the facial nerve, is paramount in cases featuring atypical anatomy. Insistence on dissection in the absence of recognizable landmarks may compromise the chances of atraumatic preservation of the facial nerve. While the anterograde approach is the routine choice for many surgeons in facial nerve dissection [5], the presence of anomalous anatomy or acquired aberrations, such as in revision parotidectomy cases, requires surgeons to be adept with the retrograde method or a combination of techniques to safely locate the facial nerve. In benign parotid surgery, both approaches are associated with comparable postoperative incidences of transient or permanent facial nerve injury [6].

Preoperative imaging using CT or magnetic resonance imaging (MRI) is instrumental for assessing tumor size and characteristics, as well as for predicting the tumor's location within the parotid gland. Additionally, preoperative imaging can assist in estimating the intraparotid facial nerve's position by evaluating landmarks such as the retromandibular vein. However, anatomical variations in these landmarks may lead to inaccuracies in identifying the facial nerve [7]. Consequently, it is not surprising that radiological predictions of facial nerve positioning have been reported to be accurate in only 69% of cases [8]. Considering this, surgeons might resort to multiple imaging modalities preoperatively to refine surgical planning, carefully assessing the facial nerve's trajectory, where discernible, and the degree of deep lobe involvement in the parotid lesion.

High-resolution MRI protocols that incorporate steady-state sequences and diffusion-weighted imaging have also been employed for direct visualization of the intraparotid facial nerve. A recent systematic review and meta-analysis by Lee et al. has reported facial nerve detection rates as high as 99.8% with the use of these advanced imaging techniques [9]. While such MRI protocols have yet to be universally standardized, they could be considered in situations where aberrant facial nerve anatomy is anticipated. This includes scenarios involving large tumors that extend across both superficial and deep lobes of the parotid or tumors situated near the stylomastoid foramen, potentially leading to altered facial nerve pathways.

The literature extensively details variations in the facial nerve's terminal branches [10,11], yet reports of the main trunk's anatomical deviations are less common. This case report enhances our understanding of the potential for unusual positioning of the main trunk and the possible surgical complications that could follow. Both preoperative imaging and intraoperative nerve monitoring are vital in facilitating the detection and protection of the facial nerve in surgical settings. It is crucial for surgeons to be aware of and prepared for non-standard facial nerve anatomies, employing a range of surgical techniques to secure parotid surgery's safety.

Conclusion

This case report elucidates uncommon anatomical deviations of the main trunk of the facial nerve, which may pose significant surgical complications. It emphasizes the critical role of preoperative diagnostic imaging and vigilant intraoperative neuro-monitoring for the accurate detection and conservation of the facial nerve's integrity. The report advocates for surgeons to maintain a high degree of awareness and preparedness for non-standard anatomical structures when undertaking parotidectomy procedures.

References

  1. Maddalozzo J, Johnston DR, Isaac A, Bhushan B, Rastatter JC. Displacement of the facial nerve by deep parotid lobe lesions in the pediatric population. Laryngoscope Investig Otolaryngol 2019;4(5):550–553. [View Article]
  2. Kashyap SK, Tausif M. Incidence of displacement of facial nerve trunk from normal anatomical position in cases of benign tumour in superficial lobe of parotid gland: A surgical finding and its significance. Indian J Otolaryngol Head Neck Surg 2022;74(Suppl 3):6367–6373. [View Article]
  3. Sardar S, Dutta M, Dutta S, Das S, Sinha R. Do benign mass lesions in the superficial lobe of parotid gland influence landmark-based search for facial nerve trunk at surgery? Medeni Med J 2021;36(1):36–43. [View Article]
  4. Harsha MP, Padha K. Identification of facial nerve displaced vertically in locally invasive mucoepidermoid carcinoma of parotid gland: A rare case discussion. J Oral Biol Craniofac Res 2022;12(5):522–524. [View Article]
  5. O'Regan B, Bharadwaj G, Elders A. Techniques for dissection of the facial nerve in benign parotid surgery: A cross specialty survey of oral and maxillofacial and ear nose and throat surgeons in the uk. Br J Oral Maxillofac Surg 2008;46(7):564–566. [View Article]
  6. Mashrah MA, Al-Dhohrah TA, Al-Zubeiry FA, et al. Antegrade versus retrograde facial nerve dissection in benign parotid surgery: Is there a difference in postoperative outcomes? A meta-analysis. PLoS One 2018;13(10):e0206028. [View Article]
  7. Toure G, Vacher C. Relations of the facial nerve with the retromandibular vein: Anatomic study of 132 parotid glands. Surg Radiol Anat 2010;32(10):957–961. [View Article]
  8. Ragbir M, Dunaway DJ, Chippindale AJ, Latimer J, Mohammed F, McLean NR. Prediction of the position of the intraparotid portion of the facial nerve on MRI and CT. Br J Plast Surg 2002;55(5):376–379. [View Article]
  9. Lee MK, Choi Y, Jang J, et al. Identification of the intraparotid facial nerve on MRI: A systematic review and meta-analysis. Eur Radiol 2021;31(2):629–639. [View Article]
  10. Kopuz C, Turgut S, Yavuz S, Ilgi S. Distribution of facial nerve in parotid gland: Analysis of 50 cases. Okajimas Folia Anat Jpn 1994;70(6):295–299. [View Article]
  11. Poutoglidis A, Paraskevas GK, Lazaridis N, et al. Extratemporal facial nerve branching patterns: Systematic review of 1497 cases. J Laryngol Otol 2022;136(12):1170–1176. [View Article]

Editorial Information

Publication History

Received date: August 29, 2023
Accepted date: October 17, 2023
Published date: November 17, 2023

Disclosure

The manuscript has not been presented or discussed at any scientific meetings, conferences, or seminars related to the topic of the research.

Ethics Approval and Consent to Participate

The study adheres to the ethical principles outlined in the 1964 Helsinki Declaration and its subsequent revisions, or other equivalent ethical standards that may be applicable. These ethical standards govern the use of human subjects in research and ensure that the study is conducted in an ethical and responsible manner. The researchers have taken extensive care to ensure that the study complies with all ethical standards and guidelines to protect the well-being and privacy of the participants.

Funding

The author(s) of this research wish to declare that the study was conducted without the support of any specific grant from any funding agency in the public, commercial, or not-for-profit sectors. The author(s) conducted the study solely with their own resources, without any external financial assistance. The lack of financial support from external sources does not in any way impact the integrity or quality of the research presented in this article. The author(s) have ensured that the study was conducted according to the highest ethical and scientific standards.

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Department of Otorhinolaryngology-Head and Neck Surgery, Changi General Hospital, Singapore, Singapore
Department of Otorhinolaryngology-Head and Neck Surgery, Changi General Hospital, Singapore, Singapore
Department of Otorhinolaryngology-Head and Neck Surgery, Changi General Hospital, Singapore, Singapore
Department of Otorhinolaryngology-Head and Neck Surgery, Changi General Hospital, Singapore, Singapore
Department of Otorhinolaryngology-Head and Neck Surgery, Changi General Hospital, Singapore, Singapore
Email: ian.loh.c.y@singhealth.com.sg
Address: 2 Simei Street 3, Singapore 529889, Singapore
Figure 1.JPG
Figure 1. (A) An axial section of the preoperative CT scan illustrates the proximity of the lesion to the retromandibular vein, indicated by the red arrow. (B) Depiction of the main trunk, highlighted by the white arrow, curving posteriorly towards the tragus. (C) The white arrow shows the branches of the facial nerve extending anteriorly across the tumor's surface. (D) The facial nerve and its branches following the excision of the tumor.

Reviewer 1 Comments

This article presents a case study involving a 75-year-old patient with a parotid gland lesion, highlighting the importance of facial nerve preservation during a parotidectomy. While dealing with parotid lesions, the surgical team encountered a unique anatomical aberration that deviated from the normal trajectory of the facial nerve. Consequently, they needed to employ alternative surgical techniques, transitioning from conventional anterograde dissection to a retrograde approach. This article describes a surgical experience characterized by flexibility and accuracy. It highlights the expertise required for parotid surgery, allowing readers to understand its intricate nature. Therefore, readers can gain both a deeper understanding and increased respect for the balance between surgical skill and unexpected obstacles. In this context, every choice is significant, and safeguarding the facial nerve is a primary goal. I recommend the article for publication due to its significant advantages; however, there are some issues that need to be addressed before final approval.

  1. Your introduction emphasizes the potential complexities involved in maintaining the facial nerve during a parotidectomy. Could you provide a more detailed exploration of the specific gaps or unresolved issues within the existing literature concerning these complications? Could you provide more concrete examples or clinical evidence to support this assertion? In my opinion, for example, preservation of the intricate facial nerve is of paramount importance during a parotidectomy. However, it becomes increasingly challenging when faced with variations in the size, position, and extent of the primary parotid lesion. Notably, both superficial and deep lobe parotid lesions disrupt the natural course of the facial nerve, presenting a formidable challenge to surgeons. Identification of facial nerve branches is essential during these procedures, especially when the nerve's trajectory is distorted by mass lesions within the gland. These lesions are often benign and predominantly affect the superficial lobe. Consequently, procedures like superficial or partial superficial parotidectomy carry a practical risk of post-operative facial paresis, with branches such as the marginal mandibular being particularly susceptible to injury. Minimizing this avoidable complication hinges on meticulous dissection, nerve monitoring, effective hemostasis, and the ability to locate the facial nerve trunk and its branches at the optimal moment during surgery. Nevertheless, the successful delineation of the facial nerve trunk is contingent upon recognizing its landmarks, which can be obscured by various pathological conditions, thus increasing the complexity of the task [Medeni Med J 2021;36(1):36–43]. The points outlined above can be instrumental for authors in offering elucidation on the precise facets that their study aimed to investigate, some of which may remain unresolved.
    ResponseThank you, please find appended our changes in direct response to each valuable point of feedback for this submitted manuscript. We have added a summary of the above points from Lines 28-33.
     
  2. For patients presenting with neck masses, a standard otorhinolaryngoscopy is considered an essential component of the comprehensive physical examination. Nevertheless, the article overlooks this aspect of the physical examination. The authors are therefore kindly requested to include this pertinent information to provide a comprehensive description of the physical examination findings in the manuscript.
    ResponseThank you for your comment. The nasoendoscopy findings have been included in the case presentation.
     
  3. During the initial CT scan, it was discovered that there was a superficial mass on the right side of the neck. However, the subsequent surgical procedure revealed a large tumor measuring 6 cm in size in the anterior portion of the right superficial parotid lobe, extending into the deep lobe. Your Discussion section notes that only 69% of radiological predictions about facial nerve position are reliable. Differences like these could make it challenging for surgeons to devise effective surgical strategies for dealing with parotid tumors. I think it's crucial to delve deeper into this matter in the Discussion section to enhance readers' understanding of the possible consequences of these variations on clinical decision-making.
    ResponseThank you for your comment. This has been enhanced in Lines 116-119.

Reviewer 2 Comments

The study presents an in-depth analysis of a 75-year-old patient diagnosed with a parotid gland lesion, emphasizing the importance of facial nerve preservation during a parotidectomy. During the surgical intervention for the parotid lesion, the team observed an uncommon anatomical deviation that significantly deviated from the conventional facial nerve course. Consequently, this observation necessitated an adjustment in their surgical approach, leading them to transition from anterograde dissection to retrograde dissection. Despite its critical insights into the interaction between surgical expertise and unexpected challenges in parotid surgery, the case report may not be accepted for publication in its current form. There may be some concerns that need to be addressed further.

  1. The surgical approaches to benign and malignant parotid tumors differ significantly. Benign tumors, with an emphasis on preserving gland function and facial nerves, are usually treated with a superficial parotidectomy. Conversely, malignant tumors demand more aggressive interventions, potentially necessitating a total parotidectomy, along with potential facial nerve sacrifice, to ensure complete excision. Lymph node dissection, infrequently required in benign cases, becomes a standard consideration when addressing malignancies with metastatic potential. The article references a follow-up CT scan revealing interval enlargement of the mass situated within the superficial parotid gland, characterized by patchy enhancement suggesting a low-grade parotid malignancy. An imperative inquiry arises regarding whether a frozen section biopsy was conducted to definitively ascertain the nature of the tumor (benign or malignant) and guide the subsequent surgical strategy. Clarifying this aspect of the patient's diagnostic and treatment journey would enhance the comprehensiveness of the article's clinical presentation.
    ResponseThank you for your comment. Intraoperative frozen section was not performed, given that pre operatively the suspicion was for a low-grade malignancy at worst. There was no suggestion of nodal involvement on the CT neck as well, hence we would not have performed a prophylactic neck dissection for the patient in this particular scenario. However, we agree that the inclusion of this piece of information would indeed improve the comprehensiveness of the clinical presentation and as such we have incorporated it into our article (Lines 63-66).
     
  2. In a recent study by Maddalozzo et al. (Laryngoscope Investig Otolaryngol 2019;4(5):550-553), the research demonstrated that deep lobe lesions could significantly alter the course of the extratemporal facial nerve, causing a lateral displacement of the nerve trunk and pes anserinus to a more superficial position. This distortion complicates the accurate identification of the main facial nerve trunk based on traditional landmarks. Nevertheless, various well-established anatomical landmarks for locating the facial nerve trunk exist. For instance, during anterograde dissection of the facial nerve, surgical landmarks such as the tragal pointer, posterior belly of the digastric muscle, tympanomastoid suture line, and the stylomastoid artery have been employed (Medeni Med J 2021;36(1):36–43). While it may not always be feasible to visualize all these landmarks due to factors like lesion nature and size, it would be valuable to know if surgeons attempted to utilize alternative landmarks to pinpoint the facial nerve trunk during the surgical procedure.
    ResponseThank you for the clarification, the above standard surgical landmarks were used, with the exception of the stylomastoid artery, as that is not our institution’s practice. This has been indicated in Lines 54-55.

Reviewer 3 Comments

This paper details a notable case of a 75-year-old patient who initially exhibited a parotid mass, which subsequently manifested as a potential low-grade malignancy over three years. Notably, the patient exhibited displacement of the facial nerve main trunk due to the parotid lesion. The authors provide a detailed analysis of the complexities and challenges associated with anomalous facial nerve anatomy. This case study emphasizes the difficulties associated with managing parotid gland anomalies, making it a valuable resource for medical research and discourse. I believe it deserves to be published if it undergoes a few minor revisions.

  1. I propose that the authors provide a well-defined rationale for presenting the case in the second paragraph of the Introduction section. Below, you will find my suggested revision: Presented here is a compelling case study that exemplifies the challenges posed by aberrant facial nerve anatomy resulting from a parotid lesion. In this article, we discuss how the use of retrograde dissection, as opposed to traditional anterograde dissection, enabled us to protect the integrity of the facial nerve while effectively addressing the parotid lesion in this case.
    ResponseThank you for your comment. We have revised our introduction to incorporate the points above in Lines 33-36.
     
  2. Would it be possible for you to provide some information about the postoperative care, including follow-up assessments and any long-term results associated with the patient's facial nerve function because of the surgery?
    ResponseThank you, this has been included in lines 67-70.
     
  3. During the surgical procedure, there were notable challenges related to facial nerve anatomy. Could you discuss any potential errors or difficulties encountered during the surgery and how they were managed? Additionally, what valuable lessons were learned from this case that could be applied to similar surgical scenarios in the future to ensure patient safety and optimal outcomes?
    ResponseThank you, this has been edited in Lines 54-59.  In addition, we have included an expanded description of surgical pearls in such cases in Lines 99-103.

Editorial Comments

In adherence to our publication's established standards, we respectfully ask for the inclusion of each author's academic and professional credentials, which may encompass designations such as MD or MD, PhD. The inclusion of these credentials enables readers to evaluate the authors' expertise and professional qualifications, thereby augmenting the comprehensive credibility and integrity of the published material.
ResponseThank you, the authors' credentials have been included.