Prevalence of Facial Paralysis After Surgical Treatment of Malignant Tumors of the Parotid Gland: A Systematic Review

ABSTRACT

Objective:  To estimate the prevalence of facial paralysis in patients with malignant parotid tumors who underwent parotidectomy.

Material and Methods:  The method employed was a systematic review, with a search conducted in the following databases: PubMed, Embase, Scopus, Web of Science, and LILACS. Grey literature from Google Scholar and ProQuest Dissertations and Theses was also used. The included studies were observational, performed with patients with malignant parotid tumors, diagnosed from the histopathological examination of the gland, with permanent or transient facial paralysis, verified by clinical examination, as a result of surgical treatment for the neoplasm.

Results:  Among the 2156 studies identified, 16 were selected for this systematic review. The prevalence of facial paralysis after parotidectomy due to malignancy varied according to the type of facial paralysis, the size of the tumor, the kind of parotidectomy performed, the presence of preoperative facial paralysis, and the need for adjuvant radiotherapy.

Conclusion:  The prevalence of facial paralysis after parotidectomy due to malignancy ranged from 9.09% to 100% among the studies.

Keywords:
Parotid Neoplasms; Facial Paralysis; Facial Nerve; Surgery.

Introduction

The parotids are the largest salivary glands in the body, presenting an intimate anatomical relationship with structures such as the facial nerve. Most salivary gland neoplasms originate in the parotid gland, with 80% being benign and 20% malignant [¹]. In this context, the estimated number of new cases of salivary gland cancer in 2022, in both sexes and in all age groups, was 55,083 worldwide. In Brazil, in 2022, there were 1,742 new cases, being the sixth country with the highest incidence, and 487 deaths from parotid malignancies, occupying the eleventh place in the world in mortality from the cause [²].

The appropriate management of parotid cancer is based on histopathological diagnosis, and the primary therapeutic choice is the surgical approach. Chemotherapy and radiotherapy are reserved for unresectable cases [¹,³]. Surgical intervention of malignant tumors of the parotid gland can result in injury and dysfunction of the facial nerve, depending on the staging, grade, and location of the tumor [¹]. Thus, parotidectomy for malignancies can result in an outcome of facial paralysis, which, although not life-threatening, compromises your quality of life, being associated with anxiety, stress, and depression [⁴].

Knowledge of the prevalence of facial paralysis after parotidectomy for malignant parotid tumors is necessary to understand the impact of the problem on the population and to evaluate the factors that are associated with such involvement. Thus, the present study aimed to estimate the prevalence of facial paralysis in patients with malignant parotid tumors.

Material and Methods

Protocol and Registration

This systematic review was conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [⁵,⁶]. The protocol of this review is registered on the International Prospective Register of Systematic Reviews (PROSPERO) website with the registration number CRD42022316679.

Inclusion Criteria

Observational studies conducted with patients with malignant parotid tumors, diagnosed from histopathological examination of the gland, with permanent or transient facial paralysis, verified by clinical examination, as a result of surgical treatment for the neoplasm.

Exclusion Criteria

The exclusion criteria for the present study were: (1) Studies that have only patients with malignant parotid tumors undergoing other treatment regimens that are not associated with tumor resection surgery; (2) Studies that did not present surgical interventions in the parotid gland; (3) Studies with no outcome; (4) Studies that do not report facial paralysis associated with surgery for malignant parotid tumor; (5) Studies that did not present data on the frequency, incidence, or prevalence of facial paralysis after surgical treatment of malignant parotid neoplasm; (6) Review studies, letters, summaries, personal opinions, and case reports; (7) Studies that were not fully available; (8) Studies that do not differentiate the prevalence of transient from permanent facial paralysis; (9) Studies that do not report the histopathological diagnosis of all patients; (10) Studies that do not report the type of parotidectomy to which the patients were submitted; (11) Studies whose reported data differ in their description.

Data Sources

The search strategy was adapted to all the databases used: PubMed, Embase, Scopus, Web of Science, and LILACS. A complementary search in the gray literature was also carried out, using Google Scholar and ProQuest Dissertation and Thesis. There was also a provision in our protocol to use OpenGrey as a complement to the gray literature; however, this database was not available during the period in which the search was carried out. The first search was conducted in the databases on May 12, 2022, and was updated on January 3, 2023, and February 25, 2024. For the organization of the studies that resulted from the search, import, and export of articles, and the removal of duplicate articles, Rayann Systems Inc. was used [⁷].

Selection of Studies

The selection of included studies was carried out in two phases: (1) title reading and abstract analysis; (2) reading the full text. Two independent reviewers (NCLD and FRNS) checked the studies in these two phases, applying the eligibility and exclusion criteria. The divergences were resolved by a third reviewer (AMCL). In cases where studies with essential data were not mentioned, an attempt should be made to contact the author to clarify any doubts.

Data Extraction

Data were extracted from a standardized list that includes: author, year of publication, country, type of study, sample size, age group, gender, preoperative facial paralysis, type of parotidectomy, facial nerve resection and reconstruction, postoperative radiotherapy, and prevalence of facial paralysis. The first reviewer (NCLD) collected information from the studies selected from the pre-established list. The second reviewer (FRNS) checked the information chosen by the first author. Doubts and divergences were resolved through consultation with the third reviewer (AMCL).

Risk of Bias

The analysis of risk of bias was performed using the Joanna Briggs Institute (JBI) Critical Evaluation of Prevalence Studies tool [⁸]. Two review authors (NCLD and FRNS) independently analyzed and rated the risk of each study as 'high', 'low', or 'unclear'. The third reviewer (AMCL) was consulted in cases of doubt.

Summary of the Data

Data synthesis was performed by tabulating the items requested in a pre-defined list.

Summary of Measures

The prevalence of facial paralysis in patients with malignant parotid tumors undergoing surgical treatment was expressed as the mean percentage and standard deviation of the mean.

Results

Selection of Studies

A total of 3851 studies were obtained from the databases. In addition to these results, 100 studies were taken from Google Scholar and 01 study from ProQuest Dissertation and Thesis. Those articles were exported to Rayann Systems Inc., where 1871 duplicates were detected and manually removed. The first phase of selection of studies began, with 2081 selected to be submitted to the reading of the title and abstract. Out of this total, 326 studies were selected for a second phase of selection, which involved a complete reading of each study. After a thorough review of the selected articles, 16 articles were included in the analysis [⁹-²⁴].

The selected articles had the year of publication within the period from 1999 to 2023. As for the countries in which they were carried out, the following were considered: South Korea (n=4) [¹⁰,¹³,¹⁷,²²], United States of America (n=3) [¹⁵,²⁰,²⁴], China (n=2) [¹²,¹⁴], Italy (n=2) [⁸,²⁰], India (n=1) [¹¹], England (n=1) [¹⁹], Chile (n=1) [²³], Portugal (n=1) [¹⁶] and Egypt (n=1) [¹⁸]. The type of study conducted was retrospective observational in fifteen articles [⁹,¹⁰,¹²-²⁴] and prospective observational in one [¹¹]. Regarding the patient samples, the number of patients ranged from 4 to 256. Of the samples, there was a mean age of 13.7 years to 80.6 years, with a total age range between 3 and 92 years. Data from the studies reported above are in Tables 1 and 2.

Table 1
Synthesis of the results from each study, categorized by study type, sample size, type of parotidectomy, and prevalence of facial paralysis.

Author/ Year / Country	Study	Sample	Type of Parotidectomy		Prevalence of Facial Paralysis
					N (%)
Pecorari et al./ 2023/ Italy [9]	RO	18	Superficial: 3 / Total: 15	Transient: 5 (27.70) / Permanent: 5 (27.70) / Total: 10 (55.40)
Lee et al. / 2023/ South Korea [10]	RO	180	Partial: 27 / Superficial: 66 / Total: 72 / Radical: 15	Transient: 16 (8.88) / Permanent: 19 (10.55) / Total: 35 (19.43)
Bhardwaj et al. / 2020/ India [11]	AFTER	4	Superficial: 1 / Total: 3	Transient: 2 (50.0) / Permanent: 2 (50.0) / Total: 4 (100.0)
Li et al. / 2020/ China [12]	RO	16	Total: 10 / Subtotal: 6	Transient: 3 (18.75) / Permanent: 1 (6.25) / Total: 4 (25.0)
Park et al. / 2019/ South Korea [13]	RO	256	Conservative: 110 / Total: 146	Transient: 35 (13.67) / Permanent: 5 (1.95) / Total: 40 (15.62)
Wu et al. / 2019/ China [14]	RO	108	Partial: 9 / Superficial: 8 / Total: 7 / Local extensive: 84	Transient: 22 (20.37) / Permanent: 15 (13.88) / Total: 37 (34.25)
Dombrowski et al. / 2019/ USA [15]	RO	11	Superficial: 7 / Total: 2 / Revision: 2	Transient: 2 (18.18) / Permanent: 0 (0.0) / Total: 2 (1818)
Correia-Sá et al. / 2016/ Portugal [16]	RO	27	Superficial: 8 / Total: 11	Transient: 9 (33.33) / Permanent: 9 (33.33) / Total: 18 (66.66)
Chang et al. / 2015/ South Korea [17]	RO	98	Superficial: 38 / Total: 36 / Radical: 24	Transient: 15 (15.30) / Permanent: 3 (3.06) / Total: 18 (18.36)
El-Shakhs et al. / 2013/ Egypt [18]	RO	11	Total: 11	Transient: 0 (0.0) / Permanent: 1 (9.09) / Total: 1 (9.09)
Henney et al. / 2009/ England [19]	RO	6	Superficial: 3 / Total: 3	Transient: 5 (83.33) / Permanent: 1 (16.66) / Total: 6 (100.0)
Gomez et al. / 2009/ USA [20]	RO	35	Subtotal: 21 / Total: 14	Transient: 13 (37.14) / Permanent: 10 (28.57) / Total: 23 (65.71)
Marchesi et al. / 2006/ Italy [21]	RO	24	Superficial Total: 20 / Total Deeh: 4	Transient: 4 (16.66) / Permanent: 3 (12.50) / Total: 7 (29.16)
Lim et al. / 2005/ South Korea [22]	RO	43	Conservative: 43	Transient: 5 (11.62) / Permanent: 0 (0.0) / Total: 5 (11.62)
Aguirre and Vent/ 2004/ Chile [23]	RO	8	Superficial: 2 / Total: 6	Transient: 0 (0.0) / Permanent: 7 (87.50) / Total: 7 (87.50)
Witt/ 1999/ USA [24]	RO	5	Partial Superficial: 5	Transient: 2 (40.0) / Permanent: 0 (0.0) / Total: 2 (40.0)

Table 2
Synthesis of the results from each study by age group, gender, preoperative facial paralysis, facial nerve resection, facial nerve reconstruction, and postoperative radiation therapy.

Author	Age Group	Gender	Preoperative Facial Paralysis	Facial Nerve Resection/ Reconstruction	Postoperative Radiotherapy
Pecorari et al. [9]	Av: 80.6	M: 8 / F: 10 / M/F: 1.25:1	1	1/-	12
Lee et al. [10]	Av: 60 / Int: 11-92	M: 102 / F: 78 / M/F: 1.3:1	1	-/-	106
Bhardwaj et al. [11]	Av: 40.1*	M/F: 1.54:1*	-	2/-	-
Li et al. [12]	Av: 13.7 / Int: 3-18	M: 8 / F: 8 / M/F: 1:1	0	1/1	16
Park et al. [13]	Mdn: 50 / Int: 8-82	M:128 / F: 128 / M/F: 1:1	4	-/-	135
Wu et al. [14]	Av: 41.7 / Int: 18-79	M: 48 / F: 60 / M/F: 1:1.25	3	3/3	108
Dombrowski et al. [15]	Mdn: 12.4 / Int: 9.8-19.2	M: 3 / F: 8 / M/F: 1:2.3	-	1/1	5
Correia-Sá et al. [16]	Av: 60.19	M: 15 / F: 12 / M/F: 1.25:1	-	*/*	18
Chang et al. [17]	Av: 49.7 / Int: 12-88	M: 56 / F: 42 / M/F: 1.33:1	13	-/-	55
El-Shakhs et al. [18]	Av: 49	M: 6 / F: 5 / M/F: 1.2:1	-	1/-	5
Henney et al. [19]	Mdn: 66.5 / Int: 16-88	M/F: 1:1*	-	-/-	-
Gomez et al. [20]	-	M: 18 / F: 17 / M/F: 1.05:1	1	12/5	22
Marchesi et al. [21]	Av: 51* / Int: 27-72*	M/F: 1.04:1*	-	2/-	-
Lim et al. [22]	Av: 55 / Int: 8-84	M: 16 / F: 27 / M/F: 1:1.68	0	-/-	10
Aguirre and Vent [23]	Int: 18-80	M: 4 / F: 4 / M/F: 1:1	-	4/-	7
Witt [24]	Av: 52* / Int: 18-80*	M/F: 1:1.03*	-	-/-	-

• -= Not informed;
• ^*
  = Not distinguished from other data; Int = Interval; Av= Average; Mdn= Median; M= Male; F = Female; M/F= Proportion between male and female in the study;

Risk of Bias in Studies

Five studies were classified as having low risk of bias [¹¹,¹²,¹⁴,²⁰,²¹], eight as moderate risk of bias [⁹,¹⁰,¹³,¹⁵-¹⁸,²²], and three as high risk of bias [¹⁹,²³,²⁴]. The risks of bias in the studies, as detailed in Figures 1 and 2 [⁸] according to the Joanna Briggs Institute's critical evaluation tool for prevalence studies, are outlined below.

Figure 1
Risk of bias chart: judgments on each risk of bias item presented as percentages across all included studies.

Figure 2
Risk of bias summary: judgments on each risk of bias item for each included study.

Summary of Measures

Based on the data extracted from the studies, the mean values were calculated along with the standard deviation of the studies. The mean total post-parotidectomy facial paralysis due to malignant parotid tumor was 13.68 cases, with a standard deviation of 12.91. Specifying the type of involvement, the mean transient facial paralysis obtained was 8.62 cases, with a standard deviation of 9.16. Permanent facial paralysis had a mean of 5.06 cases, with a standard deviation of 5.48.

Discussion

The present study gathered sixteen articles totaling 850 patients to evaluate the prevalence of facial paralysis after parotidectomy for parotid malignancy. The justification for the importance of knowing this data is that facial paralysis is reported as one of the most feared complications of this surgery [²⁵]. Along with this, it can also lead to psychological repercussions, such as anxiety, depression, and stress [²⁶,²⁷].

The included studies respected a homogeneous ratio between men and women, with four with an equal distribution between the number of men and women [¹²,¹³,¹⁹,²³], and the rest did not exceed a proportion of 1:2. Regarding the age group, only two studies were carried out only in the pediatric population [¹²,¹⁵], resulting in 25% (4 cases) 18.18% (2 cases), most of which were transient facial paralysis. However, such demographic data as age group and gender could not be better analyzed, as the studies did not establish a direct correlation between the number of cases of postoperative facial paralysis and such data, being only described in the initial sample presented.

Regarding transient facial paralysis, prevalence rates ranged from 0% to 83.33%, while permanent facial paralysis had results ranging from 0% to 87.5% of prevalence. These data differ in the literature for many reasons, one of the main ones being the type of surgery to which the patient was submitted within his sample and the size of the sample. Due to this, the standard deviation of the mean number of cases obtained in the present study was high, indicating a high level of data variability. The prevalence of facial paralysis is more associated with more extensive surgeries, such as total parotidectomy, mainly when the tumor is located in the deep lobe of the gland [¹³,¹⁹,²¹,²⁸].

The variability in facial paralysis rates relative to the surgical type also depends on the type of facial paralysis. This is because more invasive surgeries have greater manipulation of the facial nerve. Regarding superficial parotidectomy, partial parotidectomy progresses with tumor resection with an attempt to preserve the facial nerve [²⁹-³¹]. Even if there is less facial nerve affection, there is a risk of transient facial paralysis, which can occur due to ischemic, thermal, or blunt surgical trauma [²¹]. Witt [²⁴] performed only partial superficial parotidectomy in his sample of five patients, obtaining a rate of 40% (2 patients) of transient facial paralysis and no cases of permanent facial paralysis. In addition, Lim et al. [²²] submitted their 43 patients to conservative parotidectomy, verifying a rate of 11.62% (5 patients) of transient facial paralysis and no cases of permanent facial paralysis. Both studies, in absolute terms, reported a similar small number of patients with facial nerve involvement, and the prevalence rate diverged due to differences in sample size.

Total parotidectomy, on the other hand, performs a complete dissection of the facial nerve bilaterally, so that tumor resection can be performed [³²,³³]. Park et al. [¹³] conducted a study with 256 patients, finding a rate of 13.67% for transient facial paralysis (35 cases, four of which were due to conservative parotidectomy and 31 due to total parotidectomy) and 1.95% for permanent parotidectomy (5 cases, all due to total parotidectomy). In addition, El-Shakhs et al. [¹⁸] and Henney et al. [¹⁹], despite having a small sample, eleven and six, respectively, corroborated the literature analyzed by presenting the totality of permanent facial paralysis being caused by total parotidectomies. The data reported in the present study and in the literature show that the rates of permanent facial paralysis are caused mainly by more extensive parotidectomy [³²,³³].

In addition to greater manipulation of the facial nerve during surgery, in the presence of tumors with invasion of the facial nerve, there is an indication of neural sacrifice [³²]. Due to the aesthetic-functional impairments associated with such management, nerve reconstruction is essential, since it obtains acceptable levels of facial function [³³]. Not all of the studies analyzed reported whether the facial nerve was sacrificed, and of those that did report, few reported how many patients underwent facial nerve reconstruction and the participation of this population in the absolute rates of facial paralysis. Li et al. [¹²] performed facial nerve sacrifice in one patient, with subsequent reconstruction, but he represented the only patient in the sample to present permanent facial paralysis. Similarly, Gomez et al. [²⁰] reported that the sacrifice of the facial nerve or some main branch occurred in 12 cases, with reconstruction in 5 cases, resulting with permanent facial paralysis in all patients within this sample.

A clinical indication sometimes used as a predictor for tumor involvement and subsequent need for facial nerve sacrifice is preoperative facial paralysis [³⁴]. Studies show preoperative facial paralysis as a good predictor of tumor invasion, need for facial nerve sacrifice, and postoperative facial paralysis [²⁸,³²]. In our sample of studies, not all reported the number of patients who experienced preoperative facial paralysis, so we were unable to establish a direct correlation between this data and the sacrifice of the facial nerve and its resulting paralysis.

In addition, postoperative radiotherapy can be performed in cases of high-grade malignant tumors, advanced T stage, perineural invasion, positive margins, and regional metastasis [³⁵]. Because of the factors that indicate the adjuvant procedure, such patients were associated with worse outcomes [³⁶]. Although 12 studies mentioned the number of patients undergoing postoperative radiotherapy (totaling 499 patients) [⁹,¹⁰,¹²,¹⁴-¹⁸,²⁰,²²,²³], there was no report of the relationship between patients with facial paralysis who underwent this therapy in relation to those who did not. It was also not possible to identify the relationship between the prevalence of postoperative facial nerve palsy and this variable.

The limitations found by this study were related to the divergences in standardization between the studies. Although 326 were selected for the whole reading phase, only 16 met the inclusion criteria without any exclusion criteria. The main reasons for exclusion were: failure to differentiate between permanent and transient facial paralysis rates, not containing data on surgical procedures for the entire sample of patients, not differentiating the prevalence of facial paralysis between benign and malignant samples, and not differentiating the prevalence of facial paralysis according to the salivary gland affected. In addition, other factors that contributed to the limitations of the study were the divergence between the sample size and the lack of specification in some studies on the surgical procedure to which each patient with facial paralysis was submitted, as well as facial nerve resection, postoperative radiotherapy, and preoperative facial paralysis.

Conclusion

The prevalence of facial paralysis after malignant parotidectomy ranged from 9.09% to 100% among the studies. Factors that influenced the increase in prevalence were: tumor size, type of parotidectomy performed, preoperative facial paralysis, and need for adjuvant radiotherapy. The present study suggests a greater standardization of studies by reporting the data found in greater detail on the type of surgery and preoperative and postoperative findings, so that future meta-analyses can be conducted for a more solid estimate of facial paralysis after parotidectomy for malignant tumors of the parotid gland.

• Financial Support
  Scientific initiation scholarship granted by the Federal University of Piauí.

Acknowledgments

The authors thank all participants for completing the study and the Federal University of Piauí for encouraging the research.

Data Availability

The data used to support the findings of this study can be made available upon request to the corresponding author.

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Edited by

• Academic Editor:
  Alidianne Fábia Cabral Cavalcanti

Publication Dates

• Publication in this collection
  08 Dec 2025
• Date of issue
  2026

History

• Received
  30 Aug 2024
• Reviewed
  21 Feb 2025
• Accepted
  06 Mar 2025