Meta-Analysis to Evaluate the Efficacy of Sternocleidomastoid Muscle Flap as a Reconstruction Modality in Prevention of Frey’s Syndrome Following Parotidectomy

Abstract

Background

One of the commonest complications following parotidectomy is Frey’s syndrome (FS). The use of sternocleidomastoid muscle (SCM) flap to prevent FS is controversial. Hence, this study has been designed to compare the effect of SCM flap with no reconstruction in prevention of FS following parotidectomy.

Methodology

An exhaustive literature search was conducted in July 2019. Studies focusing on sternocleidomastoid flap following parotidectomy were included in the meta-analysis. A random effects model was used to generate pooled estimates. Odds ratio with a 95% confidence interval was calculated for subjective symptoms and objective test.

Results

A total of 125 studies were identified, out of which 17 studies were recruited in the meta-analysis. Sixteen studies were analyzed for the subjective symptoms, and ten were analyzed for the objective signs. There was no statistically significant difference in the occurrence of FS with the use of SCM flap on objective analysis. However, the subjective analysis showed a statistically significant reduction in FS following reconstruction with SCM flap after parotidectomy.

Conclusion

The present meta-analysis suggests that the use of SCM flap following parotidectomy has no effect in reducing the incidence of Frey’s syndrome.

Introduction

Parotid gland is affected by majority of benign and malignant salivary gland tumors. The surgical techniques for management of such pathologies have been evolved with the course of time, and today several techniques have been advocated. However, parotidectomy, either superficial or total depending upon the extent of the tumor, is considered to be the standard treatment. Parotidectomy has a low recurrence rate but it leads to a few postoperative complications which include temporary or permanent injury to facial nerve, loss of ear lobule sensation, cosmetic deformity and Frey's syndrome (FS). These complications significantly affect the quality of life of the patients.

FS is a potential ramification of parotidectomy with a varying incidence of 6% to 96% [1]. Frey in 1923, first identified the notability of the auriculotemporal nerve in the pathogenesis of this condition [2]. This syndrome is a classic triad consisting gustatory sweating, warming and flushing over the preauricular and temporal areas. Its presence may cause social embarrassment and isolation. Numerous medicinal and surgical treatments have been tried, with varying degrees of success. Application of antiperspirant and anticholinergic agents over the skin, disruption of regenerating fibers and interruption of parasympathetic fibers have been tried but once the syndrome is established, it becomes difficult to eliminate the symptoms. Hence, the approach has been shifted to prevention of the condition by interposition of barriers between the parotid bed and skin flap.

Interpositioning of sternocleidomastoid muscle flap (SCMMF) is one of the numerous techniques which are reported in the literature that not only prevents the gustatory sweating but also corrects the postoperative contour deformity [3–5]. However, the studies comparing the efficacy of SCMMF in the prevention of FS show contradictory results [5–9]. Hence, this meta-analysis was conducted with an aim to evaluate the effectiveness of SCMMF in the prevention of FS following parotidectomy.

Methodology

Search Strategy

An exhaustive literature search was conducted on online databases like PubMed, Medline, Cochrane, Scopus and Google Scholar in July 2019. Grey literature was also searched for any unpublished studies. Keywords like parotidectomy, Frey’s Syndrome, sternocleidomastoid muscle flap, parotid gland surgery, gustatory sweating were used for the search purpose. Boolean operators ‘AND’ and ‘OR’ were used for expanded search of relevant articles. References of the relevant articles were also explored to identify other articles.

Selection of Studies

After initial search, the title and abstracts of all the articles were reviewed. The articles dealing with operative procedures for prevention of FS following parotidectomy were selected for detailed evaluation. After detailed evaluation, studies comparing the effect of SCMMF with that of no flap on the occurrence of FS in cases of partial or total parotidectomy for benign or malignant tumor were included in the meta-analysis. The articles of English language were only recruited. Studies with incomplete data or which included patients with history of previous radiotherapy or previous surgery in parotid region were excluded. The outcome of the analysis was Frey’s Syndrome. Both the subjective as well as objective measures of the outcome were analyzed individually.

Data Extraction and Management

The data of the included studies like sample size, surgical procedures, patient characteristics, treatment group characteristics and details of outcome were extracted. For study characteristics, we included publication details (author, year of publication), study period, and location. The methodologic quality of each study was noted for assessment of risk of bias in the included studies. Risk assessment was done in seven risks of bias domains: 1. Randomization methods, 2. Allocation concealment, 3. Blinding of participants and personnel, 4. Blinding of outcome assessment, 5. Incomplete outcome data, 6. Selective reporting and 7. Other bias. Each study was independently assessed for risk of bias.

Statistical Analysis

We performed a meta-analysis for SCMMF compared to no flap in prevention of occurrence of FS. We calculated odd’s ratio with 95% confidence interval for dichotomous variables by using a random effects model in Review Manager, Version 5.3, Cochrane Collaboration. Individual analysis was done for both subjective and objective outcomes. The heterogeneity was evaluated with estimates of effect using Chi² test and I² statistics. We considered heterogeneity to be statistically significant if the P value was less than 0.05.

Results

Search Results

The database searches yielded 125 results. After screening of these abstracts, 101 articles were excluded and 24 full text articles were assessed for possible inclusion in the analysis. We excluded eight out of 24 full text articles due to language constraints and incomplete data and 16 articles were included in the analysis. Out of these 16 articles, 14 were included in subjective analysis and ten were included in objective analysis. (Fig. 1).

Fig. 1.

Flow diagram of study selection process

Characteristics of the Included Studies

We included a total 16 studies, characteristics of which are highlighted in Table 1. Table 2 highlights the study outcomes of included studies.

Table 1.

Characteristics of included studies

S. No	Author and location	Age (years)	Gender (M/F)	Follow-up	No. of cases		Outcomes		Methods of assessment
							Cosmetic impairment	Frey’s syndrossme
					SCM flap	No flap
1	Asal K et al. [3] Turkey	29-71 years	12/12	9–48 months	12	12	Yes	Yes	Objective and subjective
2	Casler and Conley [4] San francisco	Not Specified	Not Specified	24 months	16	104	No	Yes	Subjective
3	Demirci U et al. [5] Turkey	32–58 years	16/27	6 months	22	21	No	Yes	Subjective
4	Fee et al. [6] California	Not Specified	6/18	3–60 months	15	9	Yes	Yes	Objective and subjective
5	Filho et al. [7] Brazil	60–67 years	22/21	12–90 months	24	19	No	Yes	Objective and subjective
6	Gooden EA et al. [8] Canada	56–63 years	8/18	> 12 months	13	13	Yes	Yes	Objective and subjective
7	Grosheva et al. [9] Germany	Not Specified	74/56	6–24 months	7	51	No	Yes	Objective and subjective
8	Guntinas Lichius [10] Germany	14–87 years	300/310	6–26 months	391	169	Yes	Yes	Objective
9	Kerawala CJ et al. [11] England	26–81 years	13//23	12–60 months	21	15	Yes	Yes	Objective and subjective
10	Kim et al. [12] Michigan	Not Specified	Not Specified	12–57 months	9	10	Yes	Yes	Subjective
11	Kornblut et al. [13] Germany	Not Specified	Not Specified	12–72 months	35	35	No	Yes	Objective and subjective
12	Kumar J et al. [14] India	10–60 years	29/19	6 weeks-12 months	24	24	Yes	Yes	Subjective
13	Liang KY et al. [15] England	26–67 years	14/16	1–30 months	15	15	Yes	Yes	Subjective
14	Manola M et al. [16] Italy	32–77 years	49/50	< 24 months	12	20	Yes	Yes	Objective and subjective
15	Rustemeyer et al. [17] Germany	39–61 years	Not specified	2–172 months	203	169	No	Yes	Subjective
16	Sood et al. [18] Nottingham	29–72 years	Not specified	23–82 months	11	11	No	Yes	Objective and subjective

Table 2.

Outcome of selected studies

Sr. No	Author	Patients with SCM flap			Patients with No flap
		Total patients	Subjective FS	Objective FS	Total patients	Subjective FS	Objective FS
1	Asal K et al. [3]	12	0	0	12	0	6
2	Casler and Conley [4]	16	2	–	104	49	–
3	Demirci U et al. [5]	22	0	–	21	4	–
4	Fee et al. [6]	15	2	3	9	4	2
5	Filho et al. [7]	24	0	0	19	9	7
6	Gooden EA et al. [8]	13	4	4	13	3	4
7	Grosheva et al. [9]	7	–	4	51	–	24
8	Guntinas Lichius [10]	391	–	17	169	–	5
9	Kerawala CJ et al. [11]	21	8	19	15	9	11
10	Kim et al. [12]	9	2	–	10	5	–
11	Kornblut AD et al. [13]	35	14	34	35	9	33
12	Kumar J et al. [14]	24	0	–	24	2	–
13	Liang KY et al. [15]	15	1	–	15	0	–
14	Manola M et al. [16]	12 + 23	0 + 2	1 + 2	20 + 15	4 + 9	7 + 11
15	Rustemeyer et al. [17]	203	49	–	169	37	–
16	Sood et al. [18]	11	0	2	11	2	9

Analysis Result

The results of this meta-analysis are represented in Figures 2 and 3. Figure 4 shows the measure of heterogeneity in the analysis, both subjective as well as objective, of the included studies. Meta-analysis of subjective outcomes of the study revealed that SCMMF flap has statistically significant less incidence of FS than that of no reconstruction. (OR = 0.36, 95% CI 0.17–0.76, p = 0.007; I² = 61%). Meta-analysis of objective outcomes of the study revealed that there is no statistically significant difference in the occurrence of FS in both the groups. However, the results favor the use of SCMMF. (OR = 0.40, 95% CI 0.14–1.13; p = 0.08, I² = 69%).

Fig. 2.

Forest plot of subjective outcomes

Fig. 3.

Forest plot of objective outcomes

Fig. 4.

Funnel plots of subjective and objective meta-analysis

Risk of Bias Assessment Result

Table 3 highlights the risk of bias assessment. Most of the studies have high risk of bias which might affect the result of the analysis.

Table 3.

Assessment of risk of bias in included studies

Studies	A	B	C	D	E	F	G
Asal K et al.	Unclear	Unclear	Low	Low	Low	Low	Low
Casler and Conley	High	High	Unclear	Unclear	Unclear	Unclear	Unclear
Demirci U et al.	Unclear	Low	Low	High	Low	Low	Low
Fee et al.	High	Unclear	Unclear	Low	Low	Low	Low
Filho et al.	High	Unclear	Unclear	Unclear	Low	Unclear	Low
Gooden EA et al.	High	High	Low	Low	Low	Unclear	Low
Guntinas Lichius et al.	High	High	High	High	Low	Unclear	Low
Kerawala CJ et al.	Low	Unclear	Low	Low	Low	Low	Low
Kim SY et al.	High	High	Unclear	Unclear	Low	Low	Low
Kornblut AD et al.	High	High	Unclear	Unclear	Low	Low	Low
Kumar J et al.	High	Unclear	Unclear	Unclear	Low	Low	Low
Liang KY et al.	High	High	Unclear	Unclear	Low	Low	Low
Manola M et al.	High	High	Unclear	Unclear	Low	Unclear	Low
Rustemeyer J et al.	High	High	Unclear	Unclear	Low	Unclear	Low
Sood S et al.	High	High	Unclear	High	Low	Low	Low

A = Randomization methods

B = Allocation concealment

C = Blinding of participants and personnel

D = Blinding of outcome assessment

E = Incomplete outcome data

F = Selective reporting

G = Other bias

Discussion

Frey’s Syndrome is one of the commonest complication following parotidectomy [19–21]. This syndrome is characterized by sweating, redness and warmth in preauricular region [22–25]. In 1927, the pathophysiology of FS was explained to be caused due to aberrant regeneration of auriculotemporal nerve fibers which go to the parotid gland passing through the facial nerve and innervate the sweat glands and blood vessels of the skin. This leads to the pathognomonic sweating and flushing of the parotid region during eating [26]. In the earlier times, the management involved use of topical and systemic medications, along with various adjunctive procedures like extirpating the involved tissues or interrupting the neural pathways to the involved tissues [27–35]. Symptoms were reduced following these modalities but they failed to achieve absolute success for long durations. Hence, to prevent FS, interpositioning some tissue between parotid bed and the skin is practiced. Various flaps used for this purpose are SCMMF, SMAS flap, temporoparietal flap, platysma, derma flaps, submandibular gland flap and vascularized dermis-fat grafts [11, 15, 36–43].

The SCMMF is most commonly used flap as it is easier to rotate and obliviates the need of another incision. It not only covers all the branches of facial nerve but also provides adequate bulk to compensate for the depression caused following gland resection. Furthermore, it has high vascularity minimizing the risk of necrosis and has a low risk of complications. Despite of so many advantages, use of SCMMF following parotidectomy is controversial. Some authors recommend it [3, 7, 16, 18]; on the other hand, others disagree [9–11, 13, 44]. Hence, it becomes imperative to support the surgical interventions regarding their effectiveness. Other than the effectiveness of the reconstruction modality in prevention of FS, other factors such as cost, restoration of post-operative contour deformity and operating time are also important to be taken into consideration [45].

The technique of SMAS flap was developed by Owsley [46]. The SMAS layer is the deep layer of the superficial cervicofascial fascia that includes the muscles related to facial expression. The SMAS flap is used to cover the surgical defect following parotidectomy and is sutured to the perichondrium of the external ear canal and sternocleidomastoid muscle [41]. There are numerous publications focusing on the efficacy of SMAS flap in prevention of FS following parotidectomy. However, there was lack of conclusive evidence to advocate the use of SMAS flap. In 2016, meta-analysis conducted by Dulguerov N et al. concluded that the use of SMAS flap is associated with a decreased incidence of FS following parotidectomy [47].

Use of temporoparietal fascia flap (TPFF) is also mentioned in the literature for creating a barrier between the parotid bed and superficial skin [38]. Unlike temporalis flap, the TPFF is a thin flap and does not produce any fullness over zygomatic arch when rotated over it. It is based on the superficial temporal vessels. Sometimes, ligation of superficial temporal artery during parotidectomy limits the use of this flap [37]. However, there is hardly any conclusive literature to support the use of this flap as an interpositioning material.

Wang et al. [48] first evaluated the effectiveness of Platysma muscle flap (PMF) following parotidectomy. They reported PMF to be effective in reducing the incidence of FS. Similarly, Hayashi et al. [49] recommended the use of PMF following parotidectomy. However, both the articles reported that the cases in which complete coverage could not be obtained, FS persisted. The technique for use of PMF is technique sensitive as the muscle is thin, and it is supposed to be elevated along with the underlying fat as various small vessels providing vascular supply to this flap pass through the underlying fat [49].

A few reports are present in the literature which were focused on the use of derma flaps [39], submandibular gland flap [15], fascia lata [42] and posterior belly of digastric flap [50]. However, these reports are not conclusive enough for their use. Further studies comparing these flaps with commonly used flaps are recommended.

The present meta-analysis was specifically conducted to evaluated the efficacy of SMMMF in the prevention of FS following parotidectomy. Results of this analysis state that SCMMF gives a promising result but there are numerous factors that could confound results. The most important factor is the heterogeneity among the studies having different clinical and methodologic parameters. Most of the studies included are observational studies, despite the fact that RCTs are considered to be the highest level of evidence in decision-making. Inclusion of retrospective studies with a long length of follow-up also increase the chances of recall bias [51]. Another aspect is that most of the studies did not make specific inclusion criteria resulting in improper selection of the patients and affecting the end result. This bias is known as “selection bias” which is one of the most important biases affecting the study [52]. Reporting bias is another bias which is associated with reporting of age, gender and other clinical characteristics of the patients [53].

Most studies in the analysis suffer from lack of power due to small sample size [54]. This may result in a false negative conclusion. Another variable is the surgical technique with which the SCMMF is elevated and used. There is no standard technique which has been used in the studies, neither there is any mention of the dimensions of the flap to be raised. Some authors used an inferiorly based flap, whereas others used a superiorly based flap. Kim and Mathog [12] used only the superficial layer of SCMMF along with the platysma muscle and cervical fascia.

Method of detection for gustatory sweating is another confounding factor. The gold standard method to detect the objective FS is the Minor’s iodine starch test, [13, 55] but there is no standard technique and quantification of results as true or false positives. Reporting the incidence of objective FS is sometimes influenced by the existence of subjective symptoms. Length of follow-up is another factor. It has been mentioned that there is a latency period of six months for FS to develop. Hence, a lesser follow-up would underestimate the occurrence of FS. Also, longer follow-up may result in less reporting of subjective symptoms as the patient may develop tolerance in such a long time. It is also not clear if the interposition of SCMMF actually inhibits the FS or just delays it. A smaller follow-up may misconclude that SCMMF decreases the incidence of FS. Hence, it is imperative to have enough follow-up period to distinguish between the inhibition and delay of FS.

Cosmetic results were measured only in a few studies with heterogeneous methods among the studies. However, they are found to be better in flap groups. Nofal et al. [56] in their study concluded that partial thickness superiorly based SCM flap is an effective cosmetic option for reconstruction following parotidectomy.

Conclusion

The analysis suggests that SCMMF reduces the incidence of FS but considering various confounding factors, it is difficult to arrive at a conclusion. However, it is beneficial to use this flap as it also improves the cosmetic deformity. Effectiveness of SCMMF in prevention of FS can be identified by a well-constructed multi-centre RCT with proper guidelines, adequate sample size, standardized setting and proper follow-up.

Funding

None.

Compliance with ethical standards

Conflict of interest

None.