Posterior Belly of Digastric Muscle Transposition Flap in Preventing Frey's Syndrome after Superficial Parotidectomy- A Prospective Study.

Introduction: Superficial parotidectomy is an effective management for benign and malignant tumours of the superficial lobe of the parotid gland. Frey's syndrome is one of the most common complications observed after parotidectomy. The objective of our study was to find the incidence of Frey's syndrome 6 months and 1 year postoperatively after doing posterior belly of the digastric flap during superficial parotidectomy. Materials and
Methods: This is an observational prospective study done in the Department of General Surgery of the Institute from November 2018 to December 2020. Thirty-eight patients with parotid swellings (both due to benign or malignant causes) were evaluated preoperatively and planned for superficial parotidectomy with a posterior belly of digastric muscle (PBDM) flap to prevent the occurrence of Frey's syndrome. They were followed up in 6 months and 1 year. Minor's test was done in each visit to look for the occurrence of Frey's syndrome.
Results: Two patients (5.2%) out of 38 patients developed asymptomatic Frey's syndrome after 6 months postoperatively out of which one patient (2.6%) developed symptomatic Frey's syndrome after 9 months postoperatively with symptoms such as sweating, flushing, and redness over the parotid area during chewing. Discussion: PBDM flap following superficial parotidectomy in a single-stage surgery is an effective and easy method to prevent Frey's syndrome. This procedure is easy to perform and requires no complex dissection. There have not been many studies regarding the use of this flap; hence, this study may be considered as a pilot study. Copyright:

INTRODUCTION

Superficial parotidectomy is an effective management for benign and malignant tumours of the superficial lobe of the parotid gland.[12] Gustatory sweating (Frey's syndrome) is a common complication after parotidectomy due to abnormal regeneration of the secretomotor parasympathetic fibers of auriculotemporal nerve, which aberrantly supply the skin over the parotid.[3] The injured nerve fibers regenerate and innervate the sweat glands of the skin overlying the parotid region, which cause sweating on chewing and thought of food. The parasympathetic innervation of the parotid gland arises in the brain stem at the superior salivatory nucleus and the fibers travel with the ninth cranial nerve and enter the middle ear as Jacobson's nerve, and then emerges from the roof of the petrous pyramid as the lesser petrosal nerve. After that, it passes through the foramen ovale to relay at the otic ganglion at the infratemporal fossa. The postganglionic fibers reach the parotid gland through the auriculotemporal nerve. After parotidectomy, these nerve fibers aberrantly regenerate and supply the sweat glands present in the skin over the parotid.[345] The incidence of Frey's syndrome after parotidectomy can be as high as 96% when the starch iodine test (Minor's test) is done according to the literature. Only a few patients become symptomatic for Frey's syndrome according to various studies after parotidectomy.[456] Many methods have been described using flaps and grafts to reduce the chances of Frey's syndrome after superficial parotidectomy such as fascia lata graft,[7] sternocleidomastoid flap,[8] dermal fat graft,[9] platysma muscle flap,[10] temporoparietal fascia flap,[11] and polytetrafluoroethylene implant.[12] The posterior belly of the digastric muscle (PBDM) flap is a novel, easy, and effective procedure to prevent Frey's syndrome in parotidectomy patients.[13]

MATERIALS AND METHODS

Patients

This observational prospective study was done in the general surgery department of our institute from November 2018 to December 2020. The study was approved by the institutional ethics committee vide IEC Appln. No:-252/26.08.2020. The study included all the patients who attended the surgery clinic of our institution with a parotid swelling involving only the superficial lobe due to any cause (benign lesion, malignancy) after obtaining a valid consent.

Patients below 18 years and above 60 years of age, patients with life-threatening comorbidities (American Society of Anaesthesiology Grade-3 or more),[14] patients who require excision of deep lobe of parotid, and patients not giving consent to take part in the study were excluded from the study.

Methods

All patients in the study underwent routine preoperative investigations, ultrasonography of parotid region, and fine-needle aspiration cytology of the swelling, preanaesthetic evaluation before surgery.

After obtaining informed and written consent and explaining all the complications of surgery, patients were planned for surgery. General anaesthesia was administered and superficial parotidectomy was done with Modified Blair's incision[15] after identifying and protecting the facial nerve from any inadvertent injury. The PBDM originates [Figure 1] from the mastoid process of the temporal lobe and is inserted as a common digastric tendon. The branches of the occipital artery supply the posterior belly of digastric. It lies in close vicinity of the parotid and is used as one of the landmarks to identify facial nerves. The posterior belly of digastric [Figure 2] is detached from the common digastric tendon and sutured to the tissue near the tragus to fill the void after excision of the superficial lobe of parotid, care was taken to preserve the blood supply to the muscle belly. After transposition of the flap, the wound was closed with a close suction drain in situ. All patients were given standard postoperative care after surgery. The drain was removed on postoperative day 2 and sutures were removed after 7 days and patients were followed up afterward in 6 months and 1 year.

Figure 1

Posterior belly of digastric muscle (black arrow) before being transposed on the parotid bed bearing branches of facial nerve (green arrow)

Figure 2

Posterior belly of digastric muscle after being transposed (black arrow)

In every visit, Minor's test[16] was done in the biochemistry department of the institute by a trained technician to look for the occurrence of Frey's syndrome. Sweating due to stress and anxiety might hamper the results, but its occurrence was unlikely.[16] A positive test with symptoms such as sweating, flushing, and redness over the parotid area during chewing is diagnosed as symptomatic Frey's syndrome and without symptom is diagnosed as asymptomatic Frey's syndrome.

Statistical analysis

Statistical analysis was done using Microsoft Excel version 2013 and the proportional incidence was calculated. Parametric numerical data were reported as mean ± standard deviation for continuous variables; nonparametric numerical data were represented as median (range). As this is not a comparative study, P value was not used in the results.

With the above criteria, 40 patients were selected. Two of the patients were lost to follow-up. Hence, 38 patients were included in the study. Among the patients, 23 (60.52%) males and 15 (39.48%) females undergone superficial parotidectomy during the study period and flap reconstruction using the PBDM was done in all. The demographic data and various outcomes of the study are depicted in Table 1. Five (13.15%) patients developed complications in the postoperative period (2 [5.2%] wound infection, 1 [2.6%] parotid fistula, and 2 [5.2%] Frey's syndrome). All complications were managed conservatively in the postoperative period. Two patients (5.2%) showed positive Minor's test after 6 months of surgery which means asymptomatic Frey's syndrome (patients with positive Minor's test but no symptoms of Frey's syndrome). Only one patient (2.6%) developed symptoms after 9 months of surgery who improved after local application of scopolamine over the affected area.

Table 1

Results

Variables	Results
Total cases (%)	38
Males	23 (60.52)
Females	15 (39.48)
Age (years), mean±SD (range)	48.3±8.75 (32-67)
BMI (kg/m2), mean±SD (range)	22.1±1.97 (18.7-26.6)
Diagnosis (%)
Pleomorphic adenoma	26 (68.42)
Warthin’s tumour	12 (31.58)
Operative time (min), mean±SD (range)	59.2±11 (48-92)
Length of hospital stay (days), mean±SD (range)	2.6±0.75 (2-5)
Postoperative complications (%)
Wound infection	2 (5.2)
Parotid fistula	1 (2.6)
Frey’s syndrome	2 (5.2)

SD: Standard deviation, BMI: Body mass index

DISCUSSION

Frey's syndrome is believed to be caused by an aberrant regeneration of the injured parasympathetic nerve fibers of the parotid gland during parotidectomy. The injured nerve fibers regenerate and innervate the sweat glands of the overlying skin of the parotid region which cause gustatory sweating. The parasympathetic innervation of the parotid gland originates in the brain stem at the superior salivatory nucleus. The fibers travel with the ninth cranial nerve and enter the middle ear as Jacobson's nerve, and then emerges from the roof of the petrous pyramid as the lesser petrosal nerve. After that, it passes through the foramen ovale to relay at the otic ganglion at the infratemporal fossa. The postganglionic fibers reach the parotid gland through the auriculotemporal nerve.[34] This can be prevented by placing a flap of tissue between the skin and the space created after parotidectomy.[10]

The incidence of asymptomatic Frey's syndrome after a posterior belly of the digastric flap after superficial parotidectomy is only 5.2%, in our study, while the incidence of symptomatic disease is only 2.6%. In contrast to doing parotidectomy without flap reconstruction of the defect which has an incidence rate for gustatory sweating of 94%,[45] the PBDM flap is a much better alternative. Casler and Conley used the sternocleidomastoid muscle flap and found out the incidence of symptomatic Frey's syndrome to be 12.5% in their study.[8] Kim and Mathog reported the incidence of Frey's syndrome (22.2%) in their study using platysma muscle flap.[10] Rapport and Allison used a platysma muscle flap and found the incidence of Frey's syndrome to be 4%.[17] Other flap techniques such as fascia lata graft, dermal fat flap, and platysma flap have a higher learning curve and are associated with complex dissection. The PBDM flap is technically very easy to perform with no complex dissection.[13]

CONCLUSION

The PBDM flap is technically very easy to perform and no complex dissection is required. There have not been many studies regarding the use of this flap; hence, this study may be considered as a pilot study. The limitations of the study are the small sample size, shorter follow-up period, and no comparison with the available other methods. In future to establish PBDM flap after superficial parotidectomy as a definitive option to prevent the occurrence of Frey's syndrome, more number of randomized control trials are required.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.