Eur Arch Otorhinolaryngol DOI 10.1007/s00405-015-3622-9
HEAD AND NECK
The effect of partial superficial parotidectomy on amplitude, latency and threshold of facial nerve stimulation Kerem Ozturk1, • Serdar Akyildiz1 • Sercan Gode1 • Goksel Turhal1 Gulce Gursan1 • Tayfun Kirazli1
•
Received: 3 March 2015 / Accepted: 3 April 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract The aim of this study is to assess the effect of partial superficial parotidectomy and facial nerve dissection to electrophysiologic parameters of intraoperative facial nerve monitoring such as nerve stimulation threshold, stimulus amplitude and latency. Twenty-five patients who underwent partial superficial parotidectomy for benign parotid gland mass were included in the study. After the identification of the facial nerve main trunk, minimum stimulation threshold, latencies and amplitudes of the orbicularis oculi (electrode 1) and orbicularis oris (electrode 2) electrodes at 0.50 milliamperes (mA) were recorded. All of the recordings were repeated after the completion of parotidectomy. Median nerve dissection duration was calculated and size of the tumors was measured during macroscopic pathology. The median minimum nerve stimulation threshold was 0.15 mA [interquartile range (IQR) = 0.05] before and 0.15 mA (IQR = 0.08) after the parotidectomy (p = 0.02). Median nerve dissection duration was 49 min (IQR = 38). Median amplitude and latency in electrode 1 before and after the facial nerve dissection were 322 millivolts (mV) (IQR = 330), 370 mV (IQR = 370) (p = 0.02), 3 milliseconds (ms) (IQR = 1) and 4 ms (IQR = 2) (p = 0.05), respectively. Median amplitude and latency in electrode 2 before and after the facial nerve dissection were 396 mV (IQR = 275), 365 mV (IQR = 836) (p = 0.86), 3 ms (IQR = 1.5) and 4 ms (IQR = 1.5) (p = 0.17), respectively. Minimal nerve stimulation threshold and amplitude of electrode 1 were affected by facial nerve dissection among the & Kerem Ozturk [email protected] 1
Department of Otolaryngology, Ege University School of Medicine, Bornova, Izmir, Turkey
electrophysiologic parameters (p = 0.02 and p = 0.02). Of the electrophysiological parameters only the latency of electrode 2 was significantly correlated with tumor size (p = 0.03). Besides, none of the parameters were predictive for a possible postoperative facial nerve dysfunction regarding superficial partial parotidectomy. Keywords Facial nerve Parotidectomy Electrophysiology
Introduction Salivary gland tumors constitute 3 % of the tumors in the head and neck region and 70–80 % of the salivary gland tumors are localized in the parotid gland [1]. Approximately 80 % percent of the parotid gland masses are benign with the most common histopathologic type being pleomorphic adenoma (60–70 %). Surgery is the mainstay of treatment in parotid gland tumors. Superficial and most of the time partial superficial parotidectomy is the choice of the treatment in tumors arising from the superficial part of the parotid gland [2, 3]. One of the most bothersome and disappointing complications of this surgery is temporary or permanent facial paralysis. Temporary facial nerve dysfunction can be as high as 40 % of the patients undergoing parotidectomy while permanent facial nerve paralysis is less common and accounting between 0 and 6 % [2, 4, 5]. Facial nerve dysfunction can be quite disfiguring and can cause significant cosmetic and functional morbidity, ocular complications and psychological effects [6]. Thus, maximal preservation of facial nerve anatomy and function is of great importance. Even though intraoperative electrophysiologic facial nerve monitoring is being more widely used to assist surgeons during parotidectomy to lower the risk of facial nerve injury,
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in depth knowledge of the surgical anatomy is indispensable. Continuous facial nerve monitoring was found helpful during parotidectomy [7]. Preoperative and postoperative intraoperative facial nerve stimulation thresholds did not show a correlation with facial nerve dysfunction related to parotidectomy in a previous study conducted by the authors of this study [8]. Similarly, Meier et al. [9] and Cillero Ruiz et al. [10] reported no correlation of intraoperative nerve responses with postoperative facial nerve function. However, Brennan et al. [7] reported that an elevated nerve response [[0.5 milliamperes (mA)] was predictive of postoperative facial paresis. The aim of this study is to assess the effect of partial superficial parotidectomy and facial nerve dissection to electrophysiologic parameters of intraoperative facial nerve stimulation and monitoring such as nerve stimulation threshold, stimulus amplitude and latency.
Materials and methods This study was carried out at Ege University Otolaryngology Department which is a part of a tertiary medical center between September 2013 and December 2014. It has been conducted in concordance with international ethical standards and World Health Organisation Helsinki Declaration. It was approved by Ege University Research Ethical Committee. Informed consent was obtained from all of the subjects. The study was designed as a prospective observational study. All of the data were prospectively collected. These included patient name, social security number, age, sex, medical history, date of the surgery, electrophysiologic recording, preoperative and postoperative facial nerve function. Patient selection Twenty-five patients who underwent partial superficial parotidectomy due to benign parotid gland mass were included in the study. Thirteen (52 %) of the patients were female and twelve (48 %) were male. Patients who required total parotidectomy had a malignant histopathology or a known peripheral nerve dysfunction were excluded. Patients with a history of prior parotid gland surgery were also excluded. Thirty patients were operated due to parotid gland mass during the mentioned time interval and five patients were excluded due to malignant final pathology. Instrumentation Monitoring was performed by the commercially available electrophysiologic nerve monitoring system NIM-
123
Response 3.0 Nerve Integrity Monitor (NIM-Response 3.0; Medtronic Xomed, Jacksonville, FL). Procedure All of the tumors showed benign fine-needle aspiration cytology and benign physical appearance on magnetic resonance imaging (MRI). All of the patients were operated under endotracheal general anesthesia. Only short acting muscle relaxants were used during the induction of anesthesia and they were discontinued throughout the operation. Two needle electrodes were placed. One was placed to the orbicularis oculi muscle (electrode 1). The other electrode was placed to the orbicularis oris muscle (electrode 2). Ground and stimulator anode electrodes were placed, too. Also a stimulation probe was included in the sterile operating field. All of the parotidectomies were performed by three different staff surgeons experienced in the field of head and neck surgery. After the initial incisions were made, attention was given to identify the main trunk of the facial nerve where it initially entered the parotid gland. After the main truck was found, the nerve was dissected completely from surrounding the tissue at the level of initial identification. Then the nerve was stimulated with 0.50 mA. The amplitude and the latency were recorded. After that, the stimulation level was lowered to 0.05 mA. The minimum achievable stimulation level was found with 0.05 mA increases and this was recorded as the minimum stimulation threshold. Facial nerve dissection and partial superficial parotidectomy was completed after these recordings. The duration of the facial nerve dissection was also recorded beginning from the initial identification of the main trunk to the end of the nerve dissection. All of the previous recordings were repeated after the completion of parotidectomy. Special care was given to stimulate at the same exact point of the previous stimulation on the main trunk. Facial nerve function of the patients were evaluated with the House–Brackmann facial nerve grading system preoperatively and assessed for early clinical postoperative facial nerve function in the postoperative 24-h period [11]. Outcome measures Multiple parameters were evaluated to assess the effects of partial superficial parotidectomy on facial nerve electrophysiology. Amplitude, threshold and latency were compared before and after the competition of superficial parotidectomy. Facial nerve functions were measured according to the House–Brackmann facial nerve grading system both preoperatively and postoperatively. Size of the tumor was measured during macroscopic pathology.
Eur Arch Otorhinolaryngol
Statistical analysis Statistical analysis was made using computer software (SPSS version 22.0, SPSS Inc. Chicago, IL, USA). Chisquare (v2) exact tests were used for the comparison of categorical data. Independent and paired sample t tests were used for the analysis of parametric variables while Wilcoxon and Mann–Whitney U tests were used for the analysis of non-parametric variables based on the distribution pattern of the data. The Shapiro–Wilk test was used for determining the distribution pattern of the data. The distribution of the groups was non-parametric. Correlation analysis was performed via Pearson or Spearman correlation analysis based on the distribution pattern of the data. Data were expressed as ‘‘median, interquartile range (IQR)’’. A p value less than 0.05 was considered as statistically significant.
Results The median age of 25 patients included in the study was 49 (IQR = 23.5, 14–73) years. The postoperative histopathological analysis revealed that 13 (52 %) of the patients were diagnosed as pleomorphic adenoma and 12 (48 %) as Warthin’s tumor. The tumors were measured in length according to their largest dimension. Median tumor size was found 2.3 cm (IQR = 1.2) with the smallest measuring 0.80 cm and the largest 3.80 cm. Four (16 %) of the patients had postoperative facial paresis which was resolved spontaneously in the following postoperative first week with no specific treatment. Formerly mentioned 4 patients had grade 2 facial paralysis and the paralysis was in the cervicofacial branch. The median minimum nerve stimulation threshold was 0.15 mA (IQR = 0.05 mA) before the parotidectomy and 0.15 mA (IQR = 0.08 mA) after the parotidectomy
(p = 0.02). Median nerve dissection duration was 49 min (IQR = 38). Median amplitude and latency in electrode 1 before and after the facial nerve dissection were 322 millivolts (mV) (IQR = 330 mV), 370 mV (IQR = 370 mV), 3 milliseconds (ms) (IQR = 1 ms) and 4 ms (IQR = 2 ms), respectively (Table 1). Median amplitude and latency in electrode 2 before and after the facial nerve dissection were 396 mV (IQR = 275 mV), 365 mV (IQR = 836 mV), 3 ms (IQR = 1.5 ms) and 4 ms (IQR = 1.5 ms), respectively (Table 1). Partial superficial parotidectomy did not cause a statistically significant difference in electrode 1 and 2 latencies (p = 0.05 and p = 0.17). Also no statistically significant difference was found between the preoperative and postoperative amplitudes in electrode 2 (p = 0.86). However, there was a significant difference between the amplitudes in electrode 1 (p = 0.02). There was a statistically significant difference between the minimum nerve stimulation thresholds before and after the parotidectomy (p = 0.02). Partial superficial parotidectomy and facial nerve dissection significantly elevated minimum nerve stimulation thresholds. However, there was no statistically significant difference between the House–Brackmann grade 1 and 2 patients regarding minimal stimulation thresholds, amplitudes and latencies of electrode 1 and 2 (p values were 0.94, 0.22, 0.76, 0.94 and 0.65, respectively). All of the electrophysiologic measurements were analyzed with receiver operating characteristic (ROC) and linear regression analysis and none of the electrophysiologic parameters were found to have a predictive value for postoperative facial paralysis. Tumor size did not cause a statistically significant difference in minimum stimulation threshold, amplitudes of electrode 1 and 2, and latency of electrode 1. The p values are given in Table 2. However, tumor size was significantly correlated with the latency of electrode 2
Table 1 Minimum nerve stimulation threshold, amplitude and latency medians Initial facial nerve trunk exposure
After facial nerve dissection
p value
Minimum nerve stimulation threshold (mA)
0.15 (IQR = 0.05)
0.15 (IQR = 0.08)
0.02
Electrode 1 amplitude (mV)
322 (IQR = 330)
370 (IQR = 560)
0.02
Electrode 2 amplitude (mV)
396 (IQR = 275)
365 (IQR = 836)
0.86
Electrode 1 latency (ms)
3 (IQR = 1)
4 (IQR = 2)
0.05
Electrode 2 latency (ms)
3 (IQR = 1.5)
4 (IQR = 1.5)
0.17
Table 2 Median tumor size and median facial nerve dissection duration and their relation with electrophysiologic parameters Median (IQR)
Minimum stimulation threshold, p value
Amplitudes for electrode 1 and 2, p value
Latencies for electrode 1 and 2, p value
Tumor size (cm)
2.3 (IQR = 1.3)
0.79
0.85, 0.36
0.47, 0.03
Duration of facial nerve dissection (min)
49 (IQR = 38)
0.79
0.74, 0.92
0.66, 0.49
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(p = 0.03). No statistically significant difference was found between age of the patients and minimum stimulation threshold, amplitudes and latencies of electrode 1 and 2 (Table 2). The duration of facial nerve dissection did not cause a statistically significant difference in the minimum stimulation threshold, amplitudes and latencies of electrode 1 and 2 (Table 2). Also duration of the facial nerve dissection did not significantly predict postoperative facial paralysis (p = 0.63).
Discussion Injury to the facial nerve is one of the most undesirable complications of superficial parotidectomy. Injury to the nerve during superficial parotidectomy can be caused by many mechanisms. These are transection, laceration, clamp compression, retraction, electrocautery injury, ligature entrapment, suction trauma and ischemia [12]. Electrophysiologic monitoring and electrical stimulation of the facial nerve can assist the surgeon especially in cases where the identification of the facial nerve is difficult in despite of the use of anatomic landmarks [13]. These conditions may include anatomic distortion caused by the mass effect of a large tumor or scarring due to previous surgery. Besides differentiating facial nerve from sensory nerves or other soft tissue, electrophysiologic nerve monitoring may be used to assess nerve integrity and predict postoperative facial nerve function. Facial nerve monitoring was also found successful in locating and identifying the facial nerve [14]. Many reports exist in the literature regarding intraoperative facial nerve monitoring during neurologic surgery and parotidectomy. In a study including 109 patients who underwent excision for acoustic neuroma, it was found that higher stimulus thresholds were related to a statistically significant poor initial facial nerve outcome and also a more common long-term impaired facial nerve function [15]. Cillero Ruiz et al. [10] reported their experience with 35 patients and they found no correlation between the recorded intraoperative response and the early postoperative functional results. Also the results of 45 patients who underwent parotidectomy in a study conducted by Meier et al. [9] suggest that abnormalities in the facial nerve monitor during parotidectomy did not predict facial nerve injury. Similarly Grosheva et al. [16] reported that electromyographic facial nerve monitoring during parotidectomy for benign lesions did not diminish either the incidence of postoperative facial paralysis or the final facial outcome. Ceyhan et al. [17] reported electrophysiologic findings of 31 patients undergoing otologic, neurologic and parotid
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gland surgeries. Authors of this study found elevated nerve stimulation thresholds (0.60 ± 0.83 vs. 0.23 ± 0.13 mA) in patients with postoperative facial nerve paralysis. All except one of the nonparalytic nerves could be stimulated with a stimulus level lower than 0.30 mA. There was facial nerve dysfunction in four of the patients despite having a threshold lower than 0.30 mA. They found that stimulation threshold was insufficient in predicting postoperative facial nerve function. Brennan et al. [7] reported their intraoperative electromyographic monitoring results with 44 parotidectomy and 70 thyroidectomy/parathyroidectomy patients. They found that the minimal nerve stimulation level was not predictive of isolated nerve branch weakness with a stimulation range of 0.2 and 0.5 mA which was identical to patients with normal postoperative facial function. However, one patient with total postoperative paralysis (grade VI) had a minimal nerve stimulation threshold of 1.0 mA. Therefore, they suggested that minimum stimulation level exceeding 0.5 mA at the end of parotidectomy may predict postoperative complete facial nerve paralysis. Neff et al. [18] evaluated facial nerve monitoring parameters as a predictor of postoperative facial nerve outcomes of 74 patients undergoing vestibular schwannoma. They found that minimal stimulus intensity of 0.05 mA or less and response amplitude of 240 mV or greater was predictive of a House–Brackmann grade I or II outcome with a 98 % probability. Mamelle et al. [19] used supramaximal stimulation at 2 mA and they reported that postdissection to predissection ratios of maximal response amplitude was indicative of a nerve conduction block and found significantly lower in the patient group with a poor outcome compared with the group with a normal facial function. Even though a statistically significant difference was found regarding minimum stimulation threshold in our cohort of 25 patients, this did not predict the outcome of facial nerve paralysis seen in four of the patients. Also partial superficial parotidectomy did not cause a statistically significant difference in the electrophysiologic parameters regarding amplitude and latency other than amplitude recordings of electrode 1. The statistically significant increase in the amplitudes of electrode 1 had no clinical implication because none of the patients had any degree of facial nerve dysfunction in the zygomaticofacial branch. All of the patients with postoperative facial nerve dysfunction only had mild (grade 2) facial nerve paresis. According to our study it is not possible to conclude how electrophysiologic parameters would predict the degree of facial nerve dysfunction. All of the electrophysiologic measurements were analyzed with receiver operating characteristic (ROC) and linear regression analysis and none of the electrophysiologic parameters were found to have a predictive value for postoperative facial paralysis.
Eur Arch Otorhinolaryngol
Increased tumor size is most of the time associated with distorted anatomy and displaced facial nerve making the surgery more challenging. Of the electrophysiological parameters only the latency of buccal and marginal mandibular branches of the facial nerve was significantly correlated with tumor size (p = 0.03). However, tumor size was not a predictive factor of postoperative facial nerve function. The length of facial nerve dissection is not the same in every case. The extent of the partial superficial parotidectomy differs with respect to individual factors such as location, size of the tumor and variances in anatomy. The length of dissection is different in each patient and this is extremely hard to measure. This is a shortcoming of the study limiting the reliability of electrophysiologic measurements in electrodes 1 and 2. Also the cervicofacial branch most of the time requires longer dissection compared to the zygomaticofacial branch. This is also a shortcoming of the study limiting the comparison of the electrophysiologic measurements of electrodes 1 and 2. After the identification of the main trunk, the soft tissue was dissected off the nerve. However, there is a possibility of a residual layer of soft tissue or a fascial layer interfering with nerve stimulation and electrophysiologic recording. This could be the reason of the higher amplitudes recorded in some of the patients following nerve dissection.
Conclusion This study revealed that only the minimal nerve stimulation threshold and amplitude of the orbicularis oculi electrode were affected by facial nerve dissection among the electrophysiologic parameters. Larger tumor size yielded a significantly higher latency on orbicularis oris electrode. However, none of the parameters were predictive for a possible postoperative facial nerve dysfunction. Intraoperative facial nerve monitoring has no benefit in the prediction of postoperative facial nerve function. Conflict of interest
None.
References 1. Lin C-C, Tsai M-H, Huang C-C, Hua C-H, Tseng H-C, Huang S-T (2008) Parotid tumors: 10-year experience. Am J Otolaryngol Head Neck Med Surg 29:94–100 2. Guintinas-Lichius O, Klussmann JP, Wittekindt C, Stennert E (2006) Parotidectomy for benign parotid disease at a university teaching hospital: outcome of 963 operations. Laryngoscope 116:534–540 3. Roh JL, Kim HS, Park CI (2007) Randomized clinical trial comparing partial parotidectomy versus superficial or total parotidectomy. Br J Surg 94(9):1081–1087
4. Nouraei SA, Ismail Y, Ferguson MS, McLean NR, Milner RH, Thomson PJ, Welch AR (2008) Analysis of complications following surgical treatment of benign parotid disease. ANZ J Surg 78(3):134–138 5. Witt RL (1999) Facial nerve function after partial superficial parotidectomy: an 11-year review (1987–1997). Otolaryngol Head Neck Surg 121(3):210–213 6. Ryzenman JM, Pensak ML, Tew Jm Jr (2005) Facial paralysis and surgical rehabilitation: a quality of life analysis in a cohort of 1595 patients after acoustic neuroma surgery. Otol Neurotol 26:516–521 7. Brennan J, Moore E, Shuler KJ (2001) Prospective analysis of the efficacy of continuous intraoperative nerve monitoring during thyroidectomy, parathyroidectomy, and parotidectomy. Otolaryngol Head Neck Surg 124:537–543 8. Ozturk K, Gode S, Gursan G, Kirazli T (2015) Is it possible to predict postoperative facial nerve function by monitorization during parotidectomy. Kulak Burun Bogaz Ihtis Derg 25:1–4 (in press) 9. Meier JD, Wenig BL, Manders EC, Nenonene EK (2006) Continuous intraoperative facial nerve monitoring in predicting postoperative injury during parotidectomy. Laryngoscope 116:1569–1572 10. Cillero Ruiz G, Espinosa Sanchez JM, de Ruis Erechun Lasa I et al (1994) Intraoperative facial nerve monitoring: results. Acta Otorrinolaringol Esp 45:425–431 11. House JW, Brackmann DW (1985) Facial nerve grading system. Otolaryngol Head Neck Surg 93:146–147 12. Gillespie MB, Eisele DW (2009) Complications of surgery of the salivary glands. In: Eisele DW, Smith RV (eds) Complications in head and neck surgery, 2nd edn. Mosby Elsevier, Philadelphia, pp 221–39 13. Eisele DW, Wang SJ, Orloff LA (2010) Electrophysiologic facial nerve monitoring during parotidectomy. Head Neck 32(3):399–405 14. Doikov IY, Konsulov SS, Dimov RS (2001) Stimulation electromyography as a method of intraoperative localization and identification of the facial nerve during parotidectomy: review of 15 consecutive parotid surgeries. Folia Med (Plovdiv) 43:23–26 15. Zeituni AG, Hammerschlag PE, Cohen NL (1997) Prognostic significance of intraoperative stimulus thresholds. Am J Otol 18(4):494–497 16. Grosheva M, Klussmann JP, Grimminger C, Wittekindt C, Beutner D, Pantel M, Volk GF, Guntinas-Lichius O (2009) Electromyographic facial nerve monitoring during parotidectomy for benign lesion does not improve the outcome of postoperative facial nerve function: a prspective two-center trial. Laryngoscope 119(12):2299–2305 17. Ceyhan A, Satar B, Yetiser S, Hidir Y, Durmaz A, Gerek M (2011) Stimulation thresholds and response parameters of the facial nerve as prognostic factors in facial nerve exploration. KBB ve BBC Dergisi 19(3):150–155 18. Neff BA, Ting J, Dickinson SL, Welling DB (2005) Facial nerve monitoring parameters as a predictor of postoperative facial nerve outcomes after vestibular schwannoma resection. Otol Neurotol 26(4):728–732 19. Mamelle E, Bernat I, Pichon S, Granger B, Sain-Oulhen C, Lamas G, Tankere F (2013) Supramaximal stimulation during intraoperative facial nerve monitoring as a simple parameter to predict early functional outcome after parotidectomy. Acta Otolaryngol 133(7):779–784
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HEAD AND NECK
The effect of partial superficial parotidectomy on amplitude, latency and threshold of facial nerve stimulation Kerem Ozturk1, • Serdar Akyildiz1 • Sercan Gode1 • Goksel Turhal1 Gulce Gursan1 • Tayfun Kirazli1
•
Received: 3 March 2015 / Accepted: 3 April 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract The aim of this study is to assess the effect of partial superficial parotidectomy and facial nerve dissection to electrophysiologic parameters of intraoperative facial nerve monitoring such as nerve stimulation threshold, stimulus amplitude and latency. Twenty-five patients who underwent partial superficial parotidectomy for benign parotid gland mass were included in the study. After the identification of the facial nerve main trunk, minimum stimulation threshold, latencies and amplitudes of the orbicularis oculi (electrode 1) and orbicularis oris (electrode 2) electrodes at 0.50 milliamperes (mA) were recorded. All of the recordings were repeated after the completion of parotidectomy. Median nerve dissection duration was calculated and size of the tumors was measured during macroscopic pathology. The median minimum nerve stimulation threshold was 0.15 mA [interquartile range (IQR) = 0.05] before and 0.15 mA (IQR = 0.08) after the parotidectomy (p = 0.02). Median nerve dissection duration was 49 min (IQR = 38). Median amplitude and latency in electrode 1 before and after the facial nerve dissection were 322 millivolts (mV) (IQR = 330), 370 mV (IQR = 370) (p = 0.02), 3 milliseconds (ms) (IQR = 1) and 4 ms (IQR = 2) (p = 0.05), respectively. Median amplitude and latency in electrode 2 before and after the facial nerve dissection were 396 mV (IQR = 275), 365 mV (IQR = 836) (p = 0.86), 3 ms (IQR = 1.5) and 4 ms (IQR = 1.5) (p = 0.17), respectively. Minimal nerve stimulation threshold and amplitude of electrode 1 were affected by facial nerve dissection among the & Kerem Ozturk [email protected] 1
Department of Otolaryngology, Ege University School of Medicine, Bornova, Izmir, Turkey
electrophysiologic parameters (p = 0.02 and p = 0.02). Of the electrophysiological parameters only the latency of electrode 2 was significantly correlated with tumor size (p = 0.03). Besides, none of the parameters were predictive for a possible postoperative facial nerve dysfunction regarding superficial partial parotidectomy. Keywords Facial nerve Parotidectomy Electrophysiology
Introduction Salivary gland tumors constitute 3 % of the tumors in the head and neck region and 70–80 % of the salivary gland tumors are localized in the parotid gland [1]. Approximately 80 % percent of the parotid gland masses are benign with the most common histopathologic type being pleomorphic adenoma (60–70 %). Surgery is the mainstay of treatment in parotid gland tumors. Superficial and most of the time partial superficial parotidectomy is the choice of the treatment in tumors arising from the superficial part of the parotid gland [2, 3]. One of the most bothersome and disappointing complications of this surgery is temporary or permanent facial paralysis. Temporary facial nerve dysfunction can be as high as 40 % of the patients undergoing parotidectomy while permanent facial nerve paralysis is less common and accounting between 0 and 6 % [2, 4, 5]. Facial nerve dysfunction can be quite disfiguring and can cause significant cosmetic and functional morbidity, ocular complications and psychological effects [6]. Thus, maximal preservation of facial nerve anatomy and function is of great importance. Even though intraoperative electrophysiologic facial nerve monitoring is being more widely used to assist surgeons during parotidectomy to lower the risk of facial nerve injury,
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in depth knowledge of the surgical anatomy is indispensable. Continuous facial nerve monitoring was found helpful during parotidectomy [7]. Preoperative and postoperative intraoperative facial nerve stimulation thresholds did not show a correlation with facial nerve dysfunction related to parotidectomy in a previous study conducted by the authors of this study [8]. Similarly, Meier et al. [9] and Cillero Ruiz et al. [10] reported no correlation of intraoperative nerve responses with postoperative facial nerve function. However, Brennan et al. [7] reported that an elevated nerve response [[0.5 milliamperes (mA)] was predictive of postoperative facial paresis. The aim of this study is to assess the effect of partial superficial parotidectomy and facial nerve dissection to electrophysiologic parameters of intraoperative facial nerve stimulation and monitoring such as nerve stimulation threshold, stimulus amplitude and latency.
Materials and methods This study was carried out at Ege University Otolaryngology Department which is a part of a tertiary medical center between September 2013 and December 2014. It has been conducted in concordance with international ethical standards and World Health Organisation Helsinki Declaration. It was approved by Ege University Research Ethical Committee. Informed consent was obtained from all of the subjects. The study was designed as a prospective observational study. All of the data were prospectively collected. These included patient name, social security number, age, sex, medical history, date of the surgery, electrophysiologic recording, preoperative and postoperative facial nerve function. Patient selection Twenty-five patients who underwent partial superficial parotidectomy due to benign parotid gland mass were included in the study. Thirteen (52 %) of the patients were female and twelve (48 %) were male. Patients who required total parotidectomy had a malignant histopathology or a known peripheral nerve dysfunction were excluded. Patients with a history of prior parotid gland surgery were also excluded. Thirty patients were operated due to parotid gland mass during the mentioned time interval and five patients were excluded due to malignant final pathology. Instrumentation Monitoring was performed by the commercially available electrophysiologic nerve monitoring system NIM-
123
Response 3.0 Nerve Integrity Monitor (NIM-Response 3.0; Medtronic Xomed, Jacksonville, FL). Procedure All of the tumors showed benign fine-needle aspiration cytology and benign physical appearance on magnetic resonance imaging (MRI). All of the patients were operated under endotracheal general anesthesia. Only short acting muscle relaxants were used during the induction of anesthesia and they were discontinued throughout the operation. Two needle electrodes were placed. One was placed to the orbicularis oculi muscle (electrode 1). The other electrode was placed to the orbicularis oris muscle (electrode 2). Ground and stimulator anode electrodes were placed, too. Also a stimulation probe was included in the sterile operating field. All of the parotidectomies were performed by three different staff surgeons experienced in the field of head and neck surgery. After the initial incisions were made, attention was given to identify the main trunk of the facial nerve where it initially entered the parotid gland. After the main truck was found, the nerve was dissected completely from surrounding the tissue at the level of initial identification. Then the nerve was stimulated with 0.50 mA. The amplitude and the latency were recorded. After that, the stimulation level was lowered to 0.05 mA. The minimum achievable stimulation level was found with 0.05 mA increases and this was recorded as the minimum stimulation threshold. Facial nerve dissection and partial superficial parotidectomy was completed after these recordings. The duration of the facial nerve dissection was also recorded beginning from the initial identification of the main trunk to the end of the nerve dissection. All of the previous recordings were repeated after the completion of parotidectomy. Special care was given to stimulate at the same exact point of the previous stimulation on the main trunk. Facial nerve function of the patients were evaluated with the House–Brackmann facial nerve grading system preoperatively and assessed for early clinical postoperative facial nerve function in the postoperative 24-h period [11]. Outcome measures Multiple parameters were evaluated to assess the effects of partial superficial parotidectomy on facial nerve electrophysiology. Amplitude, threshold and latency were compared before and after the competition of superficial parotidectomy. Facial nerve functions were measured according to the House–Brackmann facial nerve grading system both preoperatively and postoperatively. Size of the tumor was measured during macroscopic pathology.
Eur Arch Otorhinolaryngol
Statistical analysis Statistical analysis was made using computer software (SPSS version 22.0, SPSS Inc. Chicago, IL, USA). Chisquare (v2) exact tests were used for the comparison of categorical data. Independent and paired sample t tests were used for the analysis of parametric variables while Wilcoxon and Mann–Whitney U tests were used for the analysis of non-parametric variables based on the distribution pattern of the data. The Shapiro–Wilk test was used for determining the distribution pattern of the data. The distribution of the groups was non-parametric. Correlation analysis was performed via Pearson or Spearman correlation analysis based on the distribution pattern of the data. Data were expressed as ‘‘median, interquartile range (IQR)’’. A p value less than 0.05 was considered as statistically significant.
Results The median age of 25 patients included in the study was 49 (IQR = 23.5, 14–73) years. The postoperative histopathological analysis revealed that 13 (52 %) of the patients were diagnosed as pleomorphic adenoma and 12 (48 %) as Warthin’s tumor. The tumors were measured in length according to their largest dimension. Median tumor size was found 2.3 cm (IQR = 1.2) with the smallest measuring 0.80 cm and the largest 3.80 cm. Four (16 %) of the patients had postoperative facial paresis which was resolved spontaneously in the following postoperative first week with no specific treatment. Formerly mentioned 4 patients had grade 2 facial paralysis and the paralysis was in the cervicofacial branch. The median minimum nerve stimulation threshold was 0.15 mA (IQR = 0.05 mA) before the parotidectomy and 0.15 mA (IQR = 0.08 mA) after the parotidectomy
(p = 0.02). Median nerve dissection duration was 49 min (IQR = 38). Median amplitude and latency in electrode 1 before and after the facial nerve dissection were 322 millivolts (mV) (IQR = 330 mV), 370 mV (IQR = 370 mV), 3 milliseconds (ms) (IQR = 1 ms) and 4 ms (IQR = 2 ms), respectively (Table 1). Median amplitude and latency in electrode 2 before and after the facial nerve dissection were 396 mV (IQR = 275 mV), 365 mV (IQR = 836 mV), 3 ms (IQR = 1.5 ms) and 4 ms (IQR = 1.5 ms), respectively (Table 1). Partial superficial parotidectomy did not cause a statistically significant difference in electrode 1 and 2 latencies (p = 0.05 and p = 0.17). Also no statistically significant difference was found between the preoperative and postoperative amplitudes in electrode 2 (p = 0.86). However, there was a significant difference between the amplitudes in electrode 1 (p = 0.02). There was a statistically significant difference between the minimum nerve stimulation thresholds before and after the parotidectomy (p = 0.02). Partial superficial parotidectomy and facial nerve dissection significantly elevated minimum nerve stimulation thresholds. However, there was no statistically significant difference between the House–Brackmann grade 1 and 2 patients regarding minimal stimulation thresholds, amplitudes and latencies of electrode 1 and 2 (p values were 0.94, 0.22, 0.76, 0.94 and 0.65, respectively). All of the electrophysiologic measurements were analyzed with receiver operating characteristic (ROC) and linear regression analysis and none of the electrophysiologic parameters were found to have a predictive value for postoperative facial paralysis. Tumor size did not cause a statistically significant difference in minimum stimulation threshold, amplitudes of electrode 1 and 2, and latency of electrode 1. The p values are given in Table 2. However, tumor size was significantly correlated with the latency of electrode 2
Table 1 Minimum nerve stimulation threshold, amplitude and latency medians Initial facial nerve trunk exposure
After facial nerve dissection
p value
Minimum nerve stimulation threshold (mA)
0.15 (IQR = 0.05)
0.15 (IQR = 0.08)
0.02
Electrode 1 amplitude (mV)
322 (IQR = 330)
370 (IQR = 560)
0.02
Electrode 2 amplitude (mV)
396 (IQR = 275)
365 (IQR = 836)
0.86
Electrode 1 latency (ms)
3 (IQR = 1)
4 (IQR = 2)
0.05
Electrode 2 latency (ms)
3 (IQR = 1.5)
4 (IQR = 1.5)
0.17
Table 2 Median tumor size and median facial nerve dissection duration and their relation with electrophysiologic parameters Median (IQR)
Minimum stimulation threshold, p value
Amplitudes for electrode 1 and 2, p value
Latencies for electrode 1 and 2, p value
Tumor size (cm)
2.3 (IQR = 1.3)
0.79
0.85, 0.36
0.47, 0.03
Duration of facial nerve dissection (min)
49 (IQR = 38)
0.79
0.74, 0.92
0.66, 0.49
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(p = 0.03). No statistically significant difference was found between age of the patients and minimum stimulation threshold, amplitudes and latencies of electrode 1 and 2 (Table 2). The duration of facial nerve dissection did not cause a statistically significant difference in the minimum stimulation threshold, amplitudes and latencies of electrode 1 and 2 (Table 2). Also duration of the facial nerve dissection did not significantly predict postoperative facial paralysis (p = 0.63).
Discussion Injury to the facial nerve is one of the most undesirable complications of superficial parotidectomy. Injury to the nerve during superficial parotidectomy can be caused by many mechanisms. These are transection, laceration, clamp compression, retraction, electrocautery injury, ligature entrapment, suction trauma and ischemia [12]. Electrophysiologic monitoring and electrical stimulation of the facial nerve can assist the surgeon especially in cases where the identification of the facial nerve is difficult in despite of the use of anatomic landmarks [13]. These conditions may include anatomic distortion caused by the mass effect of a large tumor or scarring due to previous surgery. Besides differentiating facial nerve from sensory nerves or other soft tissue, electrophysiologic nerve monitoring may be used to assess nerve integrity and predict postoperative facial nerve function. Facial nerve monitoring was also found successful in locating and identifying the facial nerve [14]. Many reports exist in the literature regarding intraoperative facial nerve monitoring during neurologic surgery and parotidectomy. In a study including 109 patients who underwent excision for acoustic neuroma, it was found that higher stimulus thresholds were related to a statistically significant poor initial facial nerve outcome and also a more common long-term impaired facial nerve function [15]. Cillero Ruiz et al. [10] reported their experience with 35 patients and they found no correlation between the recorded intraoperative response and the early postoperative functional results. Also the results of 45 patients who underwent parotidectomy in a study conducted by Meier et al. [9] suggest that abnormalities in the facial nerve monitor during parotidectomy did not predict facial nerve injury. Similarly Grosheva et al. [16] reported that electromyographic facial nerve monitoring during parotidectomy for benign lesions did not diminish either the incidence of postoperative facial paralysis or the final facial outcome. Ceyhan et al. [17] reported electrophysiologic findings of 31 patients undergoing otologic, neurologic and parotid
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gland surgeries. Authors of this study found elevated nerve stimulation thresholds (0.60 ± 0.83 vs. 0.23 ± 0.13 mA) in patients with postoperative facial nerve paralysis. All except one of the nonparalytic nerves could be stimulated with a stimulus level lower than 0.30 mA. There was facial nerve dysfunction in four of the patients despite having a threshold lower than 0.30 mA. They found that stimulation threshold was insufficient in predicting postoperative facial nerve function. Brennan et al. [7] reported their intraoperative electromyographic monitoring results with 44 parotidectomy and 70 thyroidectomy/parathyroidectomy patients. They found that the minimal nerve stimulation level was not predictive of isolated nerve branch weakness with a stimulation range of 0.2 and 0.5 mA which was identical to patients with normal postoperative facial function. However, one patient with total postoperative paralysis (grade VI) had a minimal nerve stimulation threshold of 1.0 mA. Therefore, they suggested that minimum stimulation level exceeding 0.5 mA at the end of parotidectomy may predict postoperative complete facial nerve paralysis. Neff et al. [18] evaluated facial nerve monitoring parameters as a predictor of postoperative facial nerve outcomes of 74 patients undergoing vestibular schwannoma. They found that minimal stimulus intensity of 0.05 mA or less and response amplitude of 240 mV or greater was predictive of a House–Brackmann grade I or II outcome with a 98 % probability. Mamelle et al. [19] used supramaximal stimulation at 2 mA and they reported that postdissection to predissection ratios of maximal response amplitude was indicative of a nerve conduction block and found significantly lower in the patient group with a poor outcome compared with the group with a normal facial function. Even though a statistically significant difference was found regarding minimum stimulation threshold in our cohort of 25 patients, this did not predict the outcome of facial nerve paralysis seen in four of the patients. Also partial superficial parotidectomy did not cause a statistically significant difference in the electrophysiologic parameters regarding amplitude and latency other than amplitude recordings of electrode 1. The statistically significant increase in the amplitudes of electrode 1 had no clinical implication because none of the patients had any degree of facial nerve dysfunction in the zygomaticofacial branch. All of the patients with postoperative facial nerve dysfunction only had mild (grade 2) facial nerve paresis. According to our study it is not possible to conclude how electrophysiologic parameters would predict the degree of facial nerve dysfunction. All of the electrophysiologic measurements were analyzed with receiver operating characteristic (ROC) and linear regression analysis and none of the electrophysiologic parameters were found to have a predictive value for postoperative facial paralysis.
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Increased tumor size is most of the time associated with distorted anatomy and displaced facial nerve making the surgery more challenging. Of the electrophysiological parameters only the latency of buccal and marginal mandibular branches of the facial nerve was significantly correlated with tumor size (p = 0.03). However, tumor size was not a predictive factor of postoperative facial nerve function. The length of facial nerve dissection is not the same in every case. The extent of the partial superficial parotidectomy differs with respect to individual factors such as location, size of the tumor and variances in anatomy. The length of dissection is different in each patient and this is extremely hard to measure. This is a shortcoming of the study limiting the reliability of electrophysiologic measurements in electrodes 1 and 2. Also the cervicofacial branch most of the time requires longer dissection compared to the zygomaticofacial branch. This is also a shortcoming of the study limiting the comparison of the electrophysiologic measurements of electrodes 1 and 2. After the identification of the main trunk, the soft tissue was dissected off the nerve. However, there is a possibility of a residual layer of soft tissue or a fascial layer interfering with nerve stimulation and electrophysiologic recording. This could be the reason of the higher amplitudes recorded in some of the patients following nerve dissection.
Conclusion This study revealed that only the minimal nerve stimulation threshold and amplitude of the orbicularis oculi electrode were affected by facial nerve dissection among the electrophysiologic parameters. Larger tumor size yielded a significantly higher latency on orbicularis oris electrode. However, none of the parameters were predictive for a possible postoperative facial nerve dysfunction. Intraoperative facial nerve monitoring has no benefit in the prediction of postoperative facial nerve function. Conflict of interest
None.
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