SONOGRAPHIC CHARACTERISTICS OF THE FACIAL NERVE IN HEALTHY VOLUNTEERS EMAN A. TAWFIK, MD Department of Physical Medicine & Rehabilitation, Faculty of Medicine, Ain Shams University, Cairo, Egypt. Accepted 24 February 2015 ABSTRACT: Introduction: Peripheral nerve ultrasound has become an effective imaging technique. However, imaging of cranial nerves, especially in healthy volunteers, has received minimal attention. The objectives of this study were to describe the sonographic characteristics of the facial nerve and to establish average values of its diameter. Methods: The extra-cranial part of the facial nerve was scanned bilaterally along its longitudinal axis inside the parotid gland using a 13-MHz probe in 50 healthy adults. The diameter was measured at the nerve’s thickest region. Results: The facial nerve appeared as a thin, tubular, hypoechoic structure inside the parotid gland. The mean facial nerve diameter was 0.5 6 0.1 mm, and the mean side-toside difference in diameter was 0.1 6 0.1 mm. Conclusions: The average facial nerve diameter values may provide help with identification of nerve abnormalities using ultrasound. Muscle Nerve 52: 767–771, 2015
The facial nerve can be affected by various neurological disorders, including Bell palsy, GuillainBarr e syndrome,1,2 and chronic inflammatory demyelinating polyneuropathy.3,4 It is typically assessed with electrodiagnostic (EDX) testing, which may include nerve conduction studies,5 blink reflex recording,6 electromyography,7,8 and magnetic resonance imaging.9 High-resolution ultrasound has emerged as a complementary tool to EDX testing in assessment of neuromuscular disorders; it assesses nerve anatomy,10 detects changes in nerve size in response to different pathologies,11,12 and identifies extrinsic compressive lesions.13 Recent attention has been directed toward exploration of new applications of neuromuscular ultrasound, including its use in cranial nerve assessment.14–17 The optic, facial, vagus, and spinal accessory nerves are the only 4 cranial nerves that can be scanned by ultrasound along part of their extracranial course. The least investigated nerve is the facial nerve; only 1 study has used ultrasound to evaluate the facial nerve in Bell palsy patients,17 whereas other studies have focused on the ultrasound of facial nerveinnervated muscles.18–21 No large scale facial nerve ultrasound study has been conducted on healthy volunteers, and no reference data regarding facial nerve size are available. The aims of this study Abbreviations: EDX, electrodiagnostic Key words: cranial nerve; facial nerve; imaging; nerve diameter; neuromuscular ultrasound Correspondence to: E. A. Tawfik; e-mail: [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 27 February 2015 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.24627
Facial Nerve Ultrasound
were to describe the normal sonographic appearance of the facial nerve and to establish reference values for facial nerve diameter, including side-toside differences in diameter in a large group of healthy volunteers to provide a basis for the identification of facial nerve abnormalities by means of ultrasound. MATERIALS AND METHODS
Fifty healthy volunteers were recruited from hospital employees and the local community. The study was performed in accordance with institutional research regulations and the Helsinki Declaration of 1975. Informed written consent was obtained from all volunteers. A short history was obtained, and a neurological examination was conducted. Any volunteer with a history of Bell palsy, peripheral nervous system disease, or diabetes was excluded. The age, gender, weight, and height were recorded, and body mass index was calculated. Ultrasonography of the facial nerve was performed by the author, who has 1.5 years of experience in neuromuscular ultrasound. The facial nerve was scanned bilaterally in each volunteer using the LOGIQ P5 ultrasound system (General Electric Company, New York, USA) and a 13 MHz linear array transducer. The volunteer was asked to down on the side opposite the scanned side and rest his/her head on a pillow. The extracranial part of the facial nerve was imaged after its exit from the stylomastoid foramen, which is the only part accessible by ultrasound.22 To image the nerve along its longitudinal course inside the parotid gland, the probe was placed transversely immediately under the ear, with the probe orientation marker directed to the sonographer’s left side, i.e., the marker was pointed posteriorly toward the neck when scanning the right facial nerve (Fig. 1A). Care was taken to ensure the probe was at a right angle to the skin, and the pressure applied was minimal at all times. The parotid gland was first identified as a homogenous, relatively hyperechoic structure beneath the skin and subcutaneous tissue, and the facial nerve was subsequently identified as a hypoechoic, thin longitudinal structure inside the gland (Fig. 1B). Moving the probe anteriorly was avoided to prevent potential confusion with the parotid duct (Fig. 1C). The duct lies within the middle half of a line extending from MUSCLE & NERVE
November 2015
767
FIGURE 1. (A) Probe position for facial nerve scanning. The probe is placed just below the ear along the longitudinal course of the facial nerve. The probe is kept in this position at all times. (B) Identification of facial nerve inside the parotid gland. The nerve (straight and curved arrows) appears as a thin tubular structure with a hypoechoic center and hyperechoic border running between the superficial and deep parts of the parotid gland, which appears homogenous and relatively hyperechoic. (C) Anterior position of the probe which should be avoided during nerve scanning to avoid confusion with the parotid duct. (D) Ultrasound image obtained after moving the probe anteriorly as in (C), which shows the parotid duct (multiple arrows) emerging from anterior part of the parotid gland and running superficial to the masseter muscle on its way to the oral cavity.
the tragus to the outer lip.23 It can be distinguished during scanning by following its course from the anterior surface of the parotid gland till it reaches the oral cavity (Fig. 1D). Color and power Doppler was used to ensure that the scanned nerve was not a vascular structure. The facial nerve diameter was measured at the thickest part of the nerve immediately inside its hyperechoic border. Measurement calipers were extended to span between the inner borders of the hyperechoic edges of the nerve (Fig. 2). To image the nerve in a transverse view, the transducer was rotated slowly from the longitudinal axis to the transverse axis. However, capture and clear visualization of the nerve were not possible. The sonographic appearance of the nerve including its shape, course, and echo-texture were 768
Facial Nerve Ultrasound
observed. The mean diameter on each side, the range of values, and the side-to-side differences in diameter were calculated. A comparison of diameters between women and men was tested using a single paired t-test. Correlations between the diameter and each individual’s age, height, weight, and body mass index were tested using Spearman correlation coefficients. A P-value < 0.05 was considered significant. RESULTS
The volunteers included 28 women and 22 men. The ages ranged from 24 to 59 years, mean 36.4 years. The mean height was 161 cm, the mean weight was 74.4 kg, and the mean body mass index was 28.7. The facial nerve sonographic characteristics were consistent in all volunteers; the nerve MUSCLE & NERVE
November 2015
Table 2. Reference values of side-to-side difference in facial nerve diameter Parameter Side-to-side difference (n 5 50)
Min
Max
Mean 6 SD
95% CI
0
0.3
0.1 6 0.1
0.07–0.13
Values are in mm. SD, standard deviation; CI, confidence interval.
FIGURE 2. Ultrasound image showing measurement of facial nerve diameter at its thickest part. The measurement calipers span between the inner borders of the hyperechoic edges of the nerve.
mean 45 years. They scanned the nerve at its emergence from the stylomastoid foramen before it entered the parotid. However, in this study, I scanned the nerve inside the parotid. Lo et al. also measured the diameter differently and calculated the average diameter measured at 3 portions of the nerve: the most proximal portion, most distal portion, and midway through. The mean facial nerve diameter of 50 normal facial nerves they scanned was larger than the measurements obtained in this study (1.4 6 0.2 mm in Lo et al. vs. 0.5 6 0.1 mm in this study). This difference may be attributed to the different methodology regarding scanning and measurements. Lo et al. scanned the nerve at the mastoid region, which was considered to be proximal to the scanning position in this study, and, in general, a nerve is thicker proximally. Additionally, the hyperechoic borders of the nerve were not included in the diameter measurement in this study to avoid errors in measurement. In some volunteers, it was difficult to ascertain the outer rim of the hyperechoic edge of the nerve from the surrounding parotid tissue, which made it difficult to determine its exact outer limit. Therefore, to maintain consistency in measurement, the nerve borders were excluded, which might have resulted in the smaller diameter measurements compared with Lo et al. In their study, the authors did not provide the exact position of the measurement markings; thus, they may have measured the diameter differently. Attempts to include the border in measurements resulted in doubling of the diameter, which demonstrates that nerve size can differ substantially with the inclusion and exclusion of the nerve borders. There was no significant side-to-side difference in diameter. However, the range and mean side-toside differences in diameter in this study may be
appeared as a thin tubular linear structure with a hypoechoic center and hyperechoic border that ran between the superficial and deep parts of the parotid gland (Fig. 1B). The diameter of the nerve on the right side ranged from 0.4 to 0.9 mm, mean 0.5 6 0.1 mm, and the diameter of the nerve on the left side ranged from 0.3 to 0.9 mm, mean 0.5 6 0.1 mm (Table 1). A comparison of the right and left side diameters indicated there was no significant difference (P 5 1.0) (Table 1). The side-to-side differences in diameter ranged from 0 to 0.3 mm, mean 0.1 6 0.1 mm (Table 2). The data analysis obtained from the women and men is shown in Table 3. A comparison of the same-side diameter between the women and men indicated there was no significant difference (right side, P 5 0.79; left side, P 5 0.98). Correlations between the diameter and demographic data of the volunteers, which included age, height, weight, and body mass index, were not significant (Table 4). DISCUSSION
The extracranial part of the facial nerve was readily accessible by means of ultrasound with consistent sonographic characteristics. Only a single study has demonstrated the accessibility of the facial nerve by means of ultrasound and investigated its value for evaluation and prognosis of Bell palsy.16 In that study, Lo et al.16 recruited 37 patients with Bell palsy and 25 healthy volunteers as a control group, 9 of whom were men. The age of their control group ranged from 24 to 71 years,
Table 1. Reference values of facial nerve diameter and side-to-side variability. Right side diameter (n 5 50) Min
Max
Mean 6 SD
0.4
0.9
0.560.1
Left side diameter (n 5 50) 95% CI
Min
Max
Mean 6 SD
0.4760.53
0.3
0.9
0.5 6 0.1
95% CI
P
0.47–0.53
1.0
November 2015
769
Values are in mm. SD, standard deviation; CI, confidence interval.
Facial Nerve Ultrasound
MUSCLE & NERVE
Table 3. Variation in diameter between women and men. Women (n 5 28)
Men (n 5 22)
Side
Min
Max
Mean 6 SD
95% CI
Min
Max
Mean 6 SD
95% CI
Right side Left side
0.4 0.3
0.9 0.8
0.6 6 0.1 0.5 6 0.1
0.56–0.64 0.46–0.54
0.4 0.3
0.7 0.9
0.5 6 0.1 0.5 6 0.2
0.46–0.54 0.42–0.58
P 0.79 0.98
Values are in mm. SD, standard deviation; CI, confidence interval.
of value for identification of abnormalities, especially in unilateral facial nerve lesions. There was no significant difference in the diameters between women and men. Furthermore, the diameter was not significantly correlated with any demographic data. These results indicate the nondependence of facial nerve diameter on gender, age, weight, height, or body mass index. In general, the optimum ultrasonographic assessment of any nerve requires imaging in 2 axes: transverse and longitudinal. The transverse view, which includes measurement of the nerve cross-sectional area, is standard, especially in the assessment of peripheral nerves. However, it may not be applicable in all nerves. In this study, it was only possible to scan the nerve and measure its diameter in the longitudinal view. Capturing the nerve in the transverse section was technically challenging, and measurement of its crosssectional area was not possible. This difficulty may be due to the very small size of the nerve, which makes it difficult to distinguish it in a transverse section. However, in the longitudinal view, the contrast between the nerve’s hypoechogenicity and the homogenous echogenicity of the parotid gland facilitates its identification. Another potential factor is the frequency used (13 MHz) and the resultant resolution, which might not be optimum for distinction of a tiny nerve in the transverse view. The use of a higher frequency to obtain better resolution is worth investigation. This study describes the sonographic appearance of the facial nerve and provides reference values for its diameter in healthy volunteers. These
Table 4. Correlation between facial nerve diameter and demographic data. Right side
Left side
Data
r
P
r
P
Age Height Weight Body mass index
20.07 20.00 20.00 20.00
0.63 1.0 1.0 1.0
0.00 20.01 0.20 0.21
1.0 0.95 0.16 0.14
770
Facial Nerve Ultrasound
findings may be useful for identification of facial nerve abnormalities in various neurological disorders using ultrasound. Comparisons of in vivo ultrasound imaging with imaging in cadavers and an assessment of reproducibility are recommended for future studies. Special thanks to all the volunteers who participated in the study and dedicated their time for the sake of knowledge and science. The abstract has won one of the AANEM 2014 President’s Research Initiative Awards and was presented at the 61st AANEM annual meeting, October 29 to November 1, 2014, in Savannah, GA. REFERENCES 1. .Narayanan RP, James N, Ramachandran K, Jaramillo MJ. GuillainBarr e syndrome presenting with bilateral facial nerve paralysis: a case report. Cases J 2008;1:379. 2. .D’Amore A, Viglianesi A, Cavallaro T, Chiaramonte R, Muscoso EG, Giuffrida S, et al. Guillain-Barr e syndrome associated with acute onset bilateral facial nerve palsies. A case report and literature review. Neuroradiol J 2012;25:665–670. 3. Kokubun N, Hirata K. Neurophysiological evaluation of trigeminal and facial nerves in patients with chronic inflammatory demyelinating polyneuropathy. Muscle Nerve 2007;35:203–207. 4. Varela H, Rubin DI. Facial and trigeminal neuropathies as the initial manifestation of chronic inflammatory demyelinating polyradiculopathy. J Clin Neuromuscul Dis 2009;10:194–198. 5. Lydiatt WM, Sobba-Higley A, Morrow P, Moore GF. Use of electroneuronography in monitoring facial nerve paralysis. Nebr Med J 1992;77:231–234. 6. Kimura J. Electrodiagnosis of the cranial nerves. Acta Neurol Taiwan 2006;15:2–12. 7. Batra SP, Sinha A, Singh NN, Abrol BM. Electro-diagnosis in peripheral facial nerve paralysis. Indian J Otolaryngol 1973;25:76– 86. 8. Grosheva M, Guntinas-Lichius O. Significance of electromyography to predict and evaluate facial function outcome after acute peripheral facial palsy. Eur Arch Otorhinolaryngol 2007;264: 1491–1495. 9. Gupta S, Mends F, Hagiwara M, Fatterpekar G, Roehm PC. Imaging the facial nerve: a contemporary review. Radiol Res Pract 2013;2013: 248039. 10. Meng S, Tinhofer I, Weninger WJ, Grisold W. Anatomical and ultrasound correlation of the superficial branch of the radial nerve. Muscle Nerve 2014;50:939–942. 11. Nakamichi KI, Tachibana S. Enlarged median nerve in idiopathic carpal tunnel syndrome. Muscle Nerve 2000;23:1713–1718. 12. Schreiber S, Abdulla S, Debska-Vielhaber G, Machts J, DannhardtStieger V, Feistner H, et al. Peripheral nerve ultrasound in ALS phenotypes. Muscle Nerve 2014 [Epub ahead of print]. 13. Lai LP, Chen B, Kumar S, Desai R, Mendoza J, Foye PM, et al. Ganglion cyst at the fibular head causing common peroneal neuropathy diagnosed with ultrasound and electrodiagnostic examination: a case report. Am J Phys Med Rehabil 2014;93:824–827. 14. Titlic´ M, Erceg I, Kovacevic´ T, Gabric´ N, Karaman K, Zuljan I, et al. The correlation of changes of the optic nerve diameter in the acute retrobulbar neuritis with the brain changes in multiple sclerosis. Coll Antropol 2005;29:633–636. 15. Cartwright MS, Brown ME, Eulitt P, Walker FO, Lawson VH, Caress JB. Diagnostic nerve ultrasound in Charcot-Marie-Tooth disease type 1B. Muscle Nerve 2009;40:98–102. 16. Lo YL, Fook-Chong S, Leoh TH, Dan YF, Lee MP, Gan HY, et al. High-resolution ultrasound in the evaluation and prognosis of Bell’s palsy. Eur J Neurol 2010;17:885–889.
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17. Lucchetta M, Pazzaglia C, Cacciavillani M, Riondato A, D’Ambrosio CM, Briani C, et al. Nerve ultrasound findings in two cases of spinal accessory nerve palsy. Muscle Nerve 2014;49:293–294. 18. Volk GF, Wystub N, Pohlmann M, Finkensieper M, Chalmers HJ, Guntinas-Lichius O. Quantitative ultrasonography of facial muscles. Muscle Nerve 2013;47:878–883. 19. Alfen NV, Gilhuis HJ, Keijzers JP, Pillen S, Van Dijk JP. Quantitative facial muscle ultrasound: feasibility and reproducibility. Muscle Nerve 2013;48:375–380. 20. Volk GF, Sauer M, Pohlmann M, Guntinas-Lichius O. Reference values for dynamic facial muscle ultrasonography in adults. Muscle Nerve 2014;50:348–357.
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21. Volk GF, Pohlmann M, Sauer M, Finkensieper M, GuntinasLichius O. Quantitative ultrasonography of facial muscles in patients with chronic facial palsy. Muscle Nerve 2014;50:358– 365. 22. Gruber H, Kovacs P. Sonographic anatomy of the peripheral nervous system. In: Peer S, Bodner G, editors. High-resolution sonography of the peripheral nervous system, 2nd ed. Berlin Heidelberg: SpringerVerlag; 2010. p 16. 23. Stringer, Mirjalili SA, Meredith SJ, Muirhead JC. Redefining the surface anatomy of the parotid duct: an in vivo ultrasound study. Plast Reconstr Surg 2012;130:1032–1037.
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The facial nerve can be affected by various neurological disorders, including Bell palsy, GuillainBarr e syndrome,1,2 and chronic inflammatory demyelinating polyneuropathy.3,4 It is typically assessed with electrodiagnostic (EDX) testing, which may include nerve conduction studies,5 blink reflex recording,6 electromyography,7,8 and magnetic resonance imaging.9 High-resolution ultrasound has emerged as a complementary tool to EDX testing in assessment of neuromuscular disorders; it assesses nerve anatomy,10 detects changes in nerve size in response to different pathologies,11,12 and identifies extrinsic compressive lesions.13 Recent attention has been directed toward exploration of new applications of neuromuscular ultrasound, including its use in cranial nerve assessment.14–17 The optic, facial, vagus, and spinal accessory nerves are the only 4 cranial nerves that can be scanned by ultrasound along part of their extracranial course. The least investigated nerve is the facial nerve; only 1 study has used ultrasound to evaluate the facial nerve in Bell palsy patients,17 whereas other studies have focused on the ultrasound of facial nerveinnervated muscles.18–21 No large scale facial nerve ultrasound study has been conducted on healthy volunteers, and no reference data regarding facial nerve size are available. The aims of this study Abbreviations: EDX, electrodiagnostic Key words: cranial nerve; facial nerve; imaging; nerve diameter; neuromuscular ultrasound Correspondence to: E. A. Tawfik; e-mail: [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 27 February 2015 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.24627
Facial Nerve Ultrasound
were to describe the normal sonographic appearance of the facial nerve and to establish reference values for facial nerve diameter, including side-toside differences in diameter in a large group of healthy volunteers to provide a basis for the identification of facial nerve abnormalities by means of ultrasound. MATERIALS AND METHODS
Fifty healthy volunteers were recruited from hospital employees and the local community. The study was performed in accordance with institutional research regulations and the Helsinki Declaration of 1975. Informed written consent was obtained from all volunteers. A short history was obtained, and a neurological examination was conducted. Any volunteer with a history of Bell palsy, peripheral nervous system disease, or diabetes was excluded. The age, gender, weight, and height were recorded, and body mass index was calculated. Ultrasonography of the facial nerve was performed by the author, who has 1.5 years of experience in neuromuscular ultrasound. The facial nerve was scanned bilaterally in each volunteer using the LOGIQ P5 ultrasound system (General Electric Company, New York, USA) and a 13 MHz linear array transducer. The volunteer was asked to down on the side opposite the scanned side and rest his/her head on a pillow. The extracranial part of the facial nerve was imaged after its exit from the stylomastoid foramen, which is the only part accessible by ultrasound.22 To image the nerve along its longitudinal course inside the parotid gland, the probe was placed transversely immediately under the ear, with the probe orientation marker directed to the sonographer’s left side, i.e., the marker was pointed posteriorly toward the neck when scanning the right facial nerve (Fig. 1A). Care was taken to ensure the probe was at a right angle to the skin, and the pressure applied was minimal at all times. The parotid gland was first identified as a homogenous, relatively hyperechoic structure beneath the skin and subcutaneous tissue, and the facial nerve was subsequently identified as a hypoechoic, thin longitudinal structure inside the gland (Fig. 1B). Moving the probe anteriorly was avoided to prevent potential confusion with the parotid duct (Fig. 1C). The duct lies within the middle half of a line extending from MUSCLE & NERVE
November 2015
767
FIGURE 1. (A) Probe position for facial nerve scanning. The probe is placed just below the ear along the longitudinal course of the facial nerve. The probe is kept in this position at all times. (B) Identification of facial nerve inside the parotid gland. The nerve (straight and curved arrows) appears as a thin tubular structure with a hypoechoic center and hyperechoic border running between the superficial and deep parts of the parotid gland, which appears homogenous and relatively hyperechoic. (C) Anterior position of the probe which should be avoided during nerve scanning to avoid confusion with the parotid duct. (D) Ultrasound image obtained after moving the probe anteriorly as in (C), which shows the parotid duct (multiple arrows) emerging from anterior part of the parotid gland and running superficial to the masseter muscle on its way to the oral cavity.
the tragus to the outer lip.23 It can be distinguished during scanning by following its course from the anterior surface of the parotid gland till it reaches the oral cavity (Fig. 1D). Color and power Doppler was used to ensure that the scanned nerve was not a vascular structure. The facial nerve diameter was measured at the thickest part of the nerve immediately inside its hyperechoic border. Measurement calipers were extended to span between the inner borders of the hyperechoic edges of the nerve (Fig. 2). To image the nerve in a transverse view, the transducer was rotated slowly from the longitudinal axis to the transverse axis. However, capture and clear visualization of the nerve were not possible. The sonographic appearance of the nerve including its shape, course, and echo-texture were 768
Facial Nerve Ultrasound
observed. The mean diameter on each side, the range of values, and the side-to-side differences in diameter were calculated. A comparison of diameters between women and men was tested using a single paired t-test. Correlations between the diameter and each individual’s age, height, weight, and body mass index were tested using Spearman correlation coefficients. A P-value < 0.05 was considered significant. RESULTS
The volunteers included 28 women and 22 men. The ages ranged from 24 to 59 years, mean 36.4 years. The mean height was 161 cm, the mean weight was 74.4 kg, and the mean body mass index was 28.7. The facial nerve sonographic characteristics were consistent in all volunteers; the nerve MUSCLE & NERVE
November 2015
Table 2. Reference values of side-to-side difference in facial nerve diameter Parameter Side-to-side difference (n 5 50)
Min
Max
Mean 6 SD
95% CI
0
0.3
0.1 6 0.1
0.07–0.13
Values are in mm. SD, standard deviation; CI, confidence interval.
FIGURE 2. Ultrasound image showing measurement of facial nerve diameter at its thickest part. The measurement calipers span between the inner borders of the hyperechoic edges of the nerve.
mean 45 years. They scanned the nerve at its emergence from the stylomastoid foramen before it entered the parotid. However, in this study, I scanned the nerve inside the parotid. Lo et al. also measured the diameter differently and calculated the average diameter measured at 3 portions of the nerve: the most proximal portion, most distal portion, and midway through. The mean facial nerve diameter of 50 normal facial nerves they scanned was larger than the measurements obtained in this study (1.4 6 0.2 mm in Lo et al. vs. 0.5 6 0.1 mm in this study). This difference may be attributed to the different methodology regarding scanning and measurements. Lo et al. scanned the nerve at the mastoid region, which was considered to be proximal to the scanning position in this study, and, in general, a nerve is thicker proximally. Additionally, the hyperechoic borders of the nerve were not included in the diameter measurement in this study to avoid errors in measurement. In some volunteers, it was difficult to ascertain the outer rim of the hyperechoic edge of the nerve from the surrounding parotid tissue, which made it difficult to determine its exact outer limit. Therefore, to maintain consistency in measurement, the nerve borders were excluded, which might have resulted in the smaller diameter measurements compared with Lo et al. In their study, the authors did not provide the exact position of the measurement markings; thus, they may have measured the diameter differently. Attempts to include the border in measurements resulted in doubling of the diameter, which demonstrates that nerve size can differ substantially with the inclusion and exclusion of the nerve borders. There was no significant side-to-side difference in diameter. However, the range and mean side-toside differences in diameter in this study may be
appeared as a thin tubular linear structure with a hypoechoic center and hyperechoic border that ran between the superficial and deep parts of the parotid gland (Fig. 1B). The diameter of the nerve on the right side ranged from 0.4 to 0.9 mm, mean 0.5 6 0.1 mm, and the diameter of the nerve on the left side ranged from 0.3 to 0.9 mm, mean 0.5 6 0.1 mm (Table 1). A comparison of the right and left side diameters indicated there was no significant difference (P 5 1.0) (Table 1). The side-to-side differences in diameter ranged from 0 to 0.3 mm, mean 0.1 6 0.1 mm (Table 2). The data analysis obtained from the women and men is shown in Table 3. A comparison of the same-side diameter between the women and men indicated there was no significant difference (right side, P 5 0.79; left side, P 5 0.98). Correlations between the diameter and demographic data of the volunteers, which included age, height, weight, and body mass index, were not significant (Table 4). DISCUSSION
The extracranial part of the facial nerve was readily accessible by means of ultrasound with consistent sonographic characteristics. Only a single study has demonstrated the accessibility of the facial nerve by means of ultrasound and investigated its value for evaluation and prognosis of Bell palsy.16 In that study, Lo et al.16 recruited 37 patients with Bell palsy and 25 healthy volunteers as a control group, 9 of whom were men. The age of their control group ranged from 24 to 71 years,
Table 1. Reference values of facial nerve diameter and side-to-side variability. Right side diameter (n 5 50) Min
Max
Mean 6 SD
0.4
0.9
0.560.1
Left side diameter (n 5 50) 95% CI
Min
Max
Mean 6 SD
0.4760.53
0.3
0.9
0.5 6 0.1
95% CI
P
0.47–0.53
1.0
November 2015
769
Values are in mm. SD, standard deviation; CI, confidence interval.
Facial Nerve Ultrasound
MUSCLE & NERVE
Table 3. Variation in diameter between women and men. Women (n 5 28)
Men (n 5 22)
Side
Min
Max
Mean 6 SD
95% CI
Min
Max
Mean 6 SD
95% CI
Right side Left side
0.4 0.3
0.9 0.8
0.6 6 0.1 0.5 6 0.1
0.56–0.64 0.46–0.54
0.4 0.3
0.7 0.9
0.5 6 0.1 0.5 6 0.2
0.46–0.54 0.42–0.58
P 0.79 0.98
Values are in mm. SD, standard deviation; CI, confidence interval.
of value for identification of abnormalities, especially in unilateral facial nerve lesions. There was no significant difference in the diameters between women and men. Furthermore, the diameter was not significantly correlated with any demographic data. These results indicate the nondependence of facial nerve diameter on gender, age, weight, height, or body mass index. In general, the optimum ultrasonographic assessment of any nerve requires imaging in 2 axes: transverse and longitudinal. The transverse view, which includes measurement of the nerve cross-sectional area, is standard, especially in the assessment of peripheral nerves. However, it may not be applicable in all nerves. In this study, it was only possible to scan the nerve and measure its diameter in the longitudinal view. Capturing the nerve in the transverse section was technically challenging, and measurement of its crosssectional area was not possible. This difficulty may be due to the very small size of the nerve, which makes it difficult to distinguish it in a transverse section. However, in the longitudinal view, the contrast between the nerve’s hypoechogenicity and the homogenous echogenicity of the parotid gland facilitates its identification. Another potential factor is the frequency used (13 MHz) and the resultant resolution, which might not be optimum for distinction of a tiny nerve in the transverse view. The use of a higher frequency to obtain better resolution is worth investigation. This study describes the sonographic appearance of the facial nerve and provides reference values for its diameter in healthy volunteers. These
Table 4. Correlation between facial nerve diameter and demographic data. Right side
Left side
Data
r
P
r
P
Age Height Weight Body mass index
20.07 20.00 20.00 20.00
0.63 1.0 1.0 1.0
0.00 20.01 0.20 0.21
1.0 0.95 0.16 0.14
770
Facial Nerve Ultrasound
findings may be useful for identification of facial nerve abnormalities in various neurological disorders using ultrasound. Comparisons of in vivo ultrasound imaging with imaging in cadavers and an assessment of reproducibility are recommended for future studies. Special thanks to all the volunteers who participated in the study and dedicated their time for the sake of knowledge and science. The abstract has won one of the AANEM 2014 President’s Research Initiative Awards and was presented at the 61st AANEM annual meeting, October 29 to November 1, 2014, in Savannah, GA. REFERENCES 1. .Narayanan RP, James N, Ramachandran K, Jaramillo MJ. GuillainBarr e syndrome presenting with bilateral facial nerve paralysis: a case report. Cases J 2008;1:379. 2. .D’Amore A, Viglianesi A, Cavallaro T, Chiaramonte R, Muscoso EG, Giuffrida S, et al. Guillain-Barr e syndrome associated with acute onset bilateral facial nerve palsies. A case report and literature review. Neuroradiol J 2012;25:665–670. 3. Kokubun N, Hirata K. Neurophysiological evaluation of trigeminal and facial nerves in patients with chronic inflammatory demyelinating polyneuropathy. Muscle Nerve 2007;35:203–207. 4. Varela H, Rubin DI. Facial and trigeminal neuropathies as the initial manifestation of chronic inflammatory demyelinating polyradiculopathy. J Clin Neuromuscul Dis 2009;10:194–198. 5. Lydiatt WM, Sobba-Higley A, Morrow P, Moore GF. Use of electroneuronography in monitoring facial nerve paralysis. Nebr Med J 1992;77:231–234. 6. Kimura J. Electrodiagnosis of the cranial nerves. Acta Neurol Taiwan 2006;15:2–12. 7. Batra SP, Sinha A, Singh NN, Abrol BM. Electro-diagnosis in peripheral facial nerve paralysis. Indian J Otolaryngol 1973;25:76– 86. 8. Grosheva M, Guntinas-Lichius O. Significance of electromyography to predict and evaluate facial function outcome after acute peripheral facial palsy. Eur Arch Otorhinolaryngol 2007;264: 1491–1495. 9. Gupta S, Mends F, Hagiwara M, Fatterpekar G, Roehm PC. Imaging the facial nerve: a contemporary review. Radiol Res Pract 2013;2013: 248039. 10. Meng S, Tinhofer I, Weninger WJ, Grisold W. Anatomical and ultrasound correlation of the superficial branch of the radial nerve. Muscle Nerve 2014;50:939–942. 11. Nakamichi KI, Tachibana S. Enlarged median nerve in idiopathic carpal tunnel syndrome. Muscle Nerve 2000;23:1713–1718. 12. Schreiber S, Abdulla S, Debska-Vielhaber G, Machts J, DannhardtStieger V, Feistner H, et al. Peripheral nerve ultrasound in ALS phenotypes. Muscle Nerve 2014 [Epub ahead of print]. 13. Lai LP, Chen B, Kumar S, Desai R, Mendoza J, Foye PM, et al. Ganglion cyst at the fibular head causing common peroneal neuropathy diagnosed with ultrasound and electrodiagnostic examination: a case report. Am J Phys Med Rehabil 2014;93:824–827. 14. Titlic´ M, Erceg I, Kovacevic´ T, Gabric´ N, Karaman K, Zuljan I, et al. The correlation of changes of the optic nerve diameter in the acute retrobulbar neuritis with the brain changes in multiple sclerosis. Coll Antropol 2005;29:633–636. 15. Cartwright MS, Brown ME, Eulitt P, Walker FO, Lawson VH, Caress JB. Diagnostic nerve ultrasound in Charcot-Marie-Tooth disease type 1B. Muscle Nerve 2009;40:98–102. 16. Lo YL, Fook-Chong S, Leoh TH, Dan YF, Lee MP, Gan HY, et al. High-resolution ultrasound in the evaluation and prognosis of Bell’s palsy. Eur J Neurol 2010;17:885–889.
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