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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 5  |  Issue : 4  |  Page : 100-106

High frequency ultrasonography of the facial nerve: Another effective method to observe the course of idiopathic facial nerve paralysis


1 Departments of Neurology, Beijing Luhe Hospital, Capital Medical University, Beijing, China
2 Interventional and Pain, Beijing Luhe Hospital, Capital Medical University, Beijing, China
3 Research and Development, Beijing Luhe Hospital, Capital Medical University, Beijing, China
4 China-America Institute of Neuroscience, Beijing Luhe Hospital, Capital Medical University, Beijing, China

Date of Submission23-Sep-2020
Date of Decision27-Oct-2020
Date of Acceptance18-Nov-2020
Date of Web Publication31-Dec-2020

Correspondence Address:
Dr. Xiaokun Geng
Department of Neurology, Beijing Luhe Hospital, Capital Medical University, No. 82 Xinhua South Road, Tongzhou District, Beijing 101149
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ed.ed_30_20

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  Abstract 


Objective: This study was designed to investigate and compare both ultrasonographic and electrophysiological methods of examination of the facial nerve in idiopathic facial paralysis (IFP).
Materials and Methods: Patients with IFP diagnosed between January 2018 and June 2019 (n = 178) underwent ultrasonographic and electrophysiological examinations of the facial nerve, within the 1st week of symptoms and every 1–3 following weeks until asymptomatic, with comparisons between the affected and unaffected sides.
Results: There were significant differences in the ultrasonographic diameter and the electrophysiological results obtained from the facial nerve between the affected and unaffected sides. Ninety-one patients completed follow-up and underwent re-examination of the facial nerve by ultrasonography and/or electromyography. The difference between the affected and unaffected sides in terms of the ultrasonographic diameter of the facial nerve gradually decreased with the course of the disease. The ultrasonographic diameter of the facial nerve of the affected side was greater by 0.3 mm than that of the unaffected side for more than 3 weeks, indicative of a poor prognosis, which was consistent with the electrophysiological results.
Conclusions: The combination of ultrasonographic and electrophysiological examinations of the facial nerve serves to better guide clinical treatment and assess the prognosis of IFP.

Keywords: Electrophysiology, idiopathic facial paralysis, ultrasonography


How to cite this article:
Zhu J, Li X, Han Y, Cao Y, Guan L, Geng X. High frequency ultrasonography of the facial nerve: Another effective method to observe the course of idiopathic facial nerve paralysis. Environ Dis 2020;5:100-6

How to cite this URL:
Zhu J, Li X, Han Y, Cao Y, Guan L, Geng X. High frequency ultrasonography of the facial nerve: Another effective method to observe the course of idiopathic facial nerve paralysis. Environ Dis [serial online] 2020 [cited 2022 Jun 25];5:100-6. Available from: http://www.environmentmed.org/text.asp?2020/5/4/100/305711




  Introduction Top


Idiopathic facial paralysis (IFP), also known as Bell's palsy or facial neuritis, is peripheral facial paralysis caused by nonspecific inflammation of the facial nerves in the stylomastoid foramen. IFP is a common mononeuropathy of the facial nerve. It occurs globally and at any age but is more common in young people. In general, IFP can be diagnosed by a neurologist based on medical history and clinical presentation. In special cases, it is necessary to use supplementary examinations such as head magnetic resonance imaging (MRI) and electrophysiological examinations to differentiate the disease and further confirm the diagnosis. Most patients have a good prognosis, while some have mild sequelae, and others have significant deficits. However, the appearance and the function of muscles involved in facial expression are affected in patients with poor prognoses, which can negatively influence the patient's mental health and daily life. Therefore, prognostic predictions are often an issue facing clinicians.

The majority of previous studies have used electrophysiological examinations to assist in the diagnosis of IFP and to assess disease severity and prognosis, with examinations including components such as the blink reflex, facial nerve conduction, F-wave, and facial muscle needle electromyography (EMG). It is believed that the blink reflex has a higher sensitivity in early diagnosis as it reflects the abnormality of the entire facial nerve.[1] In addition, facial electroneurography that measures the decline rate of facial muscle compound muscle action potential (CMAP) amplitude is more meaningful for prognostic assessment, whereby a decline of >90% in amplitude would suggest a poor prognosis.[2],[3],[4] Currently, many imaging studies have been conducted on this disease, in which a number of diagnostic approaches such as enhanced computerized tomography and MRI are employed and have revealed abnormalities in the proximal end of the facial nerve.[5],[6] However, these examination methods are costly and time consuming, thereby generally limiting the methods for differential diagnoses and surgical evaluation in the sequelae stage,[7],[8],[9] making them unsuitable for acute phase observation, re-examination, and evaluation.

In recent years, the rapid development of high-frequency neuro-ultrasound has received increased attention in the diagnosis of neuromuscular diseases. This method was first used for the diagnosis of compression diseases such as compression neuropathy, peripheral nerve tumors, or nerve cysts[10] and is helpful for preoperative evaluation of orthopedic surgery and neurosurgery. In the field of neurology, the combination of electrophysiology and neuro-ultrasound is widely used in the differential and assisted diagnoses of acute and chronic inflammatory demyelinating polyradiculoneuropathy, hereditary motor-sensory neuropathy, and hereditary neuropathy with liability to pressure palsies.[11],[12],[13],[14],[15],[16],[17] Of the cranial nerves, the optic, facial, vagus, and accessory nerves can also be imaged at some points along their course,[18] but there are relatively few studies to date. Studies on facial nerves and especially on IFP usually involve comparative analyses between a case group and a control group. Results from these studies suggest that the facial nerve diameters measured with high-frequency ultrasound are significantly different between the case group and the healthy control group, as well as between the unaffected and affected sides of the case group; the difference is likely to facilitate prognostic prediction to some extent.[10],[11],[12],[13],[14],[15],[16],[17],[18] However, these studies only included a small number of cases and did not re-examine dynamic structural changes of the facial nerve using ultrasonography during the course of the disease.

In this study, 178 patients with IFP were included. Facial nerves were examined with ultrasonography and electrophysiology and were re-examined at follow-up. High-frequency ultrasonography was used to observe the structural changes of the proximal end of the facial nerve in the acute stage of IFP and to explore the clinical application value of high-frequency ultrasound and its correlation with electrophysiological results.


  Materials and Methods Top


General information

We recruited 178 patients with IFP diagnoses in our hospital between January 2018 and June 2019. There were 101 males and 77 females, aged 14–81 years with a mean age of 46.54 years. Inclusion criteria were as follows: patients who presented with symptoms meeting the neuropathologic diagnostic criteria for IFP and had an acute disease onset within 7 days of admission without undergoing any treatment. Exclusion criteria were as follows: patients who presented with traumatic facial nerve injury, central facial paralysis, facial paralysis secondary to tumor or other causes, or presented with multiple cranial neuritides caused by viral infection. Each patient was diagnosed by an experienced neurologist, and patients with no contraindications were treated with prednisone at a starting dose of 30 mg for 10 days. B vitamins were administered from onset to remission of symptoms. Sixty-eight patients were treated with antiviral therapy according to the guidelines by the attending physician.[19]

Instrumental methods and judgment criteria

Ultrasonography was performed using a Hitachi Ascendus ultrasound system with an 18-MHz linear array probe. The patient is relaxed lying on his back on the examination bed with his face and neck fully exposed. Turn the head to the other side of the check. Below the earlobe, the probe is oblique to the direction of the osseous external auditory canal, and the facial nerve with high and low echoes can be scanned in the triangular region surrounded by the three points of the osseous external auditory canal, mastoid process, and parotid gland. Along the direction of nerve path, the probe is probed to the part before entering the parotid gland, namely, the diameter of the nerve trunk near the end face after exiting the stem-milk foramina [Figure 1].
Figure 1: The method of high frequency ultrasonography examination in longitudinal planes in the study. The patient is relaxed lying on his back on the examination bed with his face and neck fully exposed. Turn the head to the other side of the check. Below the earlobe, the probe is oblique to the direction of the osseous external auditory canal, and the facial nerve with high and low echoes can be scanned in the triangular region surrounded by the three points of the osseous external auditory canal, mastoid process, and parotid gland. Along the direction of nerve path, the probe is probed to the part before entering the parotid gland, namely, the diameter of the nerve trunk near the end face after exiting the stem milk foramina (a,b,c)

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Imaging physicians perform image acquisition and data measurement. Since few studies have been conducted on facial nerve ultrasonography and there is no established consensus on a normal range of ultrasonographic examination results, a strategy for comparing the affected to the unaffected side was adopted in this study [Figure 2].
Figure 2: The ultrasonic manifestations of bilateral nerve in one patient were as follows: the diameter of the right side (a) of the nerve was 0.8 mm, and the longitudinal section showed hyperechoic and hypoechoic intersections, showing the echo of the epineurium and nerve bundles; the left side (b) was the affected side, with the diameter of the facial nerve 1.0 mm (FN: Facial nerve; PA: Parotid gland; MAS: mastoid)

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EMG was performed using a Keypoint EMG device (Dantec Medical Inc., Denmark) with a surface electrode. Due to large variations in the normal ranges of the latent period, amplitude, and F-wave in the facial nerve EMG, the affected side was compared to the unaffected side in terms of blink reflex and facial nerve CMAP amplitude, which is a widely accepted assessment method that can minimize the interference from gender, age, underlying diseases, and other factors.

The blink reflex was assessed by applying stimulation to the supraorbital branch of the trigeminal nerve at the superior orbital fissures on both sides and recording the electrical activity of the bilateral orbicularis oculi muscle with the reference electrodes on the temporalis muscle, to allow for the R1 wave and bilateral R2 waves to be recorded. Disappearance of waveforms or a delayed latency (R1: >12 ms; R2: >35 ms) was considered indicative of an abnormality. The stimulator's frequency band-pass filter range was set from 20 Hz to 10 kHz, the sensitivity was set to 0.1 mV/D, and the pulse current was set to have a duration of 0.2 ms with an intensity of 10–20 mA. Stimulation was performed at least four times, and stable waveforms with good reproducibility were chosen for measurement, with the results reported as an average.

For examination of facial nerve conduction, the amplitude of CMAP was recorded, which was divided into three parts: (1) applying vestibular stimulation and recording signals at the ipsilateral orbicularis oculi muscle with a reference electrode on the contralateral orbicularis oculi muscle, (2) applying stimulation to the frontal branch of the facial nerve and recording signals from the ipsilateral frontalis muscle with a reference electrode on the contralateral frontalis muscle, and (3) applying stimulation to the mandibular branch of the facial nerve and recording signals from the ipsilateral mentalis muscle with a reference electrode on the contralateral mentalis muscle. Peak-to-peak amplitude was recorded following stimulation. The stimulator was set to have a frequency band-pass filter of 2 Hz to 10 kHz, a sensitivity of 5 mV/D, and a pulse current with a duration of 0.2 ms. The stimulation intensity was gradually increased from the minimum current until the maximum CMAP amplitude was elicited, after which the current was further increased by 10%–30% to generate a supramaximal response. Next, a stable waveform was selected for measurement to record amplitudes from both sides. The percentage decrease of amplitude from the affected side relative to the unaffected side was calculated, and a percentage decrease more than 30% was considered indicative of abnormality.[20] All electrophysiological examinations were performed by the same neurologist, who possessed years of operational experience and who was also an electrophysiologist [Figure 3].
Figure 3: The method of nerve conduction for the facial nerve in the study

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Classification of facial nerve function was performed according to the House–Brackmann Facial Nerve Function Grading Scale recommended by the Facial Nerve Disorders Committee of the American Academy of Otolaryngology and Head and Neck Surgery. The severity of facial nerve paralysis was classified into 1–6 grades, with Grades 1–3 indicating an early stage with mild symptoms and Grades 4–6 indicating severe symptoms. Indication for good prognosis was symptomatic alleviation within 3 months (Grades 1–2). Indication for poor prognosis was the presence of obvious symptoms after 3 months (Grades ≥3).

Statistical analyses were performed using SPSS version 22.0 (IBM Corp., Armonk, NY) statistical analysis software. Measurement data were expressed as mean ± standard deviation. Mean comparison between the affected side group and the unaffected side group was performed using a paired sample t-test. Comparison of the ultrasound diameter of the facial nerve among the three different follow-up periods was performed using a repeated-measures analysis of variance (ANOVA). Statistical significance was set to P < 0.05.


  Results Top


A total of 178 IFP patients were included in this study, each of whom completed at least one facial nerve ultrasound examination, 138 of whom completed electrophysiological examination, and 91 of whom completed three facial nerve ultrasound examinations within 1 week of onset, 2–3 weeks after onset, and 3 weeks after onset. Among the 178 patients, 173 had a good prognosis, only 5 had a poor prognosis, and still had obvious sequelae at 3 months.

Electrophysiological presentation of the facial nerve

The blink reflex showed that the affected side in the early stage presented with abnormality; specifically, the waveform of the affected side could not be elicited or its latent period was longer than that of the contralateral side. Over the period of the study, however, the abnormality gradually disappeared. There were statistically significant differences between the CMAP amplitudes at the three points, which was consistent with the results of previous studies [Table 1].
Table 1: Compound muscle action potential amplitudes at different nerve locations

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Ultrasonographic presentation of the facial nerve

All of 178 cases of patients underwent the first round of facial nerve ultrasonography within 1 week of onset. The ultrasonographic results showed that the diameters of the longitudinal section of the facial nerve ranged from 0.8 to 1.8 mm in the affected side with a mean of 1.24 ± 0.23 mm. The diameters of the longitudinal section of the facial nerve ranged from 0.5 to 1.4 mm in the unaffected side with a mean of 0.89 ± 0.17 mm. The difference between the affected and unaffected sides was statistically significant (P < 0.05), which was consistent with the results of previous studies.[21],[22],[23],[24] Most of the healthy lateral nerves showed intrathecal isoechoic, hypoechoic in the injured side.

In 178 patients with 91 cases, respectively, in within 1 week, 2–3 weeks, and 3 weeks after onset to complete three facial nerve ultrasound examinations, the application of repetitive measure anova statistical analysis result difference was statistically significant [Table 2], along with the development of the course, namely, facial nerve can be seen through the facial nerve of high-frequency ultrasound in diameter from the changing process of edema enlargement to return to normal. For five patients with poor prognoses, the ultrasonographic diameter of the facial nerve of the affected side was greater by 0.3 mm than the unaffected side for more than 3 weeks, and the CMAP amplitude of the affected side was decreased by >90% compared to the unaffected side. Results for the two methods of examination were in agreement. Therefore, the obvious enlargement of the diameter of facial nerve ultrasound over 3 weeks may indicate a poor prognosis. Since most patients with this disease have a good prognosis, the number of patients with poor prognosis collected in the study is small, so the accurate conclusion of poor prognosis can be further observed and studied.
Table 2: Facial nerve ultrasonography differences over time

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  Discussion Top


In this study, high-frequency ultrasound was used to observe the proximal structure of the nerve outside the stylomastoid foramen in patients with IFP, and the differences in the bilateral nerves in patients with IFP were confirmed, and the dynamic changes at different stages in the course of the disease could be seen through multiple examinations. Several previous studies on facial nerve ultrasound examination for idiopathic facial palsy have shown inconsistent results, possibly due to methodological differences.

Tawfik et al. observed 12 patients with Bell's palsy and 20 healthy controls. Before the study, an autopsy was performed to verify and ensure the accuracy of neuro-ultrasound. Meanwhile, the diameter of the facial nerve, vagus nerve cross-sectional area, and frontalis muscle thickness were also measured in the patients with Bell's palsy in the same study. The vagus nerve cross-sectional area and frontalis muscle thickness were not statistically different from those in the control group, verifying that facial neuropathy occurs independently in Bell's palsy and does not fall in the category of extensive cranial neuropathy. In addition, the study highlighted that facial nerve ultrasonography is of limited usefulness for the definitive diagnosis of Bell's palsy.[21] It would have been interesting if the study combined facial nerve ultrasonography with an electrophysiological examination to see how the measures compared. Lo et al. reported 37 patients with Bell's palsy and 25 healthy controls, finding that the facial nerve diameter of the affected side was significantly different from that of the healthy control; it revealed that standard ultrasound accurately predicted a good prognosis (100%) and was superior – in terms of prediction accuracy – to the latency of facial nerve conductance, the amplitude, and the blink reflex, and that abnormal ultrasonographic results predicted poor prognoses (77%), indicating its superiority to electrophysiological examinations.[22] In our study, 25 patients underwent facial nerve ultrasonography multiple times during the course of the disease and their facial nerves were found to not be significantly thickened or swollen. The 25 participants consisted of 19 with mild symptoms, 5 with severe symptoms, and 1 with a poor prognosis (Grades >2 at 3 months). One possible explanation for the discrepancy between the two studies may be due to the location of related to some lesions, specifically those that were located at the proximal end outside the stylomastoid foramen, such as at the geniculate ganglion in the facial nerve canal, beyond the scope of ultrasonographic detection.

Twenty patients with IFP were recruited in another study, where they underwent ultrasonographic and electrophysiological examinations of the facial nerves within 2 weeks of disease onset and at 1 month following onset, respectively. Ultrasonography was performed at three locations consisting of a proximal end, a distal end, and a mid-point. Comparison between the affected and unaffected sides revealed that there was no statistically significant difference in ultrasonographic diameter at the three points in the early stage (within 2 weeks), and the measurement results of ultrasonographic diameter failed to predict the prognosis. However, when the three points were re-examined with ultrasonography at 1 month after disease onset, the diameter at the mid-point and CMAP amplitude were associated with prognosis.[24] However, Li et al. reported that no association was found between the two examinations.[23]

In our study, facial nerve diameter was measured outside the stylomastoid foramen, specifically at the proximal end, with observation made on five patients with poor prognoses. The ultrasonographic facial nerve diameter of the affected side was significantly greater by 0.3 mm than that of the unaffected side for more than 3-week disease onset, and the CMAP amplitude of the affected side was more than 90% lower than that of the unaffected side. This demonstrates similar examination results for both ultrasonographic and electrophysiological measures of IFP. Therefore, the presence of an ultrasonographic diameter of the facial nerve that is significantly greater than normal for more than 3 weeks may indicate a poor prognosis. As the majority of patients with this disease have a good prognosis and the number of the included patients with poor prognoses was small in our study, further observations are needed to verify the above conclusion regarding the ultrasonographic diameter-based prediction accuracy of poor prognoses.

In addition, two patients in the study did not receive steroid therapy in the early stage of the disease due to relative contraindications. In these patients, symptoms were not improved significantly after 1 week. Further, the ultrasonography revealed that the facial nerves of the affected side were clearly swollen. After the second round of ultrasonography, oral administration of a small dose of steroids was tentatively conducted in order to alleviate neural edema and improve clinical symptoms, and a dynamic observation of the results of facial nerve ultrasonography was made. Finally, ultrasound examination on the 50th and 76th day of the disease showed that the facial nerve returned to normal, and the facial nerve function also returned to grade 2, with a good prognosis. [Table 3]. The results suggest that dynamic observation of changes in facial nerve diameter may be of significance for guiding clinical treatment.
Table 3: Two patients with poor prognosis in different periods of the facial nerve diameter changes

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  Conclusions Top


This study showed that ultrasonography is an effective tool in addition to the electrophysiologic methods to observe the clinical course of Bell's palsy. Some patients likely had lesions at the proximal end of the facial nerve, thus specific ultrasonographic presentations were not observed. However, it is still possible to conduct the examination in the early course of the disease in order to perform the dynamic observation of patients who undergo symptom changes and even to guide treatment if necessary. During the course of the disease, electrophysiological examinations of the facial nerves reflect the physiological characteristics of the facial nerves. Structural changes are directly observed with ultrasonography, which is noninvasive, painless, and more cost-effective than MRI. The two examinations are complementary to each other, and their combination provides a more objective approach for guiding clinical treatment and making prognostic predictions.

Ethics approval

The study was approved by the Ethics Committee of Beijing Luhe Hospital affiliated to Capital Medical University (Approval Number: 2020-LHKY-052-01; Date of Approval: October 15th, 2020).

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.



 
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