Growth of muscles and nerves in the upper eyelid: a morphometrical and immunohistochemical study using term human fetuses.

BACKGROUND: There is no information about muscle growth in eyelids with infrequent blinking in fetuses. METHODS: To examine the muscle and nerve morphology, we morphometrically and immunohistochemically examined sagittal sections of unilateral upper eyelids obtained from 21 term fetuses (approximately 30-42 weeks of gestation) and, for the comparison, those from 10 midterm fetuses (12-15 weeks). RESULTS: The approximation margin of the upper eyelid always corresponded to the entire free margin in midterm fetuses, whereas it was often (18/21) restricted in the posterior part in term fetuses. Thus, in the latter, the thickness at the approximation site to the lower lid often ranged from 0.8 to 1.6 mm and corresponded to 18-56% of the nearly maximum thickness of the lid. In the lower part of the upper eyelid, a layer of the orbicularis oculi muscles often (14/21) provided posterior flexion at 90-120° to extend posteriorly. Nerve fibers running along the mediolateral axis were rich along the approximation surface at term, but they might not be reported in the upper eyelid of adults. CONCLUSION: Being different from adult morphologies, the term eyelid was much thicker than the approximation surface and it carried a flexed muscle layer and transversely-running nerve. The infrequent blinking in fetuses seemed to provide a specific condition for the muscle-nerve growth. Plastic and pediatric surgeons should pay attention to a fact that infants' upper eyelid was unlikely to be a mini-version of the adult morphology.

Future treatment options for facial nerve palsy: a review on electrical stimulation devices for the orbicularis oculi muscle.

Facial nerve palsy can cause diminished eyelid closure (lagophthalmos). This occurs due to functional deficits of the orbicularis oculi muscle, potentially leading to sight-threatening complications due to corneal exposure. Current management options range from frequent lubrication with eye drops, to the use of moisture chambers and surgery. However, achieving functional restoration may not always be possible. Recent efforts have been directed towards the support of orbicularis oculi muscle function through electrical stimulation. Electrical stimulation of the orbicularis oculi muscle has been demonstrated as feasible in human subjects. This article offers a comprehensive review of electrical stimulation parameters necessary to achieve full functionality and a natural-looking eye blink in human subjects. At present, readily available portable electrical stimulation devices remain unavailable. This review lays the foundation for advancing knowledge from laboratory research to clinical practice, with the ultimate objective of developing a portable electrical stimulation device. Further research is essential to enhance our understanding of electrical stimulation, establish safety standards, determine optimal current settings, and investigate potential side effects.

Distribution patterns of infraorbital nerve branches and risk for injury.

BACKGROUND: During oral and head and neck surgery, oral vestibular incisions may require a transverse incision on the upper lip mucosa, resulting in possible sensory disturbances in the area innervated by infraorbital nerve (ION) branches. Although sensory disturbances are attributed to nerve injuries, anatomy textbooks have not showed the precise distribution patterns of the ION branches in the upper lip. Furthermore, no detailed study has been available on this issue. This study aimed to reveal the precise distribution patterns of ION branches in the upper lip by dissecting the detached upper lip and cheek area using a stereomicroscope. METHODS: During a gross anatomy course at Niigata University (2021-2022), nine human cadavers were examined with special focus on the relationship between ION branches in the upper lip and the layered structure of facial muscles. RESULTS: The ION branched to the inferior palpebral (IP), external and internal nasal, and superior labial (lateral and medial) nerves. The ION branches in the upper lip did not run in a horizontal pattern from outside to inside but showed a predominantly vertical pattern. Considering their course, incising the upper lip mucosa transversely may cause paresthesia of the ION branches. The internal nasal (IN) and medial superior labial (SLm) branches tended to penetrate the orbicularis oris and descend between this muscle and labial glands, whereas the lateral superior labial (SLl) branches tended to innervate the skin. CONCLUSIONS: These findings suggest that a lateral mucosal incision is recommended for oral vestibular incisions of the upper lip and that deeper incisions to the labial glands should be avoided when incising the medial side to preserve the ION during surgery from an anatomical point of view.

Lower Facial Nerve Nomenclature Clarification: Cervical Branch Controls Smile-Associated Lower Lip Depression and Dental Display.

OBJECTIVE: In head and neck ablative surgery, traditional teaching is that the key facial nerve branch to preserve along the plane of the lower border of the mandible is the marginal mandibular branch (MMb), which is considered to control all lower lip musculature. The depressor labii inferioris (DLI) is the muscle responsible for pleasing lower lip displacement and lower dental display during natural emotive smiling. STUDY DESIGN: To understand the structure/function relationships of the distal lower facial nerve branches and lower lip musculature. SETTING: In vivo extensive facial nerve dissections under general anesthesia. METHODS: Intraoperative mapping was performed in 60 cases, using branch stimulation and simultaneous movement videography. RESULTS: In nearly all cases, the MMb innervated the depressor anguli oris, lower orbicularis oris, and mentalis muscles. The nerve branches controlling DLI function were identified 2 ± 0.5 cm below the angle of the mandible, originating from a cervical branch, separately and inferior to MMb. In half of the cases, we identified at least 2 independent branches activating the DLI, both within the cervical region. CONCLUSION: An appreciation of this anatomical finding may help prevent lower lip weakness following neck surgery. Avoiding the functional and cosmetic consequences that accompany loss of DLI function would have a significant impact on the burden of potentially preventable sequelae that the head and neck surgical patient frequently carries.

V to VII Nerve Transfer for Smile Reanimation.

Using the wording "facial reanimation," surgeons mean restoring movements to the paralyzed face. According to the condition of mimic muscle, facial palsy can be classified as recent (mimic muscle still alive) and chronic (atrophy of mimic muscle) palsy. The treatment is quite different because in the former group the mimic muscles can be still used so long as a new motor source would be connected to the damaged facial nerve. In the latter group, muscular transplantation is needed to substitute the atrophied mimic muscles of the middle part of the face. In both cases, the neural impulse that makes the muscles (mimic muscle in the former, transplanted muscle in the latter) move come from a new motor nerve. Nowadays, the masseteric nerve is widely used as a new motor source in recent facial reanimation; the same nerve has also a main role in the treatment of both chronic facial palsy where it is used as the new nervous stimulus for the new transplanted muscle and facial paresis where the nervous stimulus coming from the masseteric nerve is used to empower the stimulus coming from the injured facial nerve. The masseteric nerve can be usually connected directly to the facial nerve without the interposition of a nerve graft, with a faster reinnervation. Moreover, the use of the masseteric nerve gives no morbidity to the masticatory functions.

Feasibility of facial nerve monitoring using adhesive surface electrodes during parotidectomy: a comparative study with needle electrodes.

PURPOSE: Electrophysiological monitoring of the facial nerve during parotidectomy has been reported as an adjunctive method to prevent facial nerve injury. Classically, a needle electrode is used to obtain electromyographic (EMG) signals from facial muscles during facial nerve monitoring (FNM) of parotid surgery, likewise adhesive surface electrodes. This study aimed to investigate the feasibility of performing FNM with surface electrodes during parotid surgery and to compare EMG values with needle electrodes. METHODS: Thirty patients who underwent parotidectomy under FNM using adhesive surface and needle electrodes were included. Two pairs of adhesive surface electrodes and needle electrodes were used for FNM during parotid surgery. Mean amplitudes were collected after electrical facial nerve stimulation at 1 mA after specimen removal. RESULTS: The mean amplitude of the adhesive surface electrodes was 226.50 ± 118.44 µV (orbicularis oculi muscle) and 469.6 ± 306.06 µV (orbicularis oris muscle), respectively. The mean amplitude of the needle electrodes was 449.85 ± 248.10 µV (orbicularis oculi muscle) and 654.66 ± 395.71 µV (orbicularis oris muscle), respectively. The mean amplitude of the orbicularis oris muscle was significantly greater than that of the orbicularis oculi. The amplitude values measured in the orbicularis oculi muscle showed significant differences between the needle and skin electrodes. CONCLUSIONS: Facial nerve monitoring (FNM) using adhesive surface electrodes is feasible in parotid surgery. Although the mean amplitude value of the surface electrode was relatively lower than that of the needle electrode, the surface electrode is considered a feasible and safe EMG recording device for FNM in parotid surgery.

Significant Correlation between Delayed Relief after Microvascular Decompression and Morphology of the Abnormal Muscle Response in Patients with Hemifacial Spasm.

Although microvascular decompression (MVD) is a reliable treatment for hemifacial spasm (HFS), postoperative delayed relief of persistent HFS is one of the main issues. In patients with hemifacial spasm, stimulation of a branch of the affected facial nerve elicits an abnormal response in the muscles innervated by another branch. Several specific types of waves were found in the abnormal muscle response (AMR). This study aimed to confirm the relationship between the initial morphology of the AMR wave and delayed relief of persistent HFS after MVD. We retrospectively analyzed and compared the data from 47 of 155 consecutive patients who underwent MVD for HFS at our hospital between January 2015 and March 2020. Based on the pattern of the initial AMR morphology on orbicularis oculi and mentalis muscle stimulation, patients were divided into two groups, namely, the monophasic and polyphasic groups. The results of MVD surgery for HFS were evaluated 1 week, 1 month, and 1 year postoperatively, by evaluating whether or not the symptoms of HFS persisted at the time of each follow-up. There were significantly higher rates of persistent postoperative HFS in patients with the polyphasic type of initial AMR at 1 week and 1 month after the surgery (p < 0.05, respectively), as assessed using Yates chi-squared test and Fisher's exact test. A significant correlation was observed between delayed relief after MVD and polyphasic morphology of the AMR in electromyographic analysis in patients with hemifacial spasm.

Refined Concept of Motor Supply to the Medial Periorbital Area Relevant to Periorbital Surgery.

BACKGROUND: Mimetic muscles in the medial periorbital area have been thought to be innervated solely by the angular nerve. Recently, however, the upper medial palpebral branch and lower palpebral branch were reported as additional motor suppliers in this area. This study aimed to define all the motor nerve systems passing through the medial canthal area. METHODS: Motor nerve branches that passed through the medial canthal region were identified and traced thoroughly from the parotid gland to their destinations under a surgical microscopic field in 74 hemifaces. The courses, anatomical positions of, and anatomical relationships between the angular nerve and the upper medial palpebral branch were observed. RESULTS: The upper medial palpebral branch and the angular nerve were found in all samples within a 3-mm to 6-mm area lateral to the intersecting point of the medial orbital rim and medial canthal ligament. The upper medial palpebral branch supplied the upper eyelid, whereas the angular nerve supplied the extraorbicularis muscles in the medial periorbital area. The medial pretarsal area of the upper eyelid was supplied solely by the pretarsal branches of the upper medial palpebral branch, which was formed by uniting three or four minor branches that traveled throughout the anterior cheek. CONCLUSIONS: Two separate motor nerve systems, the upper medial palpebral branch and the angular nerve, exist in the medial canthal area. The upper medial palpebral branch course along the medial orbital rim is considered as a facial nerve danger zone.

Surgical Treatment for Postparalytic Facial Synkinesis: A 35-Year Experience.

BACKGROUND: Surgical intervention with combined myectomy and neurectomy followed by functioning free muscle transplantation has been proposed to effectively resolve the problem of postparalytic facial synkinesis since 1985, and it continues to be the authors' standard of care. The authors aim to provide evidence that this surgical strategy is effective for treatment of synkinesis and smile quality. METHODS: One hundred three patients with postparalytic facial synkinesis were investigated (1985 to 2020). They all underwent extensive removal of the synkinetic muscles and triggered facial nerve branches in the cheek, nose, and neck regions, followed by gracilis functioning free muscle transplantation for facial reanimation. Ninety-four patients (50 with type II and 44 with type III postparalytic facial synkinesis), all of whom had at least 1 year of postoperative follow-up, were included in the study. Patient demographics and functional and aesthetic evaluations before and after surgery were collected. RESULTS: In the yearly distribution of the facial paralysis reconstruction, the incidence of surgical intervention increased from 15 percent before 2012 up to 24 percent in the years after. Young adults (79 percent) and female patients (63 percent) were the dominant population. Results showed a significant improvement of the facial smile quality, with more teeth visible while smiling, and a long-lasting decrease of facial synkinesis. Ninety-six percent of patients did not require botulinum toxin type A injection after surgery. Revision surgery for secondary deformity was 53 percent. CONCLUSIONS: Combined myectomy and neurectomy followed by functioning free muscle transplantation for type II and III synkinetic patients leads to promising and long-lasting results despite high revision rates. Refined techniques to decrease the revision rates are needed in the future. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

Muscle Fiber Composition Changes after Selective Nerve Innervation.

Facial nerve paralysis interferes with mimetic muscle function. To reconstruct natural facial movement, free muscle flaps are transplanted as new muscles. However, it is difficult to maintain resting tonus. A dual innervation technique in which other nerves such as the hypoglossal nerve or contralateral facial nerve are added is often applied. Using 10-week-old rats (n = 10), the masseteric and hypoglossal nerves were cut, and the distal stump of the masseteric nerve and the proximal stump of the hypoglossal nerve were then sutured (suture group). In the other group, the masseteric nerve was cut and cauterized (cut group). Immunohistochemistry and microarray were performed on the extracted masseter muscle. The immunohistochemistry results suggested that the muscles in the suture group obtained oxidative characteristics. The microarray showed the genes involved in mitochondrial function, including Perm1. In summary, our data support the validity of the dualinnervation technique for facial paralysis treatment.

Inhibiting Matrix Metalloproteinases Protects Evoked Electromyography Amplitudes and Muscle Tension in the Orbicularis Oris Muscle in a Rat Model of Facial Nerve Injury.

Facial nerve injury results in degradation of the neuromuscular junction (NMJ) and blocks neurotransmission between the pre- and postsynaptic structures, which are separated by a synaptic cleft. Matrix metalloproteinases (MMPs), enzymes that degrade and modify the extracellular matrix, play critical roles in regulating NMJ remodeling. We previously demonstrated that MMP1, MMP2, MMP3, MMP7, and MMP9 are overexpressed in facial nerve-innervated orbicularis oris muscle after facial nerve injury in a rat model. In the present study, the MMP inhibitor prinomastat was administered to rats after facial nerve injury. The MMP levels, agrin expression, and muscle-specific kinase (MuSK) phosphorylation were evaluated. Variations in evoked electromyography (EEMG) amplitude were also recorded. Compared with the control group, MMP expression in the orbicularis oris after facial nerve injury was significantly reduced in the prinomastat group. Inhibition of MMP expression maintained agrin expression and MuSK phosphorylation; the NMJ morphology was also protected after the injury. Moreover, prinomastat treatment sustained EEMG amplitude and muscle tension after the injury. These findings indicate that inhibiting MMPs can protect the function and morphology of the NMJ and demonstrate the need for protection of the NMJ at early stages after facial nerve injury.

New Technology: Compound Abnormal Muscle Response During Microvascular Decompression for Hemifacial Spasm.

OBJECTIVE: To discuss effect of intraoperative compound abnormal muscle response (AMR) in patients undergoing microvascular decompression (MVD) for hemifacial spasm (HFS). METHODS: Eighty-six HFS patients were underwent single or compound AMR monitoring during MVD. Single AMR recording was from the frontal muscle by stimulation of the marginal mandibular branch. Compound AMR recordings were obtained from the orbicularis oris and mentalis muscles by electrical stimulation of the temporal branch of the facial nerve, and from the frontal and orbicularis oculi muscles by stimulation of the marginal mandibular branch. Clinical outcome was compared with compound AMR results at the completion of MVD. RESULTS: Forty-two of 45 patients' AMR were recorded by compound AMR monitoring and 34 of 41 patients' AMR were recorded by single AMR monitoring during MVD. Hemifacial spasm resolved completely in 41 patients whose compound AMR was recorded and in 26 patients whose single AMR was recorded. Compound AMR gained a sensitivity of 96.3% and a specificity of 97.2%. Correspondingly, single AMR gained a sensitivity of 97.1% and a specificity of 86.3%. CONCLUSIONS: Our results suggest that compound AMR is more suitable than single AMR in MVD for HFS.

Sensory and motor electrophysiological mapping of the cerebellum in humans.

Cerebellar damage during posterior fossa surgery in children can lead to ataxia and risk of cerebellar mutism syndrome. Compartmentalisation of sensorimotor and cognitive functions within the cerebellum have been demonstrated in animal electrophysiology and human imaging studies. Electrophysiological monitoring was carried out under general anaesthesia to assess the limb sensorimotor representation within the human cerebellum for assessment of neurophysiological integrity to reduce the incidence of surgical morbidities. Thirteen adult and paediatric patients undergoing posterior fossa surgery were recruited. Sensory evoked field potentials were recorded in response to mapping (n = 8) to electrical stimulation of limb nerves or muscles. For motor mapping (n = 5), electrical stimulation was applied to the surface of the cerebellum and evoked EMG responses were sought in facial and limb muscles. Sensory evoked potentials were found in two patients (25%). Responses were located on the surface of the right inferior posterior cerebellum to stimulation of the right leg in one patient, and on the left inferior posterior lobe in another patient to stimulation of left forearm. No evoked EMG responses were found for the motor mapping. The present study identifies challenges with using neurophysiological methods to map functional organization within the human cerebellum and considers ways to improve success.

Forehead Movement Discrepancies After Botulinum Toxin Injections: A Review of Etiology, Correction, and Prevention.

BACKGROUND: Forehead rhytides are a popular target for botulinum toxin injections, but neuromodulation of the frontalis can be fraught with complications because of its anatomic complexity and integral role in brow position and expressivity. OBJECTIVE: This article explores common forehead movement discrepancies that can occur after neuromodulation of the frontalis, as well as how to correct and prevent them. METHODS: A review of the literature was conducted and combined with clinical experience to examine underlying forehead anatomy, etiology and correction of forehead movement discrepancies, and important factors to consider before injecting the frontalis with botulinum toxin. RESULTS AND CONCLUSION: Variable anatomy from person to person necessitates an individualized treatment approach to achieve the best cosmetic results and prevent the occurrence of forehead movement discrepancies.

Aesthetic Repair of Unilateral Cleft Lip using the Modified Inferior Triangle and Adjunctive Techniques.

SUMMARY: Surgical management of unilateral cleft lip is challenging. Correction requires a comprehensive approach to ensure optimal aesthetic outcomes. Various techniques have been proposed for the repair of cleft lip. This article and video vignette highlight the senior author's (D.S.) preferred method for repair of a unilateral cleft lip using a modified inferior triangle technique, a Noordhoff triangular flap for vermillion augmentation, orbicularis oris chemodenervation to reduce tension at the repair site, and autologous fat grafting for lip sculpting.

An anatomical appraisal of dynamic muscle transfer of the orbicularis oculi muscle.

Facial nerve palsy can cause significant distress for patients. We investigated the innervation of the orbicularis oculi muscle (OOM) and assessed the viability of unipedicle contralateral muscle transfer to restore symmetrical and spontaneous blinking. Cadaveric dissection and measurements were performed on lite fixed cadavers (n = 15). Medial innervation of the OOM was identified prior to raising and transposing a flap to the contralateral eyelid. Measurements were performed in-situ and following transposition. A medial ascending branch of the buccal nerve innervating the OOM was identified bilaterally in all cadavers. The average length of flap raised was 59.85 mm (± 4.69 mm) with no difference between the left and right. Flaps with pedicles not dissected off the bone covered 48% of the ciliary margin length (CM) and 62% of the palpebral length (PL). Flaps dissected off the bone covered 72% of the CM and 92% of the PL. The results demonstrate that a flap can theoretically transpose to >50% of the contralateral eyelid length. Increased coverage of the eyelid was achieved by releasing the pedicle from the underlying bone. Little attention was focused on buccal innervation of the eyelids, and this consistent medial pattern may allow an innervated flap transfer to restore symmetrical blinking, something that eludes modern paralysis surgery in a single-stage procedure.

Selective Facial Muscle Activation with Acute and Chronic Multichannel Cuff Electrode Implantation in a Feline Model.

OBJECTIVES: Facial paralysis is a debilitating condition with substantial functional and psychological consequences. This feline-model study evaluates whether facial muscles can be selectively activated in acute and chronic implantation of 16-channel multichannel cuff electrodes (MCE). METHODS: Two cats underwent acute terminal MCE implantation experiments, 2 underwent chronic MCE implantation in uninjured facial nerves (FN) and tested for 6 months, and 2 underwent chronic MCE implantation experiments after FN transection injury and tested for 3 months. The MCE were wrapped around the main trunk of the skeletonized FN, and data collection consisted of EMG thresholds, amplitudes, and selectivity of muscle activation. RESULTS: In acute experimentation, activation of specific channels (ie, channels 1-3 and 6-8) resulted in selective activation of orbicularis oculi, whereas activation of other channels (ie, channels 4, 5, or 8) led to selective activation of levator auris longus with higher EMG amplitudes. MCE implantation yielded stable and selective facial muscle activation EMG thresholds and amplitudes up to a 5-month period. Modest selective muscle activation was furthermore obtained after a complete transection-reapproximating nerve injury after a 3-month recovery period and implantation reoperation. Chronic implantation of MCE did not lead to fibrosis on histology. Field steering was achieved to activate distinct facial muscles by sending simultaneous subthreshold currents to multiple channels, thus theoretically protecting against nerve damage from chronic electrical stimulation. CONCLUSION: Our proof-of-concept results show the ability of an MCE, supplemented with field steering, to provide a degree of selective facial muscle stimulation in a feline model, even following nerve regeneration after FN injury. LEVEL OF EVIDENCE: N/A.

Microanatomy of the Frontal Branch of the Facial Nerve: The Role of Nerve Caliber and Axonal Capacity.

BACKGROUND: A commonly seen issue in facial palsy patients is brow ptosis caused by paralysis of the frontalis muscle powered by the frontal branch of the facial nerve. Predominantly, static methods are used for correction. Functional restoration concepts include the transfer of the deep temporal branch of the trigeminal nerve and cross-facial nerve grafts. Both techniques can neurotize the original mimic muscles in early cases or power muscle transplants in late cases. Because axonal capacity is particularly important in cross-facial nerve graft procedures, the authors investigated the microanatomical features of the frontal branch to provide the basis for its potential use and to ease intraoperative donor nerve selection. METHODS: Nerve biopsy specimens from 106 fresh-frozen cadaver facial halves were obtained. Histologic processing and digitalization were followed by nerve morphometric analysis and semiautomated axon quantification. RESULTS: The frontal branch showed a median of three fascicles (n = 100; range, one to nine fascicles). A mean axonal capacity of 1191 ± 668 axons (range, 186 to 3539 axons; n = 88) and an average cross-sectional diameter of 1.01 ± 0.26 mm (range, 0.43 to 1.74 mm; n = 67) were noted. In the linear regression model, diameter and axonal capacity demonstrated a positive relation (n = 57; r2 = 0.32; p < 0.001). Based on that equation, a nerve measuring 1 mm is expected to carry 1339 axons. CONCLUSION: The authors' analysis on the microanatomy of the frontal branch could promote clinical use of cross-facial nerve graft procedures in frontalis muscle neurotization and free muscle transplantations.