Significance of the Marginal Mandibular Branch in Relation to Facial Palsy Reconstruction

Abstract

Background The marginal mandibular branch (MMB) of the facial nerve provides lower lip symmetry apparent during human smile or crying and is mandatory for vocal phonation. In treating facial palsy patients, so far, little attention is directed at the MMB in facial reanimation surgery. However, isolated paralysis may occur congenital, in Bell's palsy or iatrogenic during surgery, prone to its anatomical course. A variety of therapies address symmetry with either weakening of the functional side or reconstruction of the paralyzed side. To further clarify the histoanatomic basis of facial reanimation procedures using nerve transfers, we conducted a human cadaver study examining macroanatomical and microanatomical features of the MMB including its axonal capacity. Methods Nerve biopsies of the MMB were available from 96 facial halves. Histological processing, digitalization, nerve morphometry investigation, and semiautomated axonal quantification were performed. Statistical analysis was conducted with P < 0.05 as level of significance. Results The main branch of 96 specimens contained an average of 3.72 fascicles 1 to 12, and the axonal capacity was 1603 ± 849 (398–5110, n = 85). Differences were found for sex (P = 0.018), not for facial sides (P = 0.687). Diameters were measured with 1130 ± 327 μm (643–2139, n = 79). A significant difference was noted between sexes (P = 0.029), not for facial sides (P = 0.512.) One millimeter in diameter corresponded to 1480 ± 630 axons (n = 71). A number of 900 axons was correlated with 0.97 mm (specificity, 90%; sensitivity, 72%). Conclusions Our morphometric results for the MMB provide basic information for further investigations, among dealing with functional reconstructive procedures such as nerve transfers, nerve grafting for direct neurotization or babysitter procedures, and neurectomies to provide ideal power and authenticity.

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

“…64 For the marginal mandibular branch, our workgroup found a mean axonal capacity of 1603 and a mean cross-sectional diameter of 1.1 mm. 16 Interestingly, although findings on axonal load and diameter were higher for the marginal mandibular branch, the cutoff to reach 900 axons was 0.97 mm, 16 which is similar to our present investigation on the frontal branch (0.94 mm). As our works are methodically identical, these findings suggest that the correlation between axonal capacity and cross-sectional nerve diameter is stable between the frontal branch and marginal mandibular branch level 1 branch.…”

“…[10][11][12][13] The microscopic features of this branch have not been investigated, whereas other branches of the facial nerve have been intensely studied. 9,[14][15][16] The present study was focused on the microanatomical aspects of the frontal branch to provide the basis for its potential use in cross-facial nerve graft procedures and offer guidance for intraoperative donor nerve capacity estimation.…”

Selective ansa cervicalis nerve transfer to the marginal mandibular nerve for lower lip reanimation: An anatomical study in cadavers and a case report

“…While this mismatch can explain the unpredictable results described above when innervating the full facial nerve with the ACN, and thus shed light on the hesitancy of plastic surgeons to adopt the technique, its use for reinnervating a single branch of the facial nerve—such as the MMN—should be consistently reliable. The MMN has an axon count of only 1603 ± 849 (Mandlik et al, 2019 ), and the nerve diameters of the ACN and MMN match, both in the literature (Chhetri & Berke, 1997 ; Loukas et al, 2007 ; Mandlik et al, 2019 ; Prades et al, 2015 ) and in the current study. The fact that the ACN has been used in the field of otorhinolaryngology for a century (Frazier, 1924 ) and remains the donor nerve of choice for the size‐wise similar laryngeal nerve (Ayyoubian & Koruji, 2011 ; Chhetri & Berke, 1997 ; Chhetri & Blumin, 2012 ; Crumley & Izdebski, 1986 ; Lee et al, 2007 ; Loukas et al, 2007 ; Olson et al, 1998 ; Prades et al, 2015 ; Wang et al, 2011 ) further strengthens its potential as a reliable selective donor nerve for the MMN.…”

“…Here, the common nerve branch to the sternothyroid and sternohyoid muscle was used primarily, but other branches are also available (Crumley & Izdebski, 1986 ; Lee et al, 2007 ; Olson et al, 1998 ; Prades et al, 2015 ). The ACN diameter, which matches the diameter of the MMN, seems to be preserved in these branches (Chhetri & Berke, 1997 ; Loukas et al, 2007 ; Mandlik et al, 2019 ; Prades et al, 2015 ). No “short ansa” variant was encountered in the clinical case.…”

“…Among the facial nerve branches, the marginal mandibular branch of the facial nerve (MMN) has often been neglected in facial reanimation (Mandlik et al, 2019 ; Terzis & Kalantarian, 2000 ), but has received increasing attention in recent years (Tzafetta et al, 2021 ). While several options for nerve reanimation exist in oncological patients (Bianchi et al, 2012 ), a regional nerve transfer procedure offers the benefits provided by a vascularized donor nerve in proximity to the recipient site and completion in a single stage.…”