[Anatomy of the marginal mandibular branch of the facial nerve]

Cadaveric Study of Topographic Anatomy of Temporal and Marginal Mandibular Branches of the Facial Nerve in Relation to Temporomandibular Joint Surgery

PURPOSE

Detailed anatomy of the facial nerve, including the variations among different ethnic groups, is essential to prevent an iatrogenic injury. The purpose of the study was to document topographic anatomy of temporal and marginal mandibular (MM) branches of the facial nerve in relation to temporomandibular joint (TMJ) surgery. The specific aim was to demonstrate detailed course of temporal and MM nerves, their surgical implications, and to compare the results obtained with the previous studies.

METHODS

The investigators implemented a prospective cadaveric study. A dissection was carried out on 52 facial halves. The facial nerve was dissected according to the instructions described in the Cunningham^'s dissection manual. Anatomic landmarks were selected as determined by Al-Kayat and Bramley, and results obtained were compared with previous published articles.

RESULTS

The study sample was composed of 52 facial halves (males, n = 35; females, n = 17). The number of branches of temporal nerve varied in dissected facial halves from 3 (n = 37 [70%]), 2 (n = 14 [26%]), to 1 (n = 1 [2%]). The distance between the lowest concavity of the bony external auditory meatus to the point at which the facial nerve bifurcates (distance B) was considerably less in the study population (1.79 cm) when compared with the reported literature (2.3 cm). There was no significant influence of gender and cephalic index on distances measured. There was 1 branch in 15% of the dissected facial halves (1 in 52) and 2 branches in 85% (44 of 52). The MM nerve was seen coursing below the inferior border of the mandible, and in 44 (85%), the nerve was present above the inferior border of mandible all along the course.

CONCLUSIONS

The topographic anatomy of the temporal and MM nerves is the same as reported in the literature. The only considerable difference was found in distance B; hence, surgical procedures involving the distance B require special consideration.

Variation of Marginal Mandibular Nerve in a Caucasian Male Cadaver: A Study Using the Anatomage Table

Anatomage (Anatomage, Inc., San Jose, CA) is a modern method for studying anatomy. It is a state-of-the-art method used for the representation of the structure of the human body. In our study, we examined the seventh cranial nerve of a male Caucasian cadaver using an Anatomage Table in the Anatomy Department of the School of Medicine, National and Kapodistrian University, Athens, Greece. After exiting the skull from the stylomastoid foramen, the facial nerve divided into the temporofacial and cervicofacial main branches. The cervicofacial branch divided into its own branches, including the marginal mandibular nerve (MMN), which ran within the investing (superficial) layer of the deep cervical fascia. We found a variation of the course of the marginal mandibular branch of the facial nerve. In the area of the lower border of the mandible, where the MMN actually crossed the facial artery and vein, it appeared to run deeper than both of those vessels, rather than running superficially. This seemed to be a rare variation of the location of the MMN relative to the facial vessels, which suggested that extra care is essential in surgical approaches within this area.

Mandibular subcondylar fracture accessibility with transparotid approach by rhytidectomy and modified Risdon approach: An anatomical comparative study

PURPOSE

The purpose of our anatomical study was to compare the accessibility of the area at the level of the neck of the condyle and the condylar head by two different approaches: the modified Risdon approach and a transparotid approach by rhytidectomy (TPAR).

METHODS

An anatomical study was performed on 12 heads of cadavers preserved with a solution rich in glycerin and ethanol, but very low in formalin. A modified Risdon approach and a TPAR were each performed on a hemiface of the same head. The bone surface was rendered digitally accessible on an anatomical diagram using Image J software. The software was used to determine a concordance score between the area of accessibility and the area of interest necessary for osteosynthesis of a high subcondylar fracture. This score was presented as a numerical scale from 0 to 100. We measured the total number of pixels in our area of interest and assigned it a score of 100. We then compared the area of accessibility with the area of interest necessary for osteosynthesis of a high subcondylar fracture.

RESULTS

Using the modified Risdon approach, an average score of 55.88 (SD = 18.96) was found, or 55.88% of the accessible area of interest. Using TPAR, we found a score of 91.05 (SD = 7.95) or 91.05% of the accessible area of interest. This difference in score between the two techniques was significantly different (p < 0.001), taking into account intra-hemiface and intra-individual correlation.

CONCLUSION

TPAR seems to be more effective in treating high condylar process fractures of the mandible.

Preserving the marginal mandibular branch of the facial nerve during submandibular region surgery: a cadaveric safety study

Background

The marginal mandibular branch of the facial nerve is vulnerable to iatrogenic injuries during surgeries involving the submandibular region. This leads to significant post-operative morbidity. Studies assessing accurate anatomical landmarks of the marginal mandibular branch are sparse in South Asian countries. Present study was conducted to assess the relationship between the marginal mandibular branch and the inferior border of the body of mandible.

Methods

Twenty-two preserved cadavers of Sri Lankan nationality were selected. Cadavers were positioned dorsal decubitus with necks in extension. The maximum perpendicular distance between the inferior/caudal most ramus of the marginal mandibular branch and the inferior border of the body of the mandible was recorded on both hemi faces.

Results

Recorded maximum distance was 17.65 mm on left side and 10.80 mm on right side. Mean maximum distance, was 7.12 ± 2.97 mm. There was no statistically significant difference in the maximum deviation on left (7.84 ± 3.41 mm) and right sides (6.44 ± 2.37 mm).

Conclusion

Course of the marginal mandibular nerve is complex. If the distance of the incision in the posterior submandibular approach is less than 2 cm from the inferior border of the mandible, there is a high probability of damaging the inferior ramus of the marginal mandibular branch of the facial nerve.

A More Favorable Lower-Lip Incision for the Removal of Deep Intraoral Malignancies

The straight midline lower lip-splitting incision has traditionally been performed with different types of deep intraoral malignancies for obtaining wide surgical access, and it can also be extended to the submandibular region or the neck to concurrently perform a neck dissection. But meanwhile, it is associated with unfavorable aesthetic and functional complications such as conspicuous facial scar, lip vermilion notching, stenosis of the labial sulcus, decreased lip sensation and movement, and oral incontinence. We designed a more favorable lower-lip incision, namely, para-lower lip incision, using the exposure and en blot resection of deep intraoral tumors. Compared with the traditional incision line, our designed line is shorter, and 20 outpatients (primary tumor site including buccal mucosa, tongue, mandibular gingiva, maxillary sinus, palate, and mouth floor) follow-ups indicated the postoperative scar is inconspicuous, no lip contour deformity and dysfunction or complications of facial paralysis such as distortion of commissure happened. This article reports one case of our patients who underwent para-lower-lip incision approach for the removal of squamous cell carcinoma (T3N2M0) in the left plate and the results of the patient were favorable.

[Anatomic study of the submental artery relationships for submental flap raising]

INTRODUCTION

Submental flap is useful for intra-oral reconstructions and reconstructions of the lower two thirds of the face. Dissection is delicate because of a difficult exposure under the lower rim of the mandible, numerous collateral arterial branches and the proximity of the marginal branch of the facial nerve. The aim of our work was to propose anatomical landmarks in order to facilitate the submental flap raising.

MATERIAL AND METHOD

Ten bodies preserved in Biomet liquid were dissected bilaterally. The anatomic relationships between the marginal branch of the facial nerve and the mandible, the relationships of the submental artery, the amount and the location of its collateral branches were measured by means of a caliper.

RESULTS

The highest marginal branch observed was located 0.5 cm above the mandibular lower rim, while the lower one was located 0.6cm below this rim. The mean length measured between the facial artery at its crossing over the mandibular rim at the level of the pre-angular notch and the origin of the submental artery was 1.5cm. The average number of collateral branches was 3.6.

DISCUSSION

A skin incision made directly under the mandibular lower rim, as mentioned by some authors, may endanger the mandibular marginal branch of the facial nerve. Three positions of the submental artery in relation to the sub-maxillary gland are reported. The collateral branches are intended for gland, muscle, skin and bone. It is necessary to pay particular attention to the sub-lingual artery, an artery of big diameter that arises at 2.8cm on average from its origin and plunges towards the mouth's floor. It must not be followed at risk of clamping the thin pedicle destined to the digastric muscle. It is important to preserve the fat tissue around the submental pedicle in order to avoid venous congestion of the flap.

Relationship between facial nerve damage and transbuccal trocar placement: an anatomical cohort study

The surgical treatment of ramus and mandibular angle fractures is typically performed by intraoral and transbuccal approaches. As these approaches may result in nerve damage, this anatomical study was performed to establish the relationship between the transbuccal trocar position and the likelihood of inducing facial nerve damage. Twenty dissections of the parotid regions were performed after a simulation of surgical approaches aimed at addressing mandibular condylar and angle fractures. Two trocar tubes, ramic and angular, were inserted and left in position throughout the dissection. This procedure allowed the qualitative relationship between the various tube positions and facial nerve damage to be analyzed. The potential risk of contact between the ramic trocar and the facial nerve branches was 90%, while the angular trocar was in contact in 45% of cases. There was no contact with the trunk, cervicofacial division, or temporofacial division of the facial nerve. The contacts occurred at the level of secondary division branches, particularly pronounced for superior and inferior buccal branches, despite the absence of macroscopically visible trauma. Based on these findings, it is proposed that trocars should be used in procedures aimed at addressing subcondylar or angle fractures of the mandible.

Intraoperative localization of the marginal mandibular nerve: a landmark study

Background

Identification and preservation of the marginal mandibular nerve (MMN) remains an important step in otolaryngology procedures. Current publications place the MMN at least 1 cm below the mandible. This study will evaluate the accuracy of the method of determining the surgical location of this branch of the facial nerve in vivo.

Methods

MMN were examined in 52 consecutive otolaryngology patients. Using a validated landmarking scheme, distances were measured from the inferior edge of the mandible and the lowest point of the nerve. A comparison of 33 nerves pairs was undertaken. Effect of patient’s age was analysed.

Results

Eighty five nerves were landmarked. The mean position of the nerve was 0.2–3.4 mm higher than the margin of the mandible. There were no significant difference in position with respect to age and left versus right comparisons.

Conclusion

The marginal mandibular nerve (MMN) is significantly higher than previously published. The location of the nerve on the right does not correlate with the left. Location of the nerve does not correlate with patient’s age.

Evaluation of clinically relevant landmarks of the marginal mandibular branch of the facial nerve: A three-dimensional study with application to avoiding facial nerve palsy

Injury to the marginal mandibular branch of the facial nerve (MMN) during surgery often results in poor functional and cosmetic outcomes. A line two finger breadths or 2 cm inferior to the border of the mandible is commonly used in planning neck incisions to avoid injury to the MMN. The purpose was to compare the two finger breadth/2 cm landmarks in predicting MMN course, and their accuracy/reliability. Thirty-one cadaveric specimens were scanned to obtain 3D surface topography (FARO® scanner). Four independent raters pinned the inferior border of the mandible and a two finger breadth line and 2cm line below. The location of each pin was digitized (Microscribe™). A preauricular flap was raised, and MMN branches were digitized and modelled (Geomagic®/Maya®) enabling quantification of the accuracy of these landmarks. The location of the two-finger breadth line was variable, spanning 25-51 mm below the inferior border of the mandible (ICC = 0.10). The most inferior MMN branch did not pass below the two-finger breadth line in any specimen, but a narrow clearance zone (≤5 mm) was found in two. In contrast, in 7/31 specimens, the most inferior MMN branch coursed below the 2 cm line and would be at risk of injury. It was concluded that an incision two finger breadths below the inferior border of the mandible could provide safer access than the 2 cm line. After an incision has been placed using the two finger-breadth landmark, caution must be exercised during dissection as branches of the MMN may lie only a few millimeters superior to the incision.

Marginal mandibular branch of the facial nerve: An anatomical study

Smile is one of the most natural and important expressions of human emotion. Man uses his lips mainly to register his emotions. Thus, the slightest asymmetry or weakness around the lips and mouth may transform this pleasant expression into embarrassment and distortion. The circumoral musculature, the major part of which is supplied by the marginal mandibular branch of the facial nerve, is the main factor in this expression. Therefore, an injury to this nerve during a surgical procedure can distort the expression of the smile as well as other facial expressions. This nerve often gets injured by surgeons in operative procedures in the submandibular region, like excision of the submandibular gland due to lack of accurate knowledge of variations in the course, branches and relations. In the present study, 50 facial halves were dissected to study the origin, entire course, termination, branches, muscles supplied by it, its anastomoses with other branches of facial nerve on the same as well as on the opposite side and its relations with the surrounding structures. The marginal mandibular branch of the facial nerve was found superficial to the facial artery and (anterior) facial vein in all the cases (100%). Thus the facial artery can be used as an important landmark in locating the marginal mandibular nerve during surgical procedures. Such a study can help in planning precise and accurate incisions and in preventing the unrecognized severance of this nerve during surgical procedures.

Is the high submandibular transmasseteric approach to the mandibular condyle safe for the inferior buccal branch?

PURPOSE

There are basically 3 main approaches for extra-articular mandibular condyle fractures: low cervical, retromandibular and preauricular. These include a risk of facial palsy affecting the marginal mandibular branch. We use a high submandibular transmasseteric approach featuring masseter section 10-20 mm above the mandibular basilar edge. Our null hypothesis was that both the marginal mandibular and the inferior buccal branches are not more at risk than in other surgical approaches.

METHODS

This study was based on 20 parotidomasseteric dissections from 10 embalmed cadaveric heads. We used as reference the vertical line, passing through the mandibular angle, parallel to the preauricular line. We performed measurements of the marginal mandibular and inferior buccal branches' heights.

RESULTS

The inferior buccal branch had an average height of 16.8 mm and the highest standard deviation (7.2). Extremes were, respectively, 32 and 7 mm. The marginal mandibular branch had an average height of 3.2 mm with standard deviation equal to 3.0. Extremes were, respectively, 9 and -3 mm.

CONCLUSION

The high submandibular transmasseteric approach provides great exposure of facial nerve branches lying on the masseter muscle, if even encountered. Through masseteric incision performed between 10 and 20 mm above the basilar edge of the mandible, the marginal mandibular branch is safe from wound with an added safety margin of 4 mm. The surgeon using this approach is most likely to encounter the inferior buccal branch. It can then be avoided under visual control. This makes it a swift and safe approach to the mandibular condyle.

Anatomosurgical study of the marginal mandibular branch of the facial nerve for submandibular surgical approach

The purpose of this study was to estimate the distance from the mandibular marginal branch of the facial nerve to the inferior margin of the mandible in order to determine the best and safest location to approach the posterior mandibular region. Forty-five hemi-faces of 27 Brazilian adult cadavers were dissected and the distance between the mandibular marginal branch and the inferior margin of the mandible was measured. The number of marginal branches and anastomoses with other branches of the facial nerve was also recorded. The evaluation of the anatomic pieces showed 1 to 3 branches of the marginal mandibular branch, anastomoses with the buccal and cervical branches of the facial nerve and distances between 1.3 cm to +1.2 cm from the inferior margin of the mandible. In 57.7% of the cases, the nerve passed superiorly and along the length of the inferior margin of the mandible. Based on the findings of the present anatomosurgical study, it may be recommended an incision 3 cm below the inferior margin of the mandible associated to a careful dissection in planes and flap retraction. This is expected to reduce the risk of neuropraxia of the marginal mandibular nerve making the submandibular incision a safe approach.

Mandibular landmarks as an aid in minimizing injury to the marginal mandibular branch: A metric and geometric anatomical study

Iatrogenic injury to the marginal mandibular branch is an important reason for medicolegal actions. The aim of this study was to determine the distance of the marginal mandibular branch to the inferior border of the mandible as well as variation of nerve position in relation to this border. The marginal mandibular branch was dissected carefully in a number of 36 facial halves. Three points were identified on the inferior border of the mandibular ramus: Point A at the angle of the mandible, Point B just anterior to the facial artery, and Point C, 2 cm anterior to Point B. A metric and geometric morphometric analysis, including thin-plate spline and relative warp analysis was done to determine the variation of nerve position in relation to these three bony landmarks. The metric study indicated a median distance from Point A to the nerve 2.3 mm inferior to Point A, 2.4 mm superior to Point B, and 10.7 mm superior to Point C. The shape analysis indicated that variation in the position of the nerve occurs most commonly at Points A and B. We conclude that these mandibular landmarks may assist surgeons in minimizing marginal mandibular branch injury and patient discomfort.