Distribution, Scaling, and Depiction of the Temporal Branches of the Facial Nerve

doi:10.21203/rs.3.rs-4868966/v1

Purpose. Iatrogenic injury to the temporal branches of the facial nerve (CN VII) is the leading postoperative complication of the preauricular surgical approach to the temporomandibular joint (TMJ). Many of the anatomical illustrations vary greatly in how the anatomy of the temporal branches of the facial nerve are depicted. Additionally, there are few studies that discuss this variation. This study aims to provide more accurate data on this discrepancy.

Methods. Here, the distribution of temporal branches of the facial nerve was examined in 20 cadaveric donors. A count of branches and the location of each was mapped as they crossed the zygomatic arch, with attention paid to variation in the breadth of the nerve free “preauricular window” which is pertinent to the surgical access to the TMJ. Comparable measures were collected from published anatomical illustrations and tested for accuracy.

Results. Preauricular window breadth measurements were found to be comparable to previous studies, but the mean value was lower here. Patterns in the nerve distribution fit a proportional model whereby the zygomatic length (ZL) is divided into five equal segments, the most posterior of which was found to be free of CN VII branches in all donors. In anatomic illustrations, the number of nerve branches crossing ZL was undercounted and the breadth of the preauricular window was overestimated.

Conclusion. Results suggest that controlling for face size could reduce the variation observed in the breadth of the facial nerve-free zone near the TMJ. Non-cadaveric reference illustrations do not represent the anatomy accurately.

Facial Nerve

Facial Nerve Injuries

Temporomandibular Joint

Medical Education

Medical Illustration

The preauricular approach and modifications to this procedure are standards for open surgery of the temporomandibular joint (TMJ)¹ and variably also used for total joint placement (TJR)¹ and fractures to the condyle and nearby regions of the mandible^2,3. Iatrogenic facial nerve injury, usually temporary, is the most common complication of this approach, affecting the functions of the frontalis and orbicularis oculi muscles. The incidence of postoperative nerve damage varies remarkably from one study to another, and while some efforts have been made to assess the relative risks of alternative approaches,^2,4 wide disparities are reported even from studies using the same approach or modifications thereof, e.g., 0–28% (mean = 14.8%; n = 6 studies) in one metanalysis², but up to 71% (n = 47) in another.⁵ Descriptions of modifications to the preauricular approach are common in the literature, but large-scale systematic reviews of the risks and benefits of these variations are uncommon, likely in part due to the tendency of these to lack sufficient anatomical detail to permit comparison. ^6,7 On the other hand, experience of the surgeon and working conditions likely effects the rate of complications,² and systematic reviews would be hard-pressed to control for these factors.

Permanent facial nerve damage affects only a minority of total patients. The commonly used benchmark of six months is significant because reinnervation via surgical repair of damaged nerves is less likely to restore function ≥ 6 months post-injury,⁸ so timely attention to any postoperative deficits is crucial and prevention should be top of mind. Careful surgical planning is a critical step in preventing TMJ surgery complication,¹ and here we consider the resources that surgeons and students have for researching and planning facial surgeries such as the preauricular approach. Anatomical studies of clinically significant nerve topology and location have been a regular point of reference in texts that describe surgical approaches to the mandible, but inconsistencies in some results or other factors limiting application in the surgical arena warrant review. Cadaveric studies providing guiding measurements and anatomical illustrations in various textbooks are available for the reference.

Al-Kayat and Brambley (1979)⁹ is a foundational reference. These authors measured the distance between the external auditory meatus (EAM) and nearby structures of the facial nerve in 28 cadaveric donors (56 facial halves) to inform the preauricular approach to accessing the TMJ. One of these measurements, here termed the “preauricular window,” is the horizontal distance between the anterosuperior brim of the EAM to the most posterior temporal branch of the facial nerve where it crosses the zygomatic arch. Knowledge of this window is of practical importance to those employing the preauricular surgical approach as it provides a prediction of the distance between a palpable bony landmark, the EAM, and the branch of facial nerve that is most immediately vulnerable to incision or stretching during the preauricular approach. Versions of this measure have been collected in three studies since. Miloro et al. (2007)¹⁰ measured the distance between the EAM and the most posterior temporal branch in MR images of 30 living patients and found a larger window than reported in the earlier study.⁹ Campero et al. (2009)¹¹ assessed the window using four partially dissected cadaveric donors, whereby they used the anterior border of the tragus rather than the margin of the EAM. Jose et al. (2021)¹² closely followed the measurement lead by Al-Kayat and Brambley (1979)⁹ in dissections of 52 facial halves of cadavers, though, they did not report the number of cadaveric subjects examined. The minimum breadth of the preauricular window varies within each of these four studies, as do the means, range, and standard deviation, when reported. Potential sources of this variation have not been explored. It is not known, for example, to what extent this measure differs from side to side in a single individual, as intrasubject differences were not reported. Nor is it known whether the size of the patient affects the proportional space between measured features, though this would affect the applicability of a guiding measurement.

A more abundant reference for reviewing the distribution of facial nerve branches across the face is the anatomical literature. Anatomical illustrations inform students at all levels of clinical education and research by adorning the pages of textbooks, atlases, anatomical reference software and specialized surgical texts. However, the cadaver lab is lauded by anatomy faculty for its ability to challenge the expectations of students, defying reference texts with variations of all sorts. Still, one might expect that professional illustrations would follow a kind of predictable pattern whereby they reflect the most common pattern in support of a foundational knowledge of every region of the body, but the extent to which this expectation is correct for the facial nerve has not been formally tested.

The aim of this study is to improve upon the reference information available to surgeons, educators and learners. We accomplish this aim by adding to what is known about the locations of the temporal branches of the facial nerve, and then by assessing the quality of currently available references that represent this anatomy graphically in support of education. First, we dissected 20 cadaveric subjects and examined the number and distribution of the temporal branches of the facial nerve as they cross the zygomatic arch in each individual. Second, we surveyed anatomical illustrations in medical student textbooks, print and digital anatomical atlases, and specialized oral and maxillofacial surgery texts for imagery of the structures examined via cadaveric dissection. Finally, we compare anatomical illustrations with cadaveric findings to assess accuracy reference images of A) the proportional breadth of the preauricular window; B) the number of CNVII branches crossing the zygomatic arch; and C) the distribution of branches across the defined region.

Cadaveric Dissections

Cadaveric dissection and data collection was done at the College of Medicine at Central Michigan University. Human cadaveric donors were loaned by the University of Toledo to the CMU College of Medicine and College of Health Professions during the 2022–2023 academic year. Permission to conduct and describe research performed on these donors, as an ancillary to their use for medical education, was granted by the Anatomy Lab Supervisor at CMU. The CMU Institutional Review Board (IRB) was consulted prior to the initiation of the research described here, and it was their determination that, on the grounds that the research involves cadavers and not living subjects, this work does not meet the definition of human subject research under the purview of the IRB according to federal regulations.

Targeted dissections of the extracranial origin and circum-parotid distribution of peripheral branches of the facial nerve were performed on 20 cadaveric donors. Though both sides were dissected in several cases, only one side of each cadaver was used for the present study to avoid confounding the data with yet-unexplored effects of intrasubject variability. Palpable bony landmarks near the preauricular surgical field and the course of the vulnerable branches were identified and used as a framework to map the distribution of facial nerve branches crossing the zygomatic arch. The region of interest defined here spans the horizontal space across the zygomatic arch between the anterosuperior apex of the external auditory meatus (EAM) and the apex of the curvature of the most inferior portion of the zygomatic bone (ZTS). These surface landmarks were palpated prior to dissection and pinned through all layers of tissue through the periosteum to retain points for reference to map the distribution of subsequently dissected nerve branches.

During dissection, the layers of skin, subcutaneous fat and superficial musculoaponeurotic system (SMAS) were examined and noted. Once the temporal branches of CN VII were identified leaving the parotid gland, they were dissected from surrounding fascia and followed across the zygomatic arch. The point at which each neural branch crossed the inferior border of the zygomatic arch between the two surface landmarks was pinned for measurement. Pictures with a ruler for scale were taken and organized in Microsoft PowerPoint slides. Each slide included a cropped image of the dissection with scale, and reference measurement lines and markers were added to demarcate the lines where measurements would be taken to standardize and record this process. Exported image files of these slides were uploaded to the image processing software, FIJI. In the program, the ruler was used to create a pixel scale for each image and measurements were taken, following the standardized reference guides, between the pinned surface landmarks and each pinned branch of the facial nerve as they crossed the zygomatic arch. Measurements between the EAM and ZTS were used as a reference for the full breadth of the field of interest, i.e., the zygomatic length (ZL). The number of facial nerve branches crossing this field was recorded and the distance from the EAM to each branch was measured and recorded. The raw measurements for the distance between the EAM and the most posterior branch of CN VII was regressed against ZL to assess the correlation of this measure of facial size and the anteroposterior length of the “preauricular window.” Finally, the distances between the EAM and each nerve crossing the defined field were transformed to a proportion of the respective donor’s ZL to control for size and facilitate comparison with anatomical illustrations.

Anatomical Illustrations

Anatomical illustrations were surveyed for non-photographic depictions of the relevant anatomy whereby each image met the following criteria: 1) subject was depicted in profile view, 2) temporal branches of the facial nerve were included, 3) bony landmarks EAM and anterior portion of the zygomatic arch were themselves depicted or associated structures were visible that provided suitable reference. For comparison with the dissection results, 20 unique images were sought. Unattributed replicates with little or no modification are commonplace in anatomical reference literature, so finding 20 unique images required a survey of three sets of reference collections: 1) the Central Michigan University College of Medicine anatomy lab, 2) the anatomy lab of the Oklahoma State University Center for Health Sciences, and 3) the personal libraries of the OSU-CHS anatomy faculty. The texts reviewed included clinical anatomy textbooks, dissection lab manuals, atlases, one anatomy reference computer program, and specialized texts produced for oral and maxillofacial surgeons. The twenty unique anatomical illustrations were digitized and organized into Microsoft PowerPoint slides following the same protocol as the images of cadaveric dissections. Measurements of nerves and landmarks were conducted in Fiji, as they were for the dissection images, except that the images of the anatomical illustrations did not have associated scales and so only proportional distances were recorded (i.e., ZL = 1).

Statistical analyses were conducted in SPSS (IBM SPSS Statistics v. 29.0.0.0-241). Non-parametric Mann-Whitney tests were used to compare dissection and illustration data because it could not be assumed that illustration data would be normally distributed.

Dissection Data

Cadaveric donor dissections (N = 20) identified an average of 4.2 facial nerve branches crossing the defined field, ZL (3-6; SD = 0.98) (Table 1). The mean distance between the EAM and the most posterior temporal branch of CN VII that crosses the zygomatic arch is 1.58 cm (0.93-2.89; SD = 0.531; Table1,2). The breadth of the preauricular window (EAM to most posterior CNVII crossing) is indeed correlated with ZL (our proxy for face size) (Table 1: r² = 0.22; p<0.001). By comparison of the coefficient of variation (CV) in the raw measurements and those scaled by face size (i.e., “EAM – Br 1” measurement divided by ZL for each individual), we find that raw measurement CV (32.84) is 16% greater than scaled values (28.22). Using proportional distances for these measures from the cadaveric dissections removes the effect of size, clarifies patterns, and allows for comparison with the anatomical illustration data. The average proportional distance between the EAM and the most posterior branch of the facial nerve identified in dissection is 0.34 (34% of the field, ZL) (0.22-0.54; SD = 0.09).

The minimum proportional distance of the closest branch to the EAM found in dissection is just over a fifth (22%) of the breadth of the defined field (ZL). Using the span of the nerve free zone as a baseline for further divisions, the contents of each fifth was then assessed (Figure 1). The most posterior CN VII branch was identified in the second division (fifth) in 13 (65%) of the dissections, with the remaining 7 exhibiting the most posterior crossing in the third division (Table 3A). On average, about one nerve branch was identified in each of the anterior four divisions (Median = 1; Mode = 1; Figure 1; Table 4A).

Comparison with Anatomical Illustrations

Anatomical illustrations (N = 20) depicted an average of 2.6 branches crossing the defined field (1-4; SD = 1.19; Table 3B, 4B). Thus, anatomical illustrations underrepresent the true density of facial nerve branches in this region when compared with the dissection results (Mann-Whitney U = 65; p<0.001).

Only proportional measurements are possible with the anatomical illustrations due to their lacking a scale for reference (Table 3B). The average proportional distance between the EAM and the most posterior branch of the facial nerve in the illustrations is 0.5 (50% of the field) (0.13-0.97; SD = 0.21). Thus, anatomical illustrations overestimate the proportional breadth of the “preauricular window” when compared with cadaveric dissections (Mann-Whitney U = 315.5; p = 0.002). Additionally, the variation in the illustration sample was markedly higher than that in the dissection sample; CV in the illustration sample for the proportional distance between EAM and the most posterior facial nerve branch (42.03) is 48.95% higher than the dissection results (28.22).

Unlike the dissection data, two of the illustrations depicted a nerve crossing in the first division (fifth) of the defined field (mean proportional distance = 0.1; 0-1; SD = 0.3; Table 3B, 4B). The average number of nerves depicted in the illustrations is about half of those identified in the dissections, and their distribution, frequently absent in 3-4 divisions, contrasts remarkably with the tendency of the dissection data wherein the median and mode of nerve crossings is one nerve in each of the anterior four divisions (Table 4; Figure 1).

Anatomical references are key in the education of future physicians, anatomists and educators. Additionally, surgical planning to avoid sensitive anatomical structures that are not visible prior to incision is standard practice, but the reference information used for this planning phase may vary depending on the experience and resources of each surgeon. Anatomical illustrations and descriptions from primary literate as well as textbooks, atlases, and specialized surgical books are all reference materials available to most, but they are not equally representative of the true anatomy. Comparison of these references with human subjects is important to verify their accuracy as they are standards for building knowledge of human anatomy. Additionally, data in the primary literature that examined the facial-nerve-free preauricular window (i.e., Table 2), includes unexplained variation in critical guiding measurements that may be artifacts of controllable factors, e.g., the effect of face size, and potential effects of intrasubject variability resulting from pooling unilateral and bilateral dissection data.

Noting unexplained variability in previously published measurements, the present study controls for two potentially confounding sources. The potential for intrasubject variability was avoided by measuring only unilateral dissections rather than measuring both sides in some donors. The influence of size, on the other hand, cannot be avoided with a natural sample. Body size is undoubtedly a prevalent source of variation in the literature, especially when considering biometric data has been reported across time and from different populations, but the present study was the first to report this in the distribution of temporal branches of the facial nerve. The effect of face size on nerve distribution measurements was tested here by using a linear proxy (ZL) and a statistically significant relationship was verified. The results of the present study, with respect to the range of measurements for the nerve-free preauricular zone, closely approximate those of the findings of previous dissection-based research with comparable sample size, i.e., Al-Kayat and Bramley (1979)⁹ and Jose et al., (2021).¹² However, the present results report a mean value that is lower than the previous research (Table 2). Having confirmed that face size can affect this measurement, it may be presumed that differences in these data is a consequence of differently sized subjects in the samples measured, though we cannot presently discount the possibility that intraindividual variation also affected the values of those studies where multiple “halves” were measured in those other studies.

A practical preoperative approach to controlling for size is to use proportional, rather than absolute measurements to map predictions of vulnerable nerve branch locations. The present study uses palpable bony landmarks to define the expanse of the zygomatic arch. The contents of five equal divisions within this space illustrate the pattern reported here. From posterior to anterior, the first division was found to be free of facial nerve branches in all 20 dissections (Table 3A,4A); the average breadth of the preauricular window was 34% of the measured zygomatic length from the EAM. Each division anterior of the first was found to contain, on average, one branch of the facial nerve for a total of one nerve each for the anterior four of the five divisions (Table 4A). Laid out in this fashion, the pattern identified from the dissection data is remarkably simple and easy to visualize. It is surprising, then, to find that the anatomical illustrations gleaned from many of the most common anatomical references, and specialty texts as well, deviate starkly from the true anatomy.

Beginning with the count of CN VII nerve branches crossing the zygomatic arch, the mean value from the anatomical illustrations (2.6) was just over half of the mean number identified in dissections (4.2). The preauricular window depicted in the illustrations differed from that found in the dissection data such that the minimum breadth of this facial-nerve-free zone was narrower in two images (13-14% of ZL in illustrations vs. 22% in dissections), while the average distance was significantly wider in the illustrations (50%) than the mean measured from dissections (34%) (Table 3). Put another way, 70% of the illustrations depict a proportionally broader preauricular window than was found in 75% of the cadaveric dissections. Taken together, these results indicate that anatomical illustrations are not satisfactory references to the true anatomy of the facial nerve in this region, instead underrepresenting the number of temporal branches while also overrepresenting the space within which a surgeon can safely operate. The illustrations studied for this comparison were gleaned from the medical education literature, including commonly used atlases and textbooks that adorn the shelves of reference libraries as well as the personal collections of many anatomists and clinicians, and these also include specialized references made by and for oral and maxillofacial surgeons. Takeaways from this comparison should inform both surgeons and medical educators, and among the lessons for the latter is that the informational value of the cadaver lab remains unmatched.

High-quality reference measurements surrounding the distribution, scaling and depiction of the branches of CNVII are rare. This study addressed variation in previously described facial nerve branch locations and adds to this limited bank of resources to better-inform surgeons and researchers with the goal of reducing iatrogenic injury to the facial nerve. Measurements from a mixed-size sample of adult cadaveric donors demonstrates that face size influences the breadth of the preauricular window, but by using a proportional approach described here, preoperative predictions of the distribution of temporal branches near the TMJ would mitigate the confounding effect of face size. Indeed, size should be accounted for in all morphometric research and reporting of surgical anatomy, or risk adopting guiding measurements that may fit one population but not another. Cadaveric dissection is time consuming and cadaver labs are not universally available, so trusted alternative references are important assets for research and anatomical education. Our survey of anatomical illustrations available from the most common textbooks, atlases, and specialized oral and maxillofacial surgery texts found distressingly inaccurate depictions of the temporal branches of the facial nerve. Altogether, the findings described here contribute to the anatomical and surgical communities’ limited resources for planning procedures and educating learners to the variations of CNVII, while also flagging the hazard of widespread inaccuracies in non-cadaveric references depicting the temporal branches of CN VII.

Author Contribution

Author B.H. and Z.K. wrote the main manuscript and created the tables. Author S.J. created the illustration for figure 1. All authors reviewed the manuscript.

Acknowledgement

The authors are extremely grateful for the generosity of the 20 cadaveric donors and their families, whose gift provided the opportunity for the education and research that led to this project. We also thank Elizabeth Dalzell and the University of Toledo for facilitating access. Central Michigan University College of Medicine (CMED) anatomy lab coordinators Dr. Jennifer Kennedy and Jacob Paige were extremely helpful in their supporting roles for the education and research at the CMU College of Health Professionals and CMED. BH received internal financial support to engage in this project courtesy of the 2022 CMED Summer Scholars Program.

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Table 1. Measurements (mm) from cadaveric dissections.

Dissection	ZL (mm)	EAM – Br 1	EAM – Br 2	EAM – Br 3	EAM – Br 4	EAM – Br 5	EAM – Br 6
D. 01	48.548	22.152	24.704	31.279	41.052
D. 02	54.34	14.669	20.779	30.399	38.521
D. 03	56.207	19.996	24.93	37.4	45.322
D. 04	50.074	10.953	19.883	24.086	27.659	36.286	44.806
D. 05	57.096	28.953	32.265	41.404	47.364	51.146
D. 06	39.548	9.29	12.939	26.559	39.548
D. 07	58.242	14.439	26.065	33.709	44.193	58.242
D. 08	53.731	23.448	28.492	31.933	37.571	40.118	47.878
D. 09	56.849	18.946	25.168	28.678	32.011
D. 10	47.232	11.084	15.487	20.618	26.966	32.981	38.789
D. 11	57.954	14.351	34.41	42.114
D. 12	46.012	18.196	24.181	30.213	38.302	46.263
D. 13	29.55	16.019	19.878	26.849
D. 14	45.203	11.735	25.69	40.158	44.129
D. 15	32.019	9.462	16.816	25.896	30.419
D. 16	37.382	12.061	18.997	25.227	34.96
D. 17	42.632	11.791	24.672	39.009
D. 18	43.745	13.105	14.703	17.336	29.799
D. 19	39.984	12.923	24.689	28.444
D. 20	48.917	21.763	33.851	44.877

ZL = Zygomatic Length as defined here; EAM = external auditory meatus; Br (#) = CNVII branch crossing zygomatic arch within ZL. Empty cells indicate that no N^th branch was detected.

Table 2. Comparison of present results to comparable past research.

Study	N		Method	EAM to most posterior CNVII branch crossing zygomatic arch
Study	people	Halves*	Method	Range (cm)	Mean (SD)
Al-Kayat and Bramley (1979)	28	56	Dissection	0.8 – 3.5	2.0 (0.5)
Miloro et al. (2007)	30		Radiograph	1.68 – 2.49	2.12 (0.21)
Campero et al. (2009)	4	8	Semi-Dissection	1.59 – 2.51	1.865
Jose et al. (2021)	?	52	Dissection	1.0 – 3.2	1.95 (0.54)
Present study	20		Dissection	0.93 – 2.89	1.58 (0.531)

*“Halves” indicated where more than one per individual was included in the study.

Table 3. Proportional distance of CNVII branches from EAM within defined field,* A) cadaveric dissections, and B) published anatomical illustrations.

A. Dissections	Br 1	Br 2	Br 3	Br 4	Br 5	Br 6
D. 01	0.46	0.51	0.64	0.85
D. 02	0.27	0.38	0.56	0.71
D. 03	0.36	0.44	0.67	0.81
D. 04	0.22	0.40	0.48	0.55	0.72	0.89
D. 05	0.51	0.57	0.73	0.83	0.90
D. 06	0.23	0.33	0.67	1.00
D. 07	0.25	0.45	0.58	0.76	1.00
D. 08	0.44	0.53	0.59	0.70	0.75	0.89
D. 09	0.33	0.44	0.50	0.56
D. 10	0.23	0.33	0.44	0.57	0.70	0.82
D. 11	0.25	0.59	0.73
D. 12	0.40	0.53	0.66	0.83	1.00
D. 13	0.54	0.67	0.91
D. 14	0.26	0.57	0.89	0.98
D. 15	0.30	0.53	0.81	0.95
D. 16	0.32	0.51	0.67	0.94
D. 17	0.28	0.58	0.92
D. 18	0.30	0.34	0.40	0.68
D. 19	0.32	0.62	0.71
D. 20	0.44	0.69	0.92

B. Illustrations	Br 1	Br 2	Br 3	Br 4	Br 5	Illustration Source
A.I. 01	0.47					Fig. 48, Berkovitz and Moxham (1988)¹³
A.I. 02	0.46	0.82	0.99			Fig. 12.2, Ellis and Zide (2018)¹⁴
A.I. 03	0.39	0.435	0.509	0.556	0.616	Fig. 39.10C, Gilroy and MacPherson (2016)¹⁵
A.I. 04	0.384	0.493	0.557	0.616	0.729	Fig. 19.9, Gilroy (2013)¹⁶
A.I. 05	0.754	0.898	0.951	0.993		Pg. 458, Drake et al. (2008)¹⁷
A.I. 06	0.966					Table 15.7, McKinley and O’Loughlin (2006)¹⁸
A.I. 07	0.568	0.691				Fig. 7.16B, Moore et al. (2014)¹⁹
A.I. 08	0.411	0.649				Plate 54, Netter (2019)²⁰
A.I. 09	0.512	0.717	0.988			Fig. 3.1, Quinn (1998)²¹
A.I 10	0.604	0.982				Fig. 3.2, Quinn and Grandquist (2015)²²
A.I. 11	0.137	0.208	0.446	0.748		Fig. 30-17, Slaby et al. (1994)²³
A.I. 12	0.497	0.978				Fig. 7-28, Snell (1978)²⁴
A.I. 13	0.35	0.416				Fig. 12.8, Van De Graaf (1997)²⁵
A.I. 14	0.56	0.638				Fig. 7.25, Detton (2017)²⁶
A.I. 15	0.441	0.651				Fig. 7.25A, Tank (2009)²⁷
A.I. 16	0.962					3D4Medical (2024)²⁸
A.I. 17	0.543					Fig. 21.3, Miloro and Kolokythas (2019)²⁹
A.I. 18	0.55	0.855	0.913	0.975		Fig. 5-6, Morris (2016)³⁰
A.I. 19	0.133	0.475	0.719			Fig. 110-1A, Dean et al. (2016)³¹
A.I. 20	0.309	0.518	0.965			Fig. 129-5, Erickson and Zuniga (2016)³²

*”Defined field” is the zygomatic length, described in text. Proportional distances are from EAM to numbered nerve branches (Br #). Empty cells indicate that no N^th branch was detected.

Table 4. Count of nerve branches identified during dissections (A), or depicted in anatomical illustrations (B), in 5 equal divisions.*

A. Dissections	Div 1	Div 2	Div 3	Div 4	Div 5
D. 01	0	0	2	1	1
D. 02	0	2	1	1	0
D. 03	0	1	1	1	1
D. 04	0	2	2	1	1
D. 05	0	0	2	1	2
D. 06	0	2	0	1	0
D. 07	0	1	2	1	1
D. 08	0	0	3	3	1
D. 09	0	1	3	0	0
D. 10	0	2	2	1	1
D. 11	0	1	1	1	0
D. 12	0	1	1	1	2
D. 13	0	0	1	1	1
D. 14	0	1	1	0	2
D. 15	0	1	1	0	2
D. 16	0	1	1	1	1
D. 17	0	1	1	0	1
D. 18	0	3	0	1	0
D. 19	0	1	0	2	0
D. 20	0	0	1	1	1
Mean (SD)	0(0)	1.05 (0.8)	1.3(0.84)	0.95(0.67)	0.9(0.7)

B. Illustrations	Div 1	Div 2	Div 3	Div 4	Div 5
A.I. 01	0	0	1	0	0
A.I. 02	0	0	1	0	2
A.I. 03	0	1	3	1	0
A.I. 04	0	1	2	2	0
A.I. 05	0	0	0	1	3
A.I. 06	0	0	0	0	1
A.I. 07	0	0	0	2	0
A.I. 08	0	0	1	1	0
A.I. 09	0	0	1	1	1
A.I 10	0	0	0	1	1
A.I. 11	1	1	1	1	0
A.I. 12	0	0	1	0	1
A.I. 13	0	1	1	0	0
A.I. 14	0	0	1	1	0
A.I. 15	0	0	1	1	0
A.I. 16	0	0	0	0	1
A.I. 17	0	0	1	0	0
A.I. 18	0	0	1	0	3
A.I. 19	1	0	1	0	1
A.I. 20	0	1	1	0	1
Mean (SD)	0.1(0.3)	0.25 (0.43)	0.9(0.7)	0.6(0.66)	0.75(0.94)

*Divisions are counted from posterior (Division 1) to anterior (Division 5) within the defined expanse (ZL).

No competing interests reported.

Distribution, Scaling, and Depiction of the Temporal Branches of the Facial Nerve

Status:

Version 1

Abstract

Figures

INTRODUCTION

MATERIALS AND METHODS

Cadaveric Dissections

Anatomical Illustrations

RESULTS

DISCUSSION

CONCLUSION

Declarations

Author Contribution

Acknowledgement

References

Tables

Additional Declarations

Status:

Version 1