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British Journal of Oral and Maxillofacial Surgery 52 (2014) 230–235

Available online at www.sciencedirect.com

oes the great auricular nerve predict the size of the mainrunk of the facial nerve? A clinical and cadaveric study. Colbert a,∗,1, David A. Parry b,1, Beverley Hale c, James Davies d, P.A. Brennan a

Department of Oral and Maxillofacial Surgery, Queen Alexandra Hospital, Portsmouth PO6 3LY, UKGuys Campus, GKT, London SE1 1UL, UKUniversity of Chichester, College Lane, Chichester, West Sussex PO19 6PE, UKDepartment of Oral and Maxillofacial Surgery, Queen Alexandra Hospital, Cosham, Portsmouth, Hampshire PO6 3LY, UK

ccepted 2 December 2013vailable online 25 December 2013

bstract

here seems to be only individual clinical experience and some anecdotal evidence about a relation between the width of the great auricularerve (GAN) and the size of the main trunk of the facial nerve during parotidectomy. To our knowledge no anatomical studies have beenublished. In this cadaveric and clinical study we measured the widest point of the GAN as it crosses the sternomastoid muscle before it divides,nd the main trunk of the facial nerve before it bifurcates. Measurements were obtained from 16 patients who required formal superficialarotidectomies with identification of the facial nerve, and from 21 cadavers (16 formalin-fixed and 5 fresh frozen) where both sides wereissected. We recorded the results and the side of dissection. The mean (SD) width of the GAN and facial nerve from all the dissectionsas 2.75 (0.53) mm and 2.83 (0.54) mm, respectively. There was a strong correlation between the width of the nerves from both sides (left:

= 0.934, p < 0.001; right: r = 0.940, p < 0.001). The nerves did not differ significantly in size in patients or cadavers (GAN: right, p = 0.873;

eft, p = 0.486; facial nerve: right, p = 0.931; left, p = 0.691). We have found that the GAN accurately predicts the width of the main trunk ofhe facial nerve. This is particularly useful surgically as a narrow GAN can alert the surgeon to expect a small facial nerve.

2013 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

eywords: Great auricular nerve; Facial nerve; Width; Parotidectomy; Correlation; Predictor

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ntroduction

he great auricular nerve (GAN) is at risk of injury duringany procedures in the head and neck and is reported as the

erve most commonly injured in rhytidectomy.1 Its deliber-te sacrifice because of tumour involvement or to improveurgical access may be appropriate, but accidental iatrogenic

njury is undesirable and seriously affects a patient’s qualityf life.2

∗ Corresponding author. Tel.: +44 7894743416.E-mail addresses: serryth@yahoo.com (S. Colbert),

.Hale@chi.ac.uk (B. Hale), jamesdaviesradc@gmail.com (J. Davies),eter.brennan@porthosp.nhs.uk (P.A. Brennan).

1 Joint first authors.

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266-4356/$ – see front matter © 2013 The British Association of Oral and Maxillofaciahttp://dx.doi.org/10.1016/j.bjoms.2013.12.001

The GAN leaves the cervical plexus at the posterior borderf the sternocleidomastoid muscle (Erb’s point) and coursesnteriorly over the lateral surface of the muscle.3 It thenourses superiorly and divides into anterior and posteriorranches which supply sensation to the skin overlying thearotid gland and lower pole of the ear.4 Where possible,reservation of the posterior branch is recommended to retainensation to the ear and neck.5 Brown and Ord recommendedts preservation during routine parotid surgery, as it is asso-iated with less postoperative sensory morbidity.6

During many parotidectomies, when formal identificationf the main trunk of the facial nerve has been required (aspposed to extracapsular dissection), we have thought that

here might be a relation between the width of the GAN andhat of the main trunk of the facial nerve when it is sub-equently identified. This has been particularly relevant in

l Surgeons. Published by Elsevier Ltd. All rights reserved.

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S. Colbert et al. / British Journal of Oral

atients who were found to have a narrow GAN and a nar-ow facial nerve trunk. Others have reported similar findingslthough they are anecdotal.7,8

Clinical studies on the GAN have primarily focused onts injury and associated postoperative sequelae, but to ournowledge no anatomical studies have investigated whetherhere is a relation between its width and that of the main trunkf the facial nerve. Papers published to help surgeons withissection of the main trunk of the facial nerve during parotidurgery do not refer to any anatomical relation.9

We did a clinical and anatomical study to assess the rela-ion between the GAN at its widest point as it crosses theternomastoid muscle before bifurcating, and the main trunkf the facial nerve.

ethod

his was a collaborative study between the Department ofral and Maxillofacial Surgery, Queen Alexandra Hospital,ortsmouth; the Department of Histopathology at Salis-ury District Hospital; and the Department of Anatomy anduman Sciences at Guy’s Campus, Guys, King’s and Sthomas’ Medical School.

We studied 16 patients undergoing parotid surgery whoequired formal identification of the main trunk of the facialerve, and 21 cadavers (16 formalin-fixed and 5 fresh frozen)

ig. 1. Great auricular nerve (A) and facial nerve (B) measured at operationsing a rule.

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axillofacial Surgery 52 (2014) 230–235 231

n which both sides were dissected. The GAN was exposed,nd its widest point was measured as it crossed the ster-omastoid muscle using callipers in the dissection room or

small piece of cut millimetre rule in theatre (as callipersould not be sterilised). At operation, the widths of the nervesere recorded to the nearest 0.5 mm (Fig. 1A and B). In

he dissection room callipers enabled a much more accurateeasurement to the nearest 0.1 mm (Fig. 2A and B).The main trunk of the facial nerve was then identified

sing standard surgical techniques and its width was mea-ured before it bifurcated. The anatomical side and age ofhe patient or cadaver were also recorded. Statistical analysisas done with the help of IBM SPSS Statistics (version 20.0,

BM Corp).

esults

ata on 19 men and 18 women were included in the study.ixteen formal parotidectomies (7 men, 9 women) were

ncluded and both sides of 21 cadavers were dissected (42ides). The formalin-fixed group included 7 men and 9

ig. 2. Widest dimensions of the facial nerve trunk (A) and great auricularerve (B) measured with callipers.

232 S. Colbert et al. / British Journal of Oral and Maxillofacial Surgery 52 (2014) 230–235

Table 1Mean (SD) of the right and left great auricular nerves (GAN) and facial nerve (FN) for each group.

Variable Live cases Fresh frozen cadavers Formalin-fixed cadavers All cases together

Right GAN 2.8 (0.62) 2.9 (0.45) 2.8 (0.62) 2.8 (0.59)Left GAN 2.6 (0.49) 2.9 (0.40) 2.7 (0.43) 2.7 (0.45)Right FN 2.8 (0.67) 3.0 (0.55) 2.8 (0.67) 2.9 (0.64)L

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slimits of agreement to which the 95% CI were applied to reach

eft FN 2.8 (0.43) 3.0 (0.47)

The mean (SD) width of each nerve in the different groupss shown in Table 1. The fresh frozen cadavers had largerean diameters than the other groups and slightly smaller

tandard deviations, although the reduced spread is probablyecause of the small sample size.

ifferences between the live, fresh frozen, andormalin-fixed measurements

ecause of the small size of the fresh frozen cadavers, non-arametric Kruskal–Wallis tests were used to see if the widthf the nerves differed between the 3 different groups. None ofhe probabilities suggested the groups to be different (smallestifference χ2

(2) = 0.144, p = 0.931 for right facial nerve, and

argest difference χ2(2) = 1.444, p = 0.486 for left GAN).

Pearson’s product moment correlations coefficients (androbabilities) were calculated to assess association betweeniameters of the GAN and the facial nerve.

A strong positive correlation between the nerves was

ound for both left (r = 0.934; p < 0.001) and right-sidedr = 0.940; p < 0.001) dissections (Figs. 3 and 4).

Regression analysis showed that 95% of the variationn diameter of the facial nerve could be explained from

ttG

Fig. 3. Correlation between great auricular nerve and fa

2.8 (0.40) 2.8 (0.42)

easurement of the GAN. The models (Table 2) provide val-es for each side separately, and mean measurements fromoth sides where these were available. Although the modelsere generated over a small sample, the confidence intervals

CIs) for the coefficients are small and show consistency.imilarly, the fit statistics (R2 adjusted R2 and the standardrrors of estimates) are indicative of a good fit to the data.hese results confirm that the experiential and anecdotal rela-

ions observed between dimensions of the GAN and the facialerve are supported by measurement and analysis.

We did additional analysis of the limits of agreementetween the GAN and the facial nerve to explore the extentf the differences found. This was conducted using Microsoftxcel (2010). The small sample numbers make these statis-

ics descriptive of agreement in the particular sample group.he analysis matched the structure of regression analysis andas done for the left and right sides separately, and as a meanf the 2 values.

Table 3 shows the extent of bias and 95% CI for the 3 analy-es. Figs. 5–7 provide Bland and Altman plots of the absolute

he values in the table. Our results show that a bandwidth forhe 95% CI of limits is small, and indicate that we expect theAN to be very similar to the facial nerve.

cial nerve for the left side (r = 0.934; p < 0.001).

S. Colbert et al. / British Journal of Oral and Maxillofacial Surgery 52 (2014) 230–235 233

Fig. 4. Correlation between the great auricular nerve and facial nerve for the right side (r = 0.940; p < 0.001).

Fig. 5. Bland and Altman plot of absolute limits of agreement between the great auricular nerve (GAN) and facial nerve (FN) for the left side only.

Fig. 6. Bland and Altman plot of absolute limits of agreement between the great auricular nerve (GAN) and facial nerve (FN) for the right side only.

234 S. Colbert et al. / British Journal of Oral and Maxillofacial Surgery 52 (2014) 230–235

Fig. 7. Bland and Altman plot of absolute limits of agreement between the mean great auricular nerve (GAN) and mean facial nerve (FN). Data include thosefor which left and right measures were available.

Table 2Regression models and fit statistics to predict facial nerve measurements from the great auricular nerves (GAN). Dependent variables for the models are thefacial nerve measurements (right, left, and then mean).

Variable Optimum right side model coefficients Optimum left side model Optimum mean model

GAN (R) 1.021 (0.013) – –GAN (L) – 1.034 (0.010) –Mean GAN – – 1.033 (0.012)95% CI for coefficient 0.994–1.047 0.762–0.909 1.007–1.058R2/adjusted R2 0.995/0.994

Standard error of estimate 0.2183

Table 395% CI for limits of agreement between great auricular nerve (GAN) andfacial nerve (FN).

Bias 95% lowerlimit

95% upperlimit

Left side (n = 32) −0.1 −0.4 0.2Right side (n = 35) −0.1 −0.5 0.4Mean of both sides (n = 30) −0.1 −0.5 0.3

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iscussion

ur results show a strong correlation between the width ofhe GAN as it crosses the sternomastoid before bifurcatingnd the width of the facial nerve. Therefore, during formalarotidectomy, a narrow GAN will predict a narrow facialerve trunk. Other novel techniques can be considered tonsure the safe identification of the facial nerve in additiono standard methods.8

The GAN originates from the cervical plexus at levels C2nd C3 and innervates the skin overlying the parotid gland,xternal ear, and posterior auricular region.9 It has no motoromponent although we have previously found an anatomicalariant when it communicated with the marginal mandibularranch of the facial nerve.10,11 Other communications with

he facial nerve and sensory branches of the trigeminal nervere well reported. N

0.997/0.997 0.996/0.9960.1579 0.1907

Our results did not provide any statistical evidence to sup-ort the theory that in the formalin-fixed cadavers, the widthf the GAN and facial nerve would be significantly smallerhan in fresh frozen cadavers or patients. Although widths inhe fresh frozen cadavers were slightly larger than the otherroups, given the small size of this group and the spread ofhe data, no reliable conclusion can be reached.

Shrinkage of tissue during processing is a source of contro-ersy. Kerns et al.12 reported that tissue shrinkage is primarilyaused by intrinsic tissue contractility rather than fixation inormalin. On the other hand, Chen et al.13 reported significanthrinkage of head and neck cancer specimens after fixation inormalin. Interestingly, our results failed to show that storingadavers in formalin is associated with a significant reduc-ion in the dimension of both the nerves studied; perhaps it isecause nerves are more resilient to the fixation process thanther tissues.

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