European Annals of Otorhinolaryngology, Head and Neck diseases (2012) 129, 214—219

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TECHNICAL NOTE

Facial nerve identification during parotidectomy

∗

C.-A. Righini

Clinique universitaire ORL, pôle TCCR, hôpital Albert-Michallon, boulevard de la chantourne, BP 217, 38043 Grenoble cedex,

France

Introduction rior cervical regions. A larger portion of the hemiface can

be exposed by extending the anterior limits of the drapes

to the labial commissure and lateral canthus to allow visu-

Any surgical procedure involving the parotid gland requires

alization of muscle movements during dissection. A piece

precise identification of the facial nerve (cranial nerve VII).

of compress is placed in the external auditory canal to pre-

When no previous surgery has been performed on the parotid

vent accumulation of blood in the canal. The surgeon stands

gland and parotid region, the facial nerve is identified at its

on the operated side, the assistant stands on the opposite

third segment, as it leaves the stylomastoid foramen (SMF).

side. The scrub nurse preferably stands opposite the sur-

This segment of the nerve is also called the facial nerve

geon, next to the assistant, which allows the surgeon to work

trunk. A good knowledge of the anatomical landmarks of the

more freely in the parotid region but also to avoid errors of

facial nerve in the SMF is essential in order to identify the

aseptic technique.

nerve before it enters the parotid gland. After identifying

the trunk, the nerve is then dissected posteroanteriorly in

anterograde fashion. This is the most widely used method of

identification and dissection of the facial nerve [1].

Instrumentation

Patient positioning and instrumentation

No specific instrumentation is required. Bipolar cautery with

Patient positioning irrigation (either integrated in the cautery, or ensured by

a catheter placed on a syringe manipulated by the assis-

The patient is placed in the supine position on the operating tant) is used to ensure to haemostasis of vessels close to

table and with slight Trendelenburg tilting of the table. The the facial nerve while avoiding injury to the nerve. Dissec-

head is placed on a silicone gel head rest in slight hyper- tion is facilitated by using magnifying glasses. Facial nerve

extension and turned to the side opposite to the side to be monitoring is not systematically used in first-line surgery.

operated. A block is not placed underneath the shoulders However, the position of the facial nerve trunk may be modi-

unless cervical lymph node dissection is planned. Shaving of fied by the tumour: a very large tumour of the superficial

the sideburns and around the ear is not essential, as the hair lobe can displace the facial nerve more deeply, against the

can be retracted by using adhesive strips at the periphery base of the styloid process; in contrast, a tumour of the

of the field. However, the beard must be shaved in men. deep lobe can push the nerve trunk against the anterior

Surgical drapes expose the temporo-zygomatic region, the border of the mastoid process. The anatomical landmarks

ear and the preauricular region, and the malar and supe- described below are particularly valuable in these settings.

However, in these difficult cases, neurostimulation may be

useful to facilitate the surgical procedure, due to modifica-

∗

Corresponding author. tion of the anatomical course of the facial nerve trunk and

E-mail address:

[email protected] branches.

1879-7296/$ – see front matter © 2012 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.anorl.2011.12.002

Facial nerve identification during parotidectomy 215

Operative procedure The plane of dissection is selected as a function of the

depth of the tumour in relation to the surface of the gland.

Incision For deep tumours, dissection can be performed underneath

the SMAS, which can be used at the end of operation to

restore tension and avoid retromandibular depression after

The parotidectomy incision must achieve three essential

resection of the gland. For very superficial tumours, dissec-

requirements: adequate exposure of all of the parotid

tion must be strictly subcutaneous to avoid the risk of leaving

region, with the possibility of extending the incision to allow

any residual tumour cells.

neck dissection, and leaving a minimum of cosmetic seque-

lae.

The incision is drawn with a skin pencil and takes into

Dissection of the posterior part of the parotid gland

account the natural skin folds of the face and neck, clas-

sically forming a bayonet-shaped incision comprising three

All of the posterior part of the gland is released, from the

segments (Fig. 1A):

cartilaginous auditory canal superiorly to the mastoid pro-

• cess and lateral border of the SCM muscle covered by the

a vertical preauricular segment in the pretragal sulcus

superficial cervical aponeurosis inferiorly. This dissection

from the crus of the helix to the lobule;

• can be performed superoinferiorly downwards or infero-

an intermediate, horizontal or slightly upward curved seg-

superiorly using small non-toothed haemostatic forceps.

ment, flush with the insertion of the lobule and ending at

Haemostasis of veins and arteries derived from the super-

the anterior border of the mastoid;

• ficial temporal artery and vein is performed progressively

a vertical segment that descends along the anterior mar-

with bipolar cautery forceps.

gin of the sternocleidomastoid muscle (SCM), joins the

Superiorly, the fascia temporalis superficialis is rapidly

superior cervical flexion fold and descends two fingers

exposed below the zygomatic arch and above the tragal

below the anterior border of the mandible to end about

cartilage. Over the zygomatic arch, this fascia contains the

2 to 3 cm anterior to the angle of the mandible.

temporal artery and vein, which may or may not be ligated

[3,4]. More inferiorly, dissection is continued as far as the

The junction between these various segments must

anterior surface of the cartilaginous part of the external

be curved, avoiding any acute angles, especially in the

auditory canal. The cartilage is easily detached from the

region below the lobule, which predispose to skin necrosis.

gland and dissection is continued as far as the tympanic part

Numerous modifications, to varying degrees, of this basic

of the temporal bone. Dissection is performed flush with the

incision have been described, generally corresponding to

external auditory canal to avoid entering the parotid gland

cosmetic rather than oncological concerns. A first variant

parenchyma, but must remain extraperichondral. This dis-

is designed to conceal the first segment of the incision in

section is rapid, minimally haemorrhagic with no risks for

the external acoustic canal, by using the intertragic notch

the facial nerve, provided it remains on the anterior sur-

on the posterior surface of the tragus, and then in the inter-

face of the tympanic part of the temporal bone and does

tragolobular groove. A second variant is designed to conceal

not extend below the inferior margin.

the third segment of the incision in the scalp, by using a

Inferiorly and posteriorly to the lobule, the skin is dis-

facelift incision. These variants must never compromise the

sected to release and carefully avoid the posterior extension

quality of exposure of the parotid gland and the extent of

of the gland, in order to clearly visualize the mastoid inser-

tumour resection [2].

tions of the SCM.

Before dissecting the skin over the gland, the assistant

In the inferior part of the incision, the branches of the

retracts the anterior lip of the incision with a Gillis hook. A

superficial cervical plexus are released from the external

second hook is used to retract the lobule posteriorly. Once

o jugular vein, which can be spared; the most anterior nerve

the lobule has been sufficiently released with scissors, a n

branches are sectioned, while preserving auricular branches

1 silk traction suture is placed on the lobe resection margin;

supplying the external ear in the zone of the external

sutures are left long, either to receive a 200 g weight, as

auditory canal. Sparing of these branches allows optimal

recommended by Guerrier [2], or to place a large Kocher for-

preservation of lobule sensation [5]. Depending on its size,

ceps in order to retract the lobule inferiorly, perpendicularly

the posterior auricular vein can be cauterized with bipolar

to the axis of the operating table (Fig. 1B). According to

forceps or ligated.

Guerrier, use of a weight has two advantages:

The part situated between the cartilaginous part of the

external auditory canal and the mastoid process is not

•

it allows downward traction on the lobule;

released immediately, as it is situated over the course of

•

and allows haemostasis of the lobular resection margin.

the facial nerve trunk.

The anterior edge of the SCM is then released. The

Anteriorly, the superficial planes of the parotid region can

superficial cervical aponeurosis is incised using either a

be dissected in two planes:

cold scalpel or scissors. The superior part of the superficial

cervical aponeurosis is incised deeply 1 to 2 cm posteriorly

•

a strict subcutaneous plane in the subcutaneous fat;

to the anterior border of SCM until its muscle fibres and

•

underneath the Superficial Musculo-Aponeurotic System

its tendinous attachments to the mastoid are exposed, allo-

(SMAS), which, in the parotid region, is composed of the

wing safe removal of the small posterior sublobular exten-

fibrous remnant of the platysma (or cervical platysma)

sion of the gland that is intimately adherent to the most

and its aponeurosis.

superior part of the SCM. The dissection is then continued

216 C.-A. Righini

Figure 1 Diagram of the skin incision and insertion of the traction suture on the lobular resection margin. A. Elongated S-shaped

incision. 1) projection of the tip of mastoid; 2) projection of the angle of the mandible; 3) projection of the greater cornu of the

hyoid bone. B. Application of traction forceps or a weight to the lobular resection margin.

more deeply to expose the posterior belly of digastric after auricular artery, can interfere with the surgeon’s vision dur-

resecting the subdigastric lymphoid tissue (which can be ing this dissection. This artery has a variable position, but

sent for frozen section histological examination), thereby generally spirals around the nerve in an inferosuperior direc-

releasing all of the inferior part of the gland. The entire tion. It can be coagulated with bipolar forceps or, when it is

length of the inferior border of the digastric muscle is particularly large, can be clamped with haemostatic forceps

exposed as far as the intermediate tendon, and its lateral and ligated. If this artery is injured during dissection, the

surface is then released without extending beyond the supe- surgeon must not perform blind coagulation, but must apply

rior border. This part of the muscle is released at the time pressure for as long as necessary with a compress soaked in

of identification of the facial nerve. normal saline or Ringer’s lactate, together with gentle suc-

At this stage, the parotid gland is attached to posterior tion before coagulating the cut ends of the vessel, possibly

structures only by a very dense connective tissue compri- combined with irrigation depending on the proximity with

sing a rich venous plexus and containing the stylomastoid the facial nerve.

artery (branch of the posterior auricular artery), which has a The facial nerve leaves the skull at a depth of about

transverse posteroanterior course from the tympanomastoid 25 mm; three landmarks are essential to identify the nerve.

fissure to the posterior margin of the parotid gland, forming

a real tympanoparotid fascia, called Loré’s fascia [6].

Tympanomastoid suture

The tympanomastoid suture represents the junction

between the petrous and tympanic parts of the temporal

Identification of the facial nerve

bone, i.e. the junction between the tympanic part of the

temporal bone and the mastoid. It is easily identified after

The first step consists of sectioning Loré’s fascia. A Farabeuf exposing the anteroinferior quadrant on the lateral surface

retractor is placed in the dissection spaces situated superior

to and inferior to this fascia. Anterior traction on the gland

is countered by the downward traction of the lobule, which

perfectly isolates the fascia (Fig. 2). The position of retrac-

tors and the force of traction on the gland must avoid any

risk of rupture of the tumour capsule.

In the operative setting, Loré’s fascia is situated in the

same axis as the facial nerve, represented by a straight

line between attachment of the lobule to the ear and the

lower part of the ala nasae, with the nostril situated at the

zenith.

After bipolar cautery of the fascia, the fascia is sectioned

with scissor tips to expose the three essential anatomi-

cal landmarks for identification of the facial nerve trunk:

the tympanomastoid suture posteriorly, the cartilaginous

part of the external auditory canal superiorly, the poste-

rior belly of digastric inferiorly (Fig. 3A). These landmarks

are essential and sufficient to identify the facial nerve trunk Figure 2 Identification of Loré’s fascia. 1) Superior dissection

without the need for complex geometrical calculation meth- space with the first Farabeuf retractor; 2) Inferior dissection

ods [7]. The stylomastoid artery, a branch of the posterior space with the second Farabeuf retractor; 3) Loré’s fascia.

Facial nerve identification during parotidectomy 217

Figure 3 The main landmarks useful for identification of the facial nerve. A. Diagram of the main landmarks of the facial nerve

.

trunk 1) Cartilaginous part of the external acoustic canal; 2) Schwalbe’s line; 3) tympanic part of the temporal bone, which

constitutes part of the tympanomastoid suture; 4) facial nerve trunk; 5) mastoid process masked by the insertions of the SCM and

which, with the tympanic part of the temporal bone, constitutes part of the tympanomastoid suture; 6) posterior belly of digastric.

Inferior view of the skull base. 1) SMF; 2) digastric groove; 3) tympanomastoid suture; 4) styloid process. B. Lateral view of the

tympanomastoid junction. 1) tympanic bone; 2) styloid process; 3) facial nerve; 4) posterior belly of digastric; 5) tip of mastoid.

of the mastoid. It continues along the posteroinferior bor- Posterior belly of the digastric muscle

der of the tympanic part. It has a forward-opening pitchfork This muscle must be dissected as far as its insertion on

shape, at the base of which is situated the SMF from which the skull base, in the digastric groove which constitutes an

emerges the facial nerve trunk. extension of the SMF (Fig. 3B). By following the anterior bor-

der of the muscle, inferosuperiorly, the facial nerve emerges

1 cm above the superior border of the posterior belly of the

Cartilaginous part of external acoustic canal

digastric muscle at the intersection with the angle formed

More precisely, the tragal cartilage (lamina tragi) is used

by the muscle and the inferior margin of the tympanic part

as a landmark for the facial nerve. At the bone-cartilage

of the temporal bone.

junction, the tragal cartilage forms a triangular excrescence

called the triangular process, described in the literature

as Schwalbe’s line after the anatomist who described this Identification of the facial nerve trunk and its

structure for the first time. It was subsequently erroneously branches

attributed to the concha by Conley [8], who called it the

‘‘tragal pointer’’ to highlight the fact that this landmark

After identifying the site of emergence of the facial nerve,

pointed to the emergence of the facial nerve, situated

the facial nerve trunk must be dissected over its first few

7.5 mm (± 2.5 mm) anteriorly and more deeply to this point

centimetres by introducing the tips of closed scissors flat

[2].

against the nerve and by slightly separating the tips in

The tympanic part of the temporal bone can also be

a complex movement of elevation of the glandular tissue

used as a guide, as the stylomastoid foramen is situated

(discission). Dissection is performed posteroanteriorly, in

deep to its posteroinferior border (Fig. 3B). The surgeon

anterograde fashion. The nerve is perfectly identified when

slides a stripper or blunt spatula along the lateral surface

two or three of its main branches are identified. These

of the tympanic bone beyond its posteroinferior border

branches, from above downwards, are the temporal branch,

until contact with the base of the styloid process and

the buccal branch and the cervical branch (Figs. 4 A, B and

then slides it behind the styloid process and over the lat-

C). The facial nerve can now be dissected, corresponding to

eral surface of the facial nerve (Fig. 3C). The stripper

the extrafacial phase of parotidectomy.

or spatula must be advanced posteroanteriorly so that it

However, there are difficult cases in which the facial

presses posteriorly on the tympanic bone while its concavity

nerve can only be identified via a retrograde approach,

pushes the glandular tissue anteriorly. The stripper cannot

especially when the tumour presses against the extracra-

damage the facial nerve provided it is handled in this way

nial emergence of the nerve. In this setting, dissection

[9].

can be performed starting at any branch of the nerve

218 C.-A. Righini

Figure 4 Identification of the facial nerve trunk from its emergence from the stylomastoid foramen (SMF) to its main branches.

A. Identification of the nerve as it emerges from the SMF. 1) Facial nerve; 2) Schwalbe’s line; 3) posterior belly of digastric. B. Facial

nerve trunk before giving rise to its main branches. Identification of the main branches of the facial nerve. 1) temporal branch; 2)

buccal branch; 3) cervical branch.

situated anteriorly to the parotid gland. This dissection is after compression to identify the bleeding vessels, allowing

preferably performed by sacrificing the marginal mandibu- them to be coagulated safely by using irrigation. Facial nerve

lar branch, using the landmark provided by emergence of monitoring is not systematically required in patients with

the intraparotid communicating vein from the fibrous band no history of parotid surgery. Neurostimulation can be use-

between the sternocleidomastoid muscle and the angle of ful in very difficult cases when a very large tumour presses

the mandible. The vein is isolated and released from the against the facial nerve trunk, either deeply or superficially,

parotid gland. The marginal mandibular branch is situated at its emergence from the SMF, making identification of its

several millimetres medial to and parallel to this vein and is branches very difficult due to the altered anatomy of these

then followed to identify the cervical branch and finally the branches.

facial nerve trunk.

Disclosure of interest

Conclusion and keypoints

The author declares that he has no conflicts of interest con-

Any surgical procedure on the parotid gland requires pre-

cerning this article.

cise identification of the facial nerve. When no previous

surgery has been performed on the parotid gland and parotid

region, the facial nerve is identified at its third segment, References

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