Johan Fagan

The facial nerve is central to parotid surgery for both surgeon and patient. Knowledge of the surgical anatomy and the landmarks to find the facial nerve are the key to preserving facial nerve function.

Surgical Anatomy

Parotid gland

The parotid glands are situated anteriorly and inferiorly to the ear. They overlie the vertical mandibular rami and masseter muscles, behind which they extend into the retromandibular sulci. The glands extend superiorly from the zygomatic arches and inferiorly to below the angles of the mandible where they overlie the posterior bellies of the digastric and the sternocleidomastoid muscles. The parotid duct exits the gland anteriorly, crosses the masseter muscle, curves medially around its anterior margin, pierces the buccinator muscle, and enters the mouth opposite the 2nd upper molar tooth.

Superficial Muscular Aponeurotic System and Parotid Fascia

The Superficial Muscular Aponeurotic System (SMAS) is a fibrous network that invests the facial muscles, and connects them with the dermis. It is continuous with the platysma inferiorly; superiorly it attaches to the zygomatic arch. In the lower face, the facial nerve courses deep to the SMAS and the platysma. The parotid glands are contained within two layers of parotid fascia, which extend from the zygoma above and continue as cervical fascia below.

Structures that traverse, or are found within the parotid gland

Fig 1
Figure 1: Main branches of facial nerve
Fig 2
Figure 2: Branches of external carotid artery

Relevant surgical relations

Posterior: Cartilage of external auditory meatus; tympanic bone, mastoid process, sternocleidomastoid muscle

Deep: Styloid process, stylomandibular tunnel, parapharyngeal space, posterior belly of digastric, sternocleidomastoid muscle

Superior: Zygomatic arch, temporomandibular joint

Facial nerve

The facial nerve exits the stylomastoid foramen, and enters the parotid gland. Although the branching pattern does vary from patient to patient, the trunk generally divides at the pes anserinus into upper and lower divisions that subsequently branch into temporal (frontal), zygomatic, buccal, marginal mandibular and cervical branches that innervate the muscles of facial expression. Small branches to the posterior belly of digastric, stylohyoid, and auricular muscles also arise from the trunk (Figure 3).

Fig 3
Figure 3: The facial nerve trunk dividing into superior and inferior divisions at the pes anserinus

The nerve traverses the parotid gland, with about 2/3 of the gland substance being superficial to the nerve. As parotid dissection generally is directed along the facial nerve, the nerve in effect divides the parotid from a surgical perspective into superficial and deep lobes, although there is no natural soft tissue dissection plane that separates the two lobes.

The midfacial nerve branches have multiple cross-innervations; however the frontal and marginal mandibular branches do not have cross-innervations and injury to these branches is followed by paralysis of the forehead and depressors of the lower lip (Figure 4). Therefore unlike the temporal and marginal mandibular nerves, selected midfacial branches may be sacrificed without loss of facial function.

Fig 4
Figure 4: Midfacial branches (yellow) interconnect whereas temporal and marginal mandibular (black) do not

Locating the Facial Nerve

It is useful to know preoperatively whether a parotid tumour is situated deep or superficial to the facial nerve. This facilitates surgical planning and facilitates preoperative consent relating to the likelihood of a temporary postoperative facial nerve weakness.

Surface markings

Facial nerve trunk: The trunk exits the skull at the stylomastoid foramen. This is situated at the deep end of the tympanomastoid suture line, which can be located at the junction between the mastoid process and the tympanic ring of the external ear canal

Temporal (frontal) branch of facial nerve: The nerve crosses the zygomatic arch; it runs within the SMAS and lies superficial to the deep temporalis fascia. It courses more or less along a line drawn between the attachment of the lobule of the ear to a point 1.5 cm above the lateral aspect of the eyebrow. To avoid injury to the temporal branch dissect either in a subcutaneous plane or deep to the SMAS (Figure 1).


Radiological investigation is not routinely required with parotid tumours. It is recommended for surgical planning with tumours that are large, fixed, and are associated with facial nerve involvement, trismus, and parapharyngeal space involvement. MRI is a valuable investigation with recurrence of pleomorphic adenoma as it is often multifocal.

The extratemporal facial nerve is not visible with ultrasound, CT or MRI. The retromandibular vein is however intimately associated with the facial nerve. The vein courses through the parotid gland immediately deep to the facial nerve, but rarely runs immediately superficial to the nerve (Figures 5 & 6). Reliance is therefore placed on the juxtaposition of the retro-mandibular vein and the nerve to predict whether a tumour is likely to be deep or superficial to the nerve.

Fig 5
Figure 5: Facial nerve running superficial to retromandibular vein
Fig 6
Figure 6: Facial nerve running deep, but close, to retromandibular vein

The retromandibular vein can be clearly visualized on a CT with contrast, or an MRI (Figures 7, 8).

Fig 7
Figure 7: Red arrows indicate retromandibular veins, and yellow arrow the course of the facial nerve in a superficial lobe pleomorphic adenoma
Fig 8
Figure 8: Red arrows indicate retro-mandibular veins, and yellow arrow the course of the facial nerve in a deep lobe pleomorphic adenoma

Radiology may also alert the surgeon to extension of a deep lobe parotid tumour through the stylomandibular tunnel into the parapharyngeal space (Figure 9).

Fig 9
Figure 9: Tumour passing through stylomandibular tunnel to parapharyngeal space (Arrow indicates styloid process)

Intraoperative location of facial nerve

The facial nerve is usually explored by prograde dissection i.e. by locating the nerve trunk where it exits from the stylomastoid foramen, and then dissecting anteriorly along the trunk, the pes anserinus and the divisions and nerve branches. Occasionally this is not possible e.g. with a large fixed mass centered at the stylomastoid foramen. In such cases a retro-grade dissection may be required after locating the temporal branch where it crosses the zygoma, the buccal branches which lie parallel to the parotid duct (Figure 10), or the marginal mandibular branch where is crosses the facial artery and vein just below or at the inferior margin of the mandible, where it is just deep to platysma (Figure 11).

Fig 10
Figure 10: Buccal branches adjacent to the parotid duct
Fig 11
Figure 11: Marginal mandibular nerve crossing facial artery and vein

The surgical landmarks for finding the facial nerve trunk at the stylomastoid fora-men are remarkably constant, and all the landmarks should be identified at every operation to facilitate finding the nerve (Figures 12, 13).

Fig 12
Figure 12: Schematic surgical landmarks for the facial nerve trunk
Fig 13
Figure 13: Intraoperative surgical land-marks for the facial nerve trunk

Posterior belly of digastric muscle: The nerve runs at the same depth below the skin surface, and bisects the angle between the muscle and the styloid process

Cartilage pointer: This refers to the medial-most, pointed end of the cartilage of the external auditory meatus. The nerve exits the foramen approximately 1cm deep and 1cm inferior to this point

Tympanic ring, mastoid process and tympanomastoid suture line: The tympanomastoid suture line is the most precise landmark for the facial nerve as it leads medially, directly to the stylomastoid foramen

Styloid process: The facial nerve crosses the styloid process. Palpating the styloid process is therefore a useful means to determine the depth and position of the facial nerve

Branch of occipital artery: A small branch of the occipital artery is commonly encountered just lateral to the facial nerve close to the stylomastoid foramen. Brisk arterial bleeding should therefore alert the surgeon to the proximity of the facial nerve; it is easily controlled with bipolar cautery.

Electrical stimulation and monitoring

These need not be routinely employed, but may be useful adjuncts to a sound know-ledge of facial nerve anatomy in selected cases such as revision surgery and with large tumours. It may however not record facial stimulation with faulty equipment, and nerve fatigue following excessive mechanical or electrical stimulation, and use of a muscle relaxant.

Types of Parotidectomy

Preoperative consent

Scar: Usually very good healing except over the mastoid where some scarring may occur


Partial/Superficial Parotidectomy

Fig 14
Figure 14: "Lazy-S” incision; Corners of eye and mouth exposed
Fig 14
Figure 15: Exposure of parotid mass or gland
Fig 16
Figure 16: Expose the sternomastoid and posterior belly of digastric muscle
Fig 17
Figure 17: Posterior branch of greater auricular nerve (arrow)
Fig 18
Figure 18: Identify facial nerve landmarks
Fig 19
Figure 19: Location of facial nerve trunk, and superior and inferior release of capsule and parotid tissues (yellow arrows)
Fig 20
Figure 20: Strip the superficial lobe off the branches of facial nerve

Fig 20
Figure 21: Completed superficial parotidectomy; note nerve crossing retromandibular vein

Parotid dissection for deep lobe tumours

The principles of resecting deep lobe tumours are to:

Fig 22
Figure 22: Facial nerve has been freed from deep lobe
Fig 23
Figure 23: Reflecting superficial lobe for access to facial nerve and to deep lobe tumour
Fig 24
Figure 24: Tumour resected by removing tumour between splayed facial nerve branches
Fig 25
Figure 25: Access to parapharyngeal space tumour extension by reflecting the superficial lobe and division of styloid process
Fig 26
Figure 26: Completed total parotidectomy in patient shown in Figure 22; silk ties are on branches of the external carotid artery

Tumour spillage

Great care should be taken to avoid rupture and spillage of pleomorphic adenoma tis-sue into the operative site as it may lead to multifocal tumour recurrence, often more than 20yrs following surgery (Figure 27). A minor controlled capsular rupture may be simply managed by copiously irrigating the wound. With more extensive ruptures, especially of a pleomorphic adenoma in the parapharyngeal space, some would advocate postoperative radiation therapy. Due to the multifocal nature of the recurrence, MRI is an important preoperative investigation for recurrence. Having to operate in a previously dissected field, the facial nerve is at greater risk of injury, and should be monitored during surgery.

Fig 27
Figure 27: Multifocal recurrence of pleomorphic adenoma

Wound closure

Facial nerve repair

Unlike with malignant tumours, the facial nerve and its branches can virtually always be dissected free from benign neoplasms. Isolated midfacial branches may be sacrificed without causing visible facial dysfunction. Transection of the temporal (frontal) and marginal mandibular nerves however results in disfiguring facial asymmetry; these nerves should be repaired with 8/0 nylon/prolene epineural sutures. When primary nerve repair is not possible due to undue tension or nerve resection, then the nerve can be grafted with greater auricular nerve, or sural nerve.

The greater auricular nerve is approximately the same diameter as the facial nerve trunk, and has a few branches that can be used to graft more than one facial nerve branch (Figure 28).

Fig 28
Figure 28: Greater auricular nerve

The sural nerve provides greater length and more branches and is better suited to bridging longer defects and for grafting to more peripheral branches (Figures 29, 30).

Fig 29
Figure 29: Sural nerve

When the proximal end of the facial nerve is not available, e.g. with extensive proximal perineural tumour extension, then a hypoglossal-facial nerve interposition graft can be used to restore facial tone and movement. The nerve graft is sutured end-to-end to the distal facial nerve(s), and end-to-side to the hypoglossal nerve after cutting about 25% into the side of the hypoglossal nerve to expose the nerve axons (Figure 31).

Fig 30
Figure 30: Sural nerve graft
Fig 31
Figure 31: Hypoglossal/facial nerve graft

Author & Editor

Johan Fagan MBChB, FCORL, MMed
Professor and Chairman
Division of Otolaryngology
University of Cape Town
Cape Town, South Africa