superficial to deep, the facial nerve, the auriculotemporal nerve, the retromandibular vein, and the external carotid artery pass through the substance of the parotid gland.
The facial nerve exits the skull base at the stylomastoid foramen. The surgical landmarks are important (Figure 1.4). To expose the trunk of the facial nerve at the stylomastoid foramen, the dissection passes down the avascular plane between the parotid gland and the external acoustic canal until the junction of the cartilaginous and bony canals is palpated. A small triangular extension of the cartilage points toward the facial nerve as it exits the foramen (Langdon 1998b). This is the so‐called tragal pointer. The main trunk of the nerve lies approximately 13.6 mm from this landmark but there is considerable variation (Ji et al. 2018). The nerve lies about 9 mm from the posterior belly of the digastric muscle where the digastric passes deep to the sternocleidomastoid muscle, and 11 mm from the bony external meatus (Holt 1996). The facial nerve then passes downwards and forwards over the styloid process and associated muscles for about 1.3 cm before entering the substance of the parotid gland (Hawthorn and Flatau 1990). The first part of the facial nerve gives off the posterior auricular nerve supplying the auricular muscles and also branches to the posterior belly of the digastric and stylohyoid muscles.
On entering the parotid gland, the facial nerve divides into two divisions, temporofacial and cervicofacial the former being the larger. The division of the facial nerve is sometimes called the pes anserinus due to its resemblance to the foot of a goose. From the temporofacial and cervicofacial divisions, the facial nerve gives rise to five named branches – temporal, zygomatic, buccal, mandibular, and cervical (Figure 1.5). The peripheral branches of the facial nerve form variable anastomotic arcades between adjacent branches to form the parotid plexus. These anastomoses are important during facial nerve dissection as accidental damage to a small branch often fails to result in any facial weakness due to dual innervation from adjacent branches. Davis et al. (1956) studied these patterns following the dissection of 350 facial nerves in cadavers. The anastomotic relationships between adjacent branches fell into six patterns (Figure 1.6). They showed that in only 6% of cases (type VI) is there any anastomosis between the mandibular branch and adjacent branches. This explains why, when transient facial weakness follows facial nerve dissection, it is usually the mandibular branch that is affected.
Auriculotemporal Nerve
The auriculotemporal nerve arises from the posterior division of the mandibular division of the trigeminal nerve in the infratemporal fossa. It runs backward beneath the lateral pterygoid muscle between the medial aspect of the condylar neck and the sphenomandibular ligament. It enters the anteromedial surface of the parotid gland passing upwards and outwards to emerge at the superior border of the gland between the temporomandibular joint and the external acoustic meatus. This nerve communicates widely with the temporofacial division of the facial nerve and limits the mobility of the facial nerve during surgery (Flatau and Mills 1995). Further communications with the temporal and zygomatic branches loop around the transverse facial and superficial temporal vessels (Bernstein and Nelson 1984).
Figure 1.4. Anatomical landmarks of the extratemporal facial nerve.
Figure 1.5. Clinical photograph of dissected facial nerve following superficial parotidectomy.
Source: Published with permission, Martin Dunitz, London, Langdon JD, Berkowitz BKB, Moxham BJ, editors, Surgical Anatomy of the Infratemporal Fossa. DOI: 10.1002/9781118949139.ch1.
Retromandibular Vein
The vein is formed within the parotid gland by the union of the superficial temporal vein and the maxillary vein. The retromandibular vein passes downwards and close to the lower pole of the parotid where it often divides into two branches passing out of the gland. The posterior branch passes backward to unite with the posterior auricular vein on the surface of the sternocleidomastoid muscle to form the external jugular vein. The anterior branch passes forward to join the facial vein.
The retromandibular vein is an important landmark during parotid gland surgery. The division of the facial nerve into its temporofacial and cervicofacial divisions occurs just behind the retromandibular vein (Figure 1.7). The two divisions lie just superficial to the vein in contact with it. It is all too easy to tear the vein while exposing the division of the facial nerve!
Figure 1.6. The branching patterns of the facial nerve.
Source: Berkovitz et al. 2003/Taylor & Francis.
| I Type I, 13% | V Type V, 9% | 3 Buccal branch |
| II Type II, 20% | VI Type VI, 6% | 4 Mandibular branch |
| III Type III, 28% | Temporal branch | 5 Cervical branch |
| IV Type IV, 24% | 2 Zygomatic branch |
Figure 1.7. The facial nerve and its relationship to the retromandibular vein within the parotid gland.
Source: Published with permission, Martin Dunitz, London, Langdon JD, Berkowitz BKB, Moxham BJ, editors, Surgical Anatomy of the Infratemporal Fossa. DOI: 10.1002/9781118949139.ch1.
1 Facial nerve at stylomastoid foramen
2 Temporofacial branch of facial nerve
3 Cervicofacial branch of facial nerve
4 Temporal branch of facial nerve
5 Zygomatic branch of facial nerve
6 Buccal branch of facial nerve
7 Mandibular branch of facial nerve
8 Cervical branch of facial nerve
9 Posterior belly of the digastric muscle
10 Retromandibular vein and external carotid artery
External Carotid Artery
The external carotid artery runs deeply within the parotid gland. It appears from behind the posterior belly of the digastric muscle and grooves the parotid before entering it. It gives off