S5 Parotid Gland and Submandibular Triangle - Learning Objectives
1. What are the bony & muscular landmarks that define the parotid region?
The parotid gland is found at the inferolateral aspect of the face. The gland is located in the parotid fossa, an irregular space bordered:
- Anteriorly: ramus of mandible & masseter m.
- Posteriorly: mastoid process of temporal bone & sternocleidomastoid (SCM) m.
- Superiorly: temporomandibular joint (TMJ) & external acoustic meatus
- Inferiorly: angular tract (a thick band of connective tissue, extending from the angle of the mandible to the hyoid bone)
2.) What is the function of the parotid gland, and how does the parotid gland connect to the oral cavity?
The parotid gland is the largest of the three main salivary glands (parotid, submandibular, and sublingual - all paired). Salivary glands are exocrine glands, meaning their secretions are transported via ducts onto a surface (in this case the mucous membrane of the oral cavity). There are numerous small salivary glands that open directly or via small ducts into the oral cavity: labial, buccal, palatal, and lingual glands. Saliva is the secretion of salivary glands, and it serves multiple functions, including cleansing and moisturizing the mucous membranes of the mouth and pharynx and beginning the chemical breakdown of food.
The parotid (Stensen’s) duct typically arises at the anterior border of the parotid gland travels superficial to the masseter m., and dives deep to (and through) the buccinator m. The parotid duct is variable in path and size, but is typically 1-3 mm in diameter. The parotid duct conducts saliva from the parotid gland, through the buccinator m., opening through the papilla of parotid (Stensen’s) duct opposite the maxillary second molars.
3.) What structures are within and/or deep to the parotid gland?
Three neurovascular structures typically travel through the parotid gland (anterior to the external acoustic meatus). From superficial to deep, they are the:
- facial n. (CN VII)
- retromandibular v., and
- external carotid a.
The facial n. exits the stylomastoid foramen, then divides into two divisions: the temporofacial division (superiorly) and the cervicofacial division (inferiorly).
The superficial temporal v. typically unites with the maxillary v. to form the retromandibular v. It may divide into anterior and posterior divisions. The anterior division of the retromandibular v. typically unites with the facial v. before joining the internal jugular v. (IJV). The posterior division of the retromandibular v. typically unites with the posterior auricular v. to form the external jugular v.
The external carotid a. is a branch of the common carotid a., and is the primary source of blood to the face and superficial head. The external carotid a. has 8 branches:
- superior thyroid a.,
- ascending pharyngeal a.,
- lingual a.,
- facial a.,
- occipital a.,
- posterior auricular a.,
- maxillary a. (terminal), and
- superficial temporal a. (terminal)
These branches may be remembered by the mnemonic: Some Anatomists Like Freaking Out Poor Medical Students.
4.) What nerve provides innervation to the parotid gland (consider source, ganglion, and terminal branch)?
The parotid gland is innervated by preganglionic parasympathetic fibers originating in the glossopharyngeal n. (CN IX). These fibers synapse in the otic ganglion, which is associated in location with the deep portion of the mandibular n. (V3) trunk, just inferior to the foramen ovale. Postganglionic fibers are transmitted to the parotid gland via the auriculotemporal n. (of V3).
The auriculotemporal n. is a branch of the mandibular n. (V3). The auriculotemporal n. serves three main functions:
- transmitting secretomotor postganglionic parasympathetic fibers to the parotid gland (from the otic ganglion; preganglionic fibers from glossopharyngeal n.),
- afferently serving the temporomandibular joint (TMJ), and
- afferently serving the skin of the: tragus of ear, the external auditory meatus, and the area anterosuperior to the ear.
The cutaneous portion of the auriculotemporal n. may be found just posterior to, and accompanying, the superficial temporal a. and v. superiorly from the parotid gland.
5.) What are the boundaries and contents of the submandibular triangle?
The submandibular (digastric) triangle is the most superior region of the anterior cervical triangle. It is bordered:
- Inferiorly: anterior & posterior bellies of digastric m.
- Superiorly: mandible
This triangle typically contains the submandibular gland, facial a. & v, and hypoglossal n. (CN XII).
6.) What nerve provides innervation to the submandibular gland (consider source, ganglion, and terminal branch)?
7.) What is the function of the submandibular gland, and how does the submandibular gland connect to the oral cavity?
The submandibular gland is the primary supplier of saliva to the oral cavity. The submandibular gland is connected to the oral cavity via the submandibular (Wharton’s) duct. It traverses the space between the submandibular gland and sublingual caruncle. The duct is located between the hypoglossal n. and lingual n. in association with the hyoglossus m. The lingual n. passes deep to the duct about midway in the oral cavity. The sublingual caruncle is situated at the confluence of the sublingual folds and the lingual frenulum. The sublingual caruncle is the location where the submandibular (Wharton’s) ducts secrete saliva into the oral cavity.
8.) What are potential problems/pathologies involving the major salivary glands?
Parotid gland infection
Infections can enter the parotid region via the bloodstream, leading to parotiditis (inflammation of the parotid gland). Parotiditis can cause severe pain due to the limitations of swelling by the parotid sheath. Mumps (epidemic parotitis), a viral disease, can lead to inflammation of the parotid gland and duct.
Salivary gland stones
Salivary sialolith/calculus (sialolithiasis) are caused by the calcification/crystallization of components (in particular, calcium) of saliva. These stones can become lodged in the associated ducts (parotid, submandibular), resulting in significant pain. These are most commonly associated with the submandibular gland and duct.
Salivary gland tumor
The highest frequency of salivary gland tumors occur in the parotid gland, and most are benign. A common procedure for removal of the tumor is parotidectomy, excision of parotid gland tissue. Extreme care must be taken to not damage neurovascular structures within or deep to the parotid gland, particularly facial n. (CN VII) branches, as they are the most superficial of these structures.
The submandibular gland may also be excised in cases of tumor or calculus removal, and care to not injure the lingual n. in cases of excision of the submandibular duct.