TEXTBOOK AND COLOR ATLAS OF SALIVARY GLAND PATHOLOGY DIAGNOSIS AND MANAGEMENT COPYRIGHTED MATERIAL Chapter 1 Surgical Anatomy, Embryology, and Physiology of the Salivary Glands John D. Langdon, FKC, MB BS, BDS, MDS, FDSRCS, FRCS, FMedSCi Outline gual glands. In addition there are numerous minor glands distributed throughout the oral cavity within Introduction the mucosa and submucosa. The Parotid Gland On average about 0.5 liters of saliva are pro- Embryology duced each day but the rate varies throughout the Anatomy day. At rest, about 0.3 ml/min are produced, but Contents of the Parotid Gland this rises to 2.0 ml/min with stimulation. The con- The Facial Nerve tribution from each gland also varies. At rest, the Auriculotemporal Nerve parotid produces 20%, the submandibular gland Retromandibular Vein 65%, and the sublingual and minor glands 15%. External Carotid Artery On stimulation, the parotid secretion rises to 50%. Parotid Lymph Nodes The nature of the secretion also varies from gland Parotid Duct to gland. Parotid secretions are almost exclusively Nerve Supply to the Parotid serous, the submandibular secretions are mixed, The Submandibular Gland and the sublingual and minor gland secretions are Embryology predominantly mucinous. Anatomy Saliva is essential for mucosal lubrication, The Superfi cial Lobe speech, and swallowing. It also performs an essen- The Deep Lobe tial buffering role that infl uences demineralization The Submandibular Duct of teeth as part of the carious process. When Blood Supply and Lymphatic Drainage there is a marked defi ciency in saliva production, Nerve Supply to the Submandibular Gland xero-stomia, rampant caries, and destructive peri- Parasympathetic Innervation odontal disease ensue. Various digestive enzymes— Sympathetic Innervation salivary amylase—and antimicrobial agents—IgA, Sensory Innervation lysozyme, and lactoferrin—are also secreted with The Sublingual Gland the saliva. Embryology Anatomy Sublingual Ducts The Parotid Gland Blood Supply, Innervation, and Lymphatic Drainage Minor Salivary Glands EMBRYOLOGY Histology of the Salivary Glands Control of Salivation The parotid gland develops as a thickening of the Summary epithelium in the cheek of the oral cavity in the References 15 mm Crown Rump length embryo. This thicken- ing extends backward toward the ear in a plane superfi cial to the developing facial nerve. The deep Introduction aspect of the developing parotid gland produces bud-like projections between the branches of the There are three pairs of major salivary glands con- facial nerve in the third month of intra-uterine life. sisting of the parotid, submandibular, and sublin- These projections then merge to form the deep 3 4 Surgical Anatomy, Embryology, and Physiology of the Salivary Glands lobe of the parotid gland. By the sixth month inferiorly. However, on occasion it is more or of intra-uterine life the gland is completely canal- less of even width and occasionally it is triangular ized. Although not embryologically a bilobed with the apex superiorly. On average, the gland structure, the parotid comes to form a larger (80%) is 6 cm in length with a maximum of 3.3 cm in superfi cial lobe and a smaller (20%) deep lobe width. In 20% of subjects a smaller accessory joined by an isthmus between the two major divi- lobe arises from the upper border of the parotid sions of the facial nerve. The branches of the nerve duct approximately 6 mm in front of the main lie between these lobes invested in loose connec- gland. This accessory lobe overlies the zygomatic tive tissue. This observation is vital in the under- arch. standing of the anatomy of the facial nerve and The gland is surrounded by a fi brous capsule surgery in this region (Berkovitz, Langdon, and previously thought to be formed from the investing Moxham 2003). layer of deep cervical fascia. This fascia passes up from the neck and was thought to split to enclose the gland. The deep layer is attached to the man- ANATOMY dible and the temporal bone at the tympanic plate and styloid and mastoid processes (Berkovitz and The parotid is the largest of the major salivary Moxham 1988; Ellis 1997; McMinn, Hutchings, glands. It is a compound, tubuloacinar, merocrine, and Logan 1984; Williams 1995). Recent investiga- exocrine gland. In the adult, the gland is composed tions suggest that the superfi cial layer of the parotid entirely of serous acini. capsule is not formed in this way but is part of the The gland is situated in the space between superfi cial musculo-aponeurotic system (SMAS) the posterior border of the mandibular ramus and (Flatau and Mills 1995; Gosain, Yousif, and the mastoid process of the temporal bone. The Madiedo et al. 1993; Jost and Levet 1983; Mitz and external acoustic meatus and the glenoid fossa lie Peyronie 1976; Thaller, Kim, and Patterson et al. above together with the zygomatic process of the 1989; Wassef 1987; Zigiotti, Liverani, and Ghibel- temporal bone (Figure 1.1). On its deep (medial) lini 1991). Anteriorly the superfi cial layer of the aspect lies the styloid process of the temporal parotid capsule is thick and fi brous but more pos- bone. Inferiorly, the parotid frequently overlaps teriorly it becomes a thin translucent membrane. the angle of the mandible and its deep surface Within this fascia are scant muscle fi bers running overlies the transverse process of the atlas parallel with those of the platysma. This superfi cial vertebra. layer of the parotid capsule appears to be continu- The shape of the parotid gland is variable. ous with the fascia overlying the platysma muscle. Often it is triangular with the apex directed Anteriorly it forms a separate layer overlying the Figure 1.1. A lateral view of the skull showing some of the bony features 1 2 related to the bed of the parotid gland. 9 4 1: Mandibular fossa; 2: Articular emi- nence; 3: Tympanic plate; 4: Mandibu- 3 8 lar condyle; 5: Styloid process; 6: 6 5 Ramus of mandible; 7: Angle of man- dible; 8: Mastoid process; 9: External acoustic meatus. Published with per- 7 mission, Martin Dunitz, London, Langdon JD, Berkowitz BKB, Moxham BJ, editors, Surgical Anatomy of the Infratemporal Fossa. Surgical Anatomy, Embryology, and Physiology of the Salivary Glands 5 masseteric fascia, which is itself an extension of an advancement fl ap (Meningaud, Bertolus, and the deep cervical fascia. The peripheral branches Bertrand 2006). of the facial nerve and the parotid duct lie within The superior border of the parotid gland a loose cellular layer between these two sheets of (usually the base of the triangle) is closely molded fascia. This observation is important in parotid around the external acoustic meatus and the tem- surgery. When operating on the parotid gland, the poromandibular joint. An avascular plane exists skin fl ap can either be raised in the subcutaneous between the gland capsule and the cartilaginous fat layer or deep to the SMAS layer. The SMAS and bony acoustic meatus (Figure 1.2). The infe- layer itself can be mobilized as a separate fl ap and rior border (usually the apex) is at the angle of the can be used to mask the cosmetic defect following mandible and often extends beyond this to overlap parotidectomy by reattaching it fi rmly to the ante- the digastric triangle, where it may lie very close rior border of the sternocleidomastoid muscle as to the posterior pole of the submandibular salivary 1 2 2 3 4 Figure 1.2. The parotid gland and associated structures. 1: Auriculotem- poral nerve; 2: Superfi cial temporal 8 vessels; 3: Temporal branch of facial nerve; 4: Zygomatic branch of facial 9 nerve; 5: Buccal branch of facial nerve; 5 6: Mandibular branch of facial nerve; 10 7: Cervical branch of facial nerve; 8: 6 Parotid duct; 9: Parotid gland; 10: Masseter muscle; 11: Facial vessels; 11 12: Platysma muscle; 13: External 11 jugular vein; 14: Sternocleidomastoid 15 14 muscle; 15: Great auricular nerve. 7 12 Published with permission, Martin 13 Dunitz, London, Langdon JD, Berkow- itz BKB, Moxham BJ, editors, Surgical Anatomy of the Infratemporal Fossa. 6 Surgical Anatomy, Embryology, and Physiology of the Salivary Glands gland. The anterior border just overlaps the poste- rior border of the masseter muscle and the poste- rior border overlaps the anterior border of the sternocleidomastoid muscle. The superfi cial surface of the gland is covered 6 7 8 9 by skin and platysma muscle. Some terminal branches of the great auricular nerve also lie super- fi cial to the gland. At the superior border of the parotid lie the superfi cial temporal vessels with the 5 artery in front of the vein. The auriculotemporal branch of the mandibular nerve runs at a deeper 4 level just behind the superfi cial temporal vessels. The branches of the facial nerve emerge from 1 the anterior border of the gland. The parotid duct also emerges to run horizontally across the mas- 2 seter muscle before piercing the buccinator muscle anteriorly to end at the parotid papilla. The trans- 3 verse facial artery (a branch of the superfi cial tem- poral artery) runs across the area parallel to and 13 approximately 1 cm above the parotid duct. The anterior and posterior branches of the facial vein 12 emerge from the inferior border. The deep (medial) surface of the parotid 10 gland lies on those structures forming the 11 parotid bed. Anteriorly the gland lies over the mas- Figure 1.3. The mandibulostylohyoid ligament. 1: Styloid seter muscle and the posterior border of the process; 2: Stylomandibular ligament; 3: Mandibulostylo- mandibular ramus from the angle up to the condyle. hyoid ligament; 4: Masseter muscle; 5: Posterior border of As the gland wraps itself around the ramus it is ramus; 6: Lateral pterygoid muscle; 7: Medial pterygoid related to the medial pterygoid muscle at its muscle; 8: Superior pharyngeal constrictor muscle; 9: insertion on to the deep aspect of the angle.