Chapter 58: Tumors of the Salivary Glands

INTRODUCTION

Salivary gland (SG) tumors are rare neoplasms of the neck and head which can occur in the paired major salivary glands or in one of the hundreds of minor salivary glands distributed throughout the oral cavity and pharynx. Benign neoplasms are slow growing, amenable to surgical cure, and if appropriately excised recur with a low frequency. Malignant tumors can arise from any one of the cellular components of the SG. They are generally faster growing compared to their benign counterparts and often invade into adjacent structures. A subset of malignant tumors display substantial predilection for nerve invasion which can lead to increased patient morbidity and a lower rate of surgical cure. For high-grade histologies clinical outcomes remain poor and multimodality treatment strategies are employed at most centers.^1-5 Due to the rarity of each specific malignant histology, there is a dearth of prospective clinical trial data, which limits our understanding of disease progression and the effects of specific surgical and nonsurgical interventions. A more detailed molecular characterization of SG cancers may shed additional light on the pathogenesis of this disease process and provide novel therapeutic interventions in the future.

SALIVARY GLAND ANATOMY, HISTOLOGY, AND FUNCTION

Salivary glands are exocrine glands arranged around acini composed of secretory cells.⁶ Serous, mucoserous, and mucous acini are organized around ductal structures which coalesce into larger secretory ducts (Fig. 58-1). The major SGs include two parotid glands, two submandibular glands (SMGs), and the sublingual glands. The parotid glands are primarily serous in nature and their secretions empty into the oral cavity via Stensen’s duct. One unique feature of the parotid gland is its intricate relationship with the facial nerve, which enters the gland on its posterior aspect and divides the gland into a superficial and a deep lobe. Although these terms are commonly utilized in the surgical literature, there are no fascial planes dividing the two lobes of the parotid gland (Fig. 58-2). The SMGs are found in close proximity to the lingual and hypoglossal nerves and secrete a combination of serous fluid and mucus which reaches the oral cavity through Wharton’s duct. Under baseline conditions, most salivary volume is produced by the SMGs, although under conditions of stimulation, the parotid glands can account for most surplus salivary capacity. The sublingual glands reside in close proximity to the opening of Wharton’s duct and empty primarily mucous secretions into the oral cavity through multiple excretory ducts. In addition to the major salivary glands, there are hundreds of minor SGs distributed throughout the oral cavity, including lip, soft and hard palate, floor of mouth, and buccal mucosa.⁶