New Trends in Management of Parotid Gland Tumors

Abstract

The salivary glands are important organs in organisms since they serve as exocrine glands in the secretion of saliva and the enzyme amylase into the oral cavity to facilitate mastication and swallowing. There are three pairs of major salivary glands. The sublingual glands that are located beneath the tongue, the submandibular glands that are located below the lower jaw, and the parotid glands that are located in front of the ears and extend to the area beneath the ear lobe along the lower border of the jaw bone. The parotid glands are the body's largest salivary glands. Tumors of the salivary glands are uncommon and represent 2-4% of head and neck neoplasms. Most (70%) salivary gland tumors (SGTs) originate in the parotid gland. The remaining tumors arise in the submandibular gland (8%) and in the minor salivary glands (22%). Although 75% of parotid gland tumors are benign, slightly more than 50% of tumors of the submandibular gland and 60-80% of minor SGTs are found to be malignant The parotid gland starts to appear and begins development at 4th to 6th week of intrauterine life. They develop from the buds that arise from the oral ectodermal lining near the angle of the stomodeum and later grow towards the ear. Ducts form by 10 weeks. Secretion commences by 18 weeks. The capsule and connective tissue develop from the surrounding mesenchyme. The parotid gland lies in the retromandibular fossa and reaches medially to the styloid process and muscles arising from it. The gland extends up to the external acoustic meatus, which is situated in a groove of the gland. It reaches posteriorly to the mastoid process and sternocleidomastoid muscle. Anteriorly, it is in contact with the posterior border of the medial pterygoid muscle and mandibular ramus. Apart of the gland extends anteriorly on the outer surface of the mandibular ramus and masseter muscle as thin triangular layer which may cover the tempro mandibular joint (TMJ) in front of the ear but never extends beyond the lower border of the zygomatic arch. Boundaries of the parotid gland are described as such: external auditory canal, ramus of mandible, and mastoid process. The gland is encased in a sheath which is continuous with the superficial musculoaponeurotic system (SMAS) and the musculature of the face. The facial nerve passes forward superfacial to the retromandibular vein and the external carotid artery and divides into its five terminal branches. Its terminal branches are Temporal, Zygomatico-orbital, Buccal, Mandibular and Cervical. In order to help find the facial nerve during a parotidectomy, several key landmarks have been described by various authors. Among the most useful are the tympanomastoid suture, the digastrics and the tragal pointer. The trunk of the facial nerve can be identified 1cm deep and inferior to the tragal pointer. Additionally the nerve is known to be lateral to the styloid process and superficial to the retromandibular vein. If the tumor makes it difficult to identify the main trunk, a retrograde dissection can help to find the nerve as well The pleomorphic adenoma or benign mixed tumor is the most common of all salivary gland neoplasms. It comprises about 70% of all parotid tumors. While mucoepidermoid carcinoma is the most common malignant neoplasm of the parotid gland and the second most common malignant tumor of the submandibular gland. It constitutes approximately 30% of all malignant tumors of the salivary glands.