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Abstract The salivary glands begin to form at 6-8 weeks’ gestation. The major salivary glands are the parotid, submandibular, and sublingual glands. Minor salivary glands are found throughout the submucosa of the upper aerodigestive tract with the highest density found within the palate. Tumors of salivary gland tissue constitute about 5% of head and neck tumors and affect major salivary glands five times more often than minor salivary glands. Most (80%) salivary gland neoplasms originate in the parotid gland, (10-15%) originate in the submandibular gland and the remainder occur in the sublingual and minor salivary glands. Tumors arising from minor salivary gland tissue carry an even higher risk for malignancy (75%). Pleomorphic adenomas (benign mixed tumors) are the most common benign SGNs, comprising 85% of all salivary gland neoplasms, 60% of all parotid neoplasms. Histologic grading of salivary gland carcinomas is important to determine the proper treatment approach. Clinical stage, particularly tumor size, may be the critical factor to determine the outcome of salivary gland cancer and may be more important than histologic grade. As for malignant tumors, they usually have more rapid rate of growth, peak age above 50 years and usually associated with pain. Physical examination shows stony hard mass fixed to the skin, deep structures and bone with facial nerve paralysis. Grossly the mass appears non-capsulated with invasion of the bone and the surrounding Summary (136) structures. Malignant tumors frequently send metastasis to the regional lymph nodes, the lungs and to the bones. Salivary gland tumors are usually slow growing and well circumscribed. Patients with a mass and findings of rapid growth, pain, paresthesias, and facial nerve weakness are at increased risk of harboring a malignancy, as peak age above 50 years. The facial nerve, which separates the superficial and deep lobes of the parotid, may be directly involved by tumors in 10 to 15% of patients. Additional findings ominous for malignancy include skin invasion and fixation to the mastoid tip. Trismus suggests invasion of the masseter or pterygoid muscles. Submandibular and sublingual gland tumors present as a neck mass or floor of mouth swelling, respectively. Malignant tumors of the sublingual or submandibular gland may invade the lingual or hypoglossal nerves, causing paresthesias or paralysis. Bimanual examination is important for determining the size of the tumor and possible fixation to the mandible or involvement of the tongue. Minor salivary gland tumors present as painless submucosal masses and are most frequently seen at the junction of the hard and soft palate. Minor salivary gland tumors arising in the prestyloid parapharyngeal space may produce medial displacement of the lateral oropharyngeal wall and tonsil. The incidence of metastatic spread to cervical lymphatics is variable and depends on the histology, primary site, and stage of the tumor. Parotid gland malignancies can metastasize to the intra- and periglandular nodes. The next echelon of lymphatics for the parotid is the upper jugular nodal chain. Although the risk of lymphatic Summary (137) metastasis is low for most salivary gland malignancies, lesions that are considered high grade or that demonstrate perineural invasion have a higher propensity for regional spread. Tumors arising in patients of advanced age also tend to have more aggressive behavior. Initial nodal drainage for the submandibular gland is the level Ia and Ib lymph nodes and submental nodes followed by the upper and midjugular nodes. Extraglandular extension of tumor and lymph node metastases are adverse prognostic factors for submandibular gland tumors. Benign and malignant tumors of the salivary glands are divided into epithelial, nonepithelial, and metastatic neoplasms. Benign epithelial tumors include pleomorphic adenoma (80%), monomorphic adenoma, Warthin’s tumor, oncocytoma, or sebaceous neoplasm. Nonepithelial benign lesions include hemangioma, neural sheath tumor, and lipoma. Malignant epithelial tumors range in aggressiveness from low to high grade. Their behavior depends on tumor histology, degree of invasiveness, and the presence of regional metastasis. The most common malignant epithelial neoplasm of the salivary glands is mucoepidermoid carcinoma. The low-grade mucoepidermoid carcinoma is composed of largely mucin-secreting cells, whereas in high-grade tumors, the epidermoid cells predominate. High-grade mucoepidermoid carcinomas resemble nonkeratinizing squamous cell carcinoma in their histologic features and clinical behavior. Adenoid cystic carcinoma, which has a propensity for neural invasion, is the second most common malignancy in adults. Skip lesions along nerves are common and can lead to treatment failures because of the difficulty in treating the full extent of invasion. Summary (138) Adenoid cystic carcinomas have a high incidence of distant metastasis, but display indolent growth. It is not uncommon for patients to experience lengthy survival despite the presence of disseminated disease. The most common malignancies in the pediatric population are mucoepidermoid carcinoma and acinic cell carcinoma. For minor salivary glands, the most common malignancies are adenoid cystic carcinoma, mucoepidermoid carcinoma, and low-grade polymorphous adenocarcinoma. Carcinoma ex pleomorphic adenoma is an aggressive malignancy that arises from a pre-existing benign mixed tumor. Diagnostic imaging is standard for the evaluation of salivary gland tumors. MRI is the most sensitive study to determine softtissue extension and involvement of adjacent structures. Dynamic contrast-enhanced MRI (DCE-MRI) can be used to possibly differentiate between benign and malignant tumors and character of the tumors. U/S can delineate location, homogeneity or heterogeneity, shape, vascularity, and margins of salivary tumors in the periauricular, buccal, and submandibular area. Diagnosis of salivary gland tumors is frequently aided by the use of FNA. In the hands of an experienced cytologist familiar with salivary gland pathology, Its sensitivity in distinguishing between benign and malignant salivary gland tumors is approximately 95%. Positron emission tomography (PET) is the only imaging technique that can image biochemical and biological processes that are fundamental to disease. FDG-PET has the highest sensitivity and specificity for detecting lymph node metastasis in head and neck cancer than MRI, U/s and CT. Summary (139) Treatment of benign neoplasms is surgical excision of the affected gland or, in the case of the parotid, excision of the superficial lobe with facial nerve dissection and preservation. The minimal surgical procedure for neoplasms of the parotid is superficial parotidectomy with preservation of the facial nerve. Enucleation of the tumor mass is not recommended because of the risk of incomplete excision and tumor spillage. Tumor spillage of a pleomorphic adenoma during removal can lead to problematic recurrences. The primary treatment of salivary malignancies is surgical excision. In this setting, basic surgical principles include the en bloc removal of the involved gland with preservation of all nerves unless directly invaded by tumor. For parotid tumors that arise in the lateral lobe, superficial parotidectomy with preservation of CN VII is indicated. If the tumor extends into the deep lobe of the parotid, a total parotidectomy with nerve preservation is performed. Although malignant tumors may abut the facial nerve, if a plane of dissection can be developed without leaving gross tumor, it is preferable to preserve the nerve. If the nerve is encased by tumor (or is noted to be nonfunctional preoperatively) and preservation would result leaving gross residual disease, nerve sacrifice should be considered. The removal of submandibular malignancies includes en bloc resection of the gland and submental and submandibular lymph nodes. Radical resection is indicated with tumors that invade the mandible, tongue, or floor of mouth. Therapeutic removal of the regional lymphatics is indicated for clinical adenopathy or when the risk of occult regional metastasis exceeds 20%. High-grade mucoepidermoid carcinomas, for example, have a high risk of regional disease and require elective treatment of the regional Summary (140) lymphatics. When gross nerve invasion is found (lingual or hypoglossal), sacrifice of the nerve is indicated with retrograde frozen section biopsies to determine the extent of involvement. If the nerve is invaded at the level of the skull base foramina, a surgical clip may be left in place to mark the area for inclusion in postoperative radiation fields. The presence of skip metastases in the nerve with adenoid cystic carcinoma makes recurrence common with this pathology. Postoperative radiation treatment plays an important role in the treatment of salivary malignancies. The presence of extraglandular disease, perineural invasion, direct invasion of regional structures, regional metastasis, and high-grade histology are all indications for radiation treatment. The optimal management of the facial nerve in parotid malignancies invading a functional nerve is unclear. In instances that the facial nerve is clearly uninvolved, the nerve should be preserved and in cases where the facial nerve is nonfunctional and invaded by tumor, most authors support resection of the nerve. When the nerve is resected, it should be reconstructed with a cable graft, using a cervical sensory nerve or the sural nerve. |