الفهرس 
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Abstract
Summary
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
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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.
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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.
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The classic presentation of a benign SGT is a painless, slow-growing mass on the face (parotid), angle of the jaw (parotid tail, submandibular), or neck (submandibular) or a swelling at the floor of the mouth (sublingual). A sudden increase in size may be indicative of infection, cystic degeneration, hemorrhage inside the mass, or malignant degeneration. Benign SGTs are almost always freely mobile, and for masses that arise in the parotid gland, facial nerve function should be normal.
The most common sign and symptoms are parotid mass (96.9%), pain (40.4%), enlarged cervical lymph nodes (32.0%), facial nerve palsy (20.6%) and overlying skin infiltration (19.8%). In 20% of cases there is no symptoms of tumour malignancy. The average duration of symptoms suggesting malignancy is 4 months. The subsequent poor prognostic factors are: skin infiltration, enlarged cervical lymph nodes, tumour fixation and tumour size (>4cm).
Exposures to tobacco smoke and alcohol intake have not been found consistently associated with its development. However, one of the well-established risk factors is exposure to ionizing radiation, as supported by studies on atomic bomb survivors Medical radiation or ultraviolet light therapeutic treatments to the head or neck and exposures to full-mouth
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dental X-rays have also been linked to an increased risk. The effect of UV therapeutic light seems to be more evident in fair-skinned persons, who are naturally more sensitive to the effects of UV light. Additionally, nitroso compounds have induced parotid gland tumors in laboratory mice. The presence of nitroso compounds in rubbers could explain the higher incidence of parotid gland cancer in rubber industrial workers.
Advances in imaging have led to improved sensitivity in the diagnosis of diseases that involve the major salivary glands. Ultrasound (US), plain radiography and sialography, magnetic resonance imaging (MRI), computed tomography (CT), and nuclear scintigraphy {positron emission tomography (PET)} all play a part, and imaging often assists in the planning of further management, operative or otherwise.
The value of fine needle aspiration cytology (FNAC) and frozen section (FS) in the diagnosis of malignant parotid tumour. FNAC is an important examination that provides valuable information for the preoperative diagnostic work-up and alerts the surgeon to the possible presence of malignancy. However, FNAC cannot be used alone, and FS
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has a very important place in the intraoperative management of parotid tumours
Superficial parotidectomy is the treatment of choice for most benign tumors in the superficial lobe. In order to preserve the facial nerve, it is important to try to determine the proximity of the nerve to the capsule of the tumor prior to surgery. Results of a retrospective review showed that malignant tumors are likely to have a positive facial nerve margin.
Conventional total superficial parotidectomy (TP) has commonly been used, but partial superficial parotidectomy (PP) offers the possibility of better preserving glandular function and avoiding palsy of the facial nerves. The incidence of transient facial paralysis was significantly lower in patients who received PP than in those who received TP. Secretory function is preserved for patients with a conserved Stensen’s duct, whereas patients in whom the duct is ligated lose secretory function. Partial superficial parotidectomy reduces the incidence of postoperative facial nerve dysfunction and is conducive to preserving Stensen’s duct and saliva secretion.
New targeted therapeutics and novel agents are also being developed for the systemic treatment of parotid
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malignancies the epidermal growth factor receptor (EGFR) is one of the major targets under intensive investigations since it has been found to be overexpressed in head and neck squamous cell carcinoma. This overexpression has been linked to disease recurrence in which EGFR-dependent signaling pathways are activated, leading to tumor cell proliferation and anti-apoptosis. EGFR blockade has hence been proposed to inhibit tumor growth.