الفهرس 
Anatomy of the Major Salivary GlandsOnly 14 pages are availabe for public view
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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
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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
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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.
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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.
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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
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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.