الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The parotid gland embryologically consists of a single lobe, anatomically the facial nerve lies in a distinct plane between the anatomical superficial and deep lobes. There are fixed anatomical landmarks indicating the origin of the extracranial facial nerve as it leaves the stylomastoid foramen. The lower pole of the parotid gland is separated from the posterior pole of the submandibular gland by only thin fascia. This can lead to diagnostic confusion in determining the origin of a swelling in this area.
Among the choices for imaging of the salivary glands, CT with IV contrast is the most commonly performed procedure. Coronal and sagittal reformatted images provide excellent evaluation of soft tissues in orthogonal planes. The latest generation MDCT scanners provide rapid image acquisition reducing motion artifact and produce exquisite multiplanar reformatted images.
US has the inherent limitation of being operator dependent and poor at assessing deep lobe of the parotid gland and surveying the neck for lymphadenopathy, as well as time consuming relative to the latest generation MDCT scanners.
MRI should not be used as a primary imaging modality but reserved for special situations, such as assessment of the skull base for perineural spread of tumors. Although MRI provides similar information to CT, it is more susceptible to motion and has longer image acquisition time but has better soft tissue delineation.
PET/CT can also be utilized for initial diagnosis and staging but excels in localizing recurrent disease in post-surgical or radiation fields. Its limitation is specificity, as inflammatory diseases and some benign lesions can mimic malignant neoplasms, and malignant lesions such as adenoid cystic carcinoma may not demonstrate significantly increased uptake of FDG. A major benefit is its ability to perform combined anatomic and functional evaluation of the head and neck as well as upper and lower torso in the same setting. The serial acquisitions are fused in order to provide a direct anatomic correlate to a focus of radiotracer uptake.
Newer MRI techniques such as dynamic contrast enhancement, MR sialography, diffusion weighted imaging, MR spectroscopy, and MR microscopy are challenging PET/CT in functional evaluation of salivary gland disease and delineation of benign versus malignant tumors. However, PET/CT with novel tracers may repel this challenge. Conventional radionuclide scintigraphic imaging has largely been displaced. However, conventional scintigraphy with 99mTc-pertechnetate can be useful for the evaluation of masses suspected to be Warthin’s tumor or oncocytoma, which accumulate the tracer and retain it after washout of the normal gland with acid stimulants. The advent of SPECT/CT in a similar manner to PET/CT may breathe new life into older scintigraphic exams.
Radiology continues to provide a very significant contribution to clinicians and surgeons in the diagnosis, staging, and post-therapy follow-up of disease. Because of the complex anatomy of the head and neck, imaging is even more important in evaluation of diseases affecting this region. The anatomic and functional imaging, as well as the direct fusion of data from these methods, has had a beneficial effect on disease treatment and outcome. A close working relationship is important between radiologists and clinicians and surgeons in order to achieve these goals.
The classification of parotid tumors takes into account their cellular derivationfrom epithelial, mesenchymal, or lymphoid origins. The rarity of some of these tumors, some of which display a wide spectrum of morphological patterns within the same tumor, as well as the existence of hybrid tumors, results in a difficult task of differentiating benign from malignant tumors. For the most part, parotid tumors exist as benign or malignant neoplasms, with anticipated biologic behavior. The pleomorphic adenoma distinguishes itself as a benign tumor that may take on malignant characteristics and behavior. Some low-grade salivary gland malignancies represent highly curable neoplasms.
Gene expression profiles may be used to predict biologic behavior of salivary gland malignancies. This notwithstanding, histologic grading and clinical staging remain the two most important considerations in determining the treatment of these neoplasms and their prognosis.
Parotid gland tumors staging occurs according to size, extraparenchymal extension, lymph node involvement, the presence of metastases, and whether the facial nerve is involved, as may occur in parotid tumors. 80% of parotid tumors are benign and most commonly pleomorphic adenomas. Less than one-third of malignant tumors will have obvious clinical signs of malignancy, for example, facial nerve palsy, ulceration, fixation, or lymphadenopathy.
Routine use of CT or MR imaging does not appear justified and should be used selectively for malignant neoplasms and deep lobe tumors. Preoperative open biopsy is contraindicated and FNAB is the modality of choice for preoperative cytologic diagnosis.
Although superficial parotidectomy remains the basic surgical procedure, there is currently much debate regarding the roles of partial parotidectomy and extracapsular dissection in the management of PA. The role of the capsule and the acceptable margin for PA remain undefined. Recurrent PAs will frequently require en bloc resection due to their infi ltrative and multinodular nature. Cure in this situation is probably achieved in approximately two-thirds of cases. Management of malignant parotid tumors will depend on both the histologic diagnosis and the staging of the tumor.
Radiation therapy may be more helpful in earlier stage disease and lower-grade tumors than previously advocated. Selective neck dissection for the N0 neck may be justified in early stage disease given the high reported rate of occult nodes. The facial nerve should be preserved in parotid cancer unless it is directly infiltrated by the tumor.
The commonest parotid tumors in children are hemangiomas and hemangioendotheliomas. Medical therapy with steriods or alpha/beta interferon is preferred in the treatment of vascular parotid lesions in children. A combination of debulking and sclerosing injections to macrocystic areas is used for management of parotid lymphangiomas. Parotid lymphomas are usually associated with Sjogren’s syndrome, hepatitis C, or AIDS. Most parotid lymphomas are MALT lymphomas, which follow a fairly indolent course. The parotid lymph node bed may be the first-echelon nodes for cutaneous cancers of the cheek, ear, scalp, forehead, and temple. Metastatic parotid nodes (P) and neck nodes (N) should be staged separately when involved by primary cutaneous cancers.
Radiation therapy is given for close margins, perineural spread, and more than one positive node.
Outcome and prognosis of parotid tumors depends on: Staging, histology, lymph node metastasis, presence of pain, facial nerve paralysis and distant metastasis. Patients with both neck nodes and parotid nodes have the worst prognosis.