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Radiology > HEAD AND NECK
Parotid, Malignant Tumors
Article Last Updated: May 14, 2004
AUTHOR AND EDITOR INFORMATION
Section 1 of 13  
Author: Scott Vanderheiden, MD, Consulting Radiologist, Radia Medical Imaging, Providence Everett Medical Center, Colby Campus
Scott Vanderheiden is a member of the following medical societies: Alpha Omega Alpha, American College of Radiology, and Radiological Society of North America
Editors: Barton F Branstetter IV, MD, Associate Professor of Radiology, Otolaryngology, and Biomedical Informatics, University of Pittsburgh; Director of Head and Neck Imaging, Clinical Director of Neuroradiology, Department of Radiology, Division of Neuroradiology, University of Pittsburgh Medical Center; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; C Douglas Phillips, MD, Professor, Departments of Radiology, Neurosurgery, and Otolaryngology, University of Virginia Health Sciences Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Lawrence M Davis, MD, Assistant Professor of Diagnostic Imaging (Clinical), Department of Diagnostic Imaging, Warren Alpert Medical School at Brown University
Author and Editor Disclosure
Synonyms and related keywords:
parotid tumor, parotid gland tumors, parotid cancer, parotid gland cancer, salivary glands, salivary gland tumors, salivary gland cancer, salivary cancer, malignant parotid neoplasm, salivary gland neoplasm, salivary neoplasm, mucoepidermoid carcinoma, adenoid cystic carcinoma, malignant mixed tumor, acinic cell carcinoma, undifferentiated carcinoma, parotid malignancy, parotid neoplasms
Background
Parotid is a Greek word that means near the ear. Parotid glands are the largest of the salivary glands. They are paired glands that contain both mucus and serous cells and a ductal network.
Pathophysiology
Most primary tumors of the parotid glands arise from 1 of 2 histologic cell subtypes: epithelial tumors arising from ductal cells and glandular tumors from salivary unit cells. The most common metastases to the intraparotid lymph nodes are from melanoma and squamous cell carcinoma of the head and neck.
Frequency
United States
Malignant tumors of the parotid gland are rare. The incidence of salivary gland tumors is 1-2 cases per 100,000 people. Of these, 85% occur in the parotid gland, representing 0.6% of tumors in the body.
Only 20% of parotid neoplasms are malignant. The most common malignant parotid neoplasm in adults is mucoepidermoid carcinoma, which represents almost one third of all malignant tumors.
Mortality/Morbidity
Depending on the histologic type and tumor grade, the morbidity and mortality can vary greatly. Some benign tumors can be aggressive locally and recur following their removal. Morbidity is proportional to the degree of invasion at the time of detection.
- Some malignant tumors are slow growing with high 5-year survival rates in patients. Poor prognostic signs are the following: (1) high-grade tumor, (2) lymph node or distant metastasis at diagnosis, (3) facial nerve paralysis, (4) skin involvement, (5) high tumor stage, (6) deep lobe involvement, and (7) recurrent tumor.
- Pain does not indicate that a neoplasm is malignant; however, in patients with known malignancy, pain is a poor prognostic sign.
Race
Eskimos are at increased risk for undifferentiated lymphoepithelial carcinoma.
Sex
Overall, parotid tumors are slightly more common in women than in men.
Age
Most parotid tumors occur in patients aged 30-70 years. Parotid tumors are more likely to be malignant in children (approximately 35%) than in adults.
- The most common malignant parotid tumors in adults are the following: (1) mucoepidermoid carcinoma, (2) adenoid cystic carcinoma, and (3) malignant mixed tumor.
- The most common malignant parotid tumors in children are the following: (1) mucoepidermoid carcinoma, (2) acinic cell carcinoma, and (3) undifferentiated carcinoma.
Anatomy
The parotid gland is enveloped by the superficial layer of the deep cervical fascia. The gland is artificially divided into the superficial (80%) and deep (20%) lobes, which are separated by the facial nerve. The deeper portion of the gland lies between the anterior border of the sternocleidomastoid and the posterior belly of the digastric muscles. Most of the gland is located posterior and lateral to the ascending ramus and angle of the mandible. The Stensen duct drains the ductal system of the parotid and enters the oral cavity near the upper second molar tooth. Several lymph nodes normally are present within each gland.
Clinical Details
A typical parotid malignancy is a painless, unilateral enlargement of the gland. The purpose of radiologic examination is to define the size and anatomy of the mass, differentiate the intraglandular origin from extraglandular origin, determine its benign and malignant characteristics, and provide important preoperative information such as the location of the facial nerve.
The workup begins with a history and physical examination. FNA of the mass may be performed. The accuracy of FNA for diagnosis depends strongly on the quality of the specimen and the experience of the cytopathologist. Bartels et al reported no increase in accuracy by adding FNA to cross-sectional imaging study.
Preferred Examination
CT and MRI are the modalities of choice for imaging parotid neoplasms. Both have sensitivities that approach 100%. Both modalities have the ability to depict the entire gland and concomitantly show the contralateral gland.
Each modality has special benefits and limitations. MRI is the preferred modality for evaluating a painless parotid mass. CT is well suited for evaluating recurrent, tender parotid masses that can be inflammatory. Plain radiographs or CT demonstrate invasion the earliest. Nuclear medicine studies lack the resolution to show bony invasion. Most malignant tumors are cold on scintigraphy. Combining fine-needle aspiration (FNA) with MRI offers no greater accuracy compared with that of either test alone.
Limitations of Techniques
On CT or MRI, many malignant tumors, such as acinic cell carcinomas or low-grade mucoepidermoid carcinomas, appear indistinguishable from benign tumors, such as pleomorphic adenomas.
Branchial Cleft Cysts
Cystic Hygroma
Liposarcoma, Soft Tissue
Parotid, Pleomorphic Adenoma
Schwannoma, Cranial Nerve
Other Problems to be Considered
Malignant or premalignant parotid neoplasms
Carcinoma ex pleomorphic adenoma
Malignant mixed tumor
Mucoepidermoid carcinoma
Adenoid cystic carcinoma
Acinic cell carcinoma
Polymorphous low-grade adenocarcinoma
Salivary duct carcinoma
Basal cell adenocarcinoma
Adenocarcinoma, not otherwise specified
Clear cell carcinoma
Epithelial myoepithelial carcinoma
Sebaceous neoplasm of salivary gland origin
Primary squamous cell carcinoma
Metastasis
Lymphoma
Benign neoplasms
Warthin tumor or adenolymphoma
Oncocytoma
Oncocytic papillary cystadenoma
Myoepithelioma
Sialadenoma papilliferum
Inverted ductal papilloma
Lipoma
Schwannoma and neurofibroma
Hemangioma
Granulomatous diseases
Sarcoid
Tuberculosis
Cat scratch disease
Actinomycosis
Vascular and lymphatic malformations
Arteriovenous malformation
Hemangioma
Lymphangioma
Other considerations
Inflammatory disease
Parotid cysts
Sialadenosis
Hyperplasia or hypertrophy of salivary glands
Sjögren syndrome
Mikulicz disease or sicca syndrome
Findings
Plain-film evaluation of the parotid gland is of limited clinical value. Radiographs can demonstrate sialolithiasis or involvement of the adjacent mandible. Views used to examine the parotid gland include open-mouth lateral images with an extended chin, posteroanterior images, and bilateral oblique images.
Sialography, or the injection of water-soluble contrast material into the Stensen duct, is used to demonstrate ductal anatomy or sialoliths.
Degree of Confidence
CT is 10 times more sensitive than plain radiography in detecting small calcium deposits.
The sensitivity of sialography in detecting tumor is 85% at best, when performed by an experienced examiner. This rate is low compared with that of CT and MRI. Sialography is contraindicated or not recommended in the workup for a suspected malignant parotid tumor because come believe that the pressure generated by the injection of contrast material can disseminate tumor cells. Sialography should be reserved for the diagnosis of inflammatory conditions.
Findings
CT findings of diffuse glandular calcifications suggest chronic sialadenitis, whereas calcifications within a mass are commonly seen in a pleomorphic adenoma. A solid mass is more easily differentiated from a cystic mass using CT compared to MRI. Although the facial nerve usually is not visualized on CT, the course of the nerve can be traced from the stylomastoid foramen. In addition, the Stensen duct usually is not seen unless it is dilated.
Degree of Confidence
CT has advantages and limitations in imaging the parotid gland. Direct axial and coronal images can be obtained quickly in most patients; usually, only axial images are obtained. CT is superior in detecting heterotopic calcification or invasion of the mandible or skull base.
Dental-amalgam streak artifact can seriously degrade image quality; however, changing the gantry angle can reduce this degradation. In some patients with a dense parotid gland, a small tumor or diffuse cell infiltration cannot be detected. Furthermore, direct coronal images cannot be obtained in some patients who cannot extend their necks.
False Positives/Negatives
The CT appearance of benign and malignant tumors can overlap. A low-grade mucoepidermoid carcinoma can be cystic and contain calcifications, much like a pleomorphic adenoma. Higher-grade tumors tend to be more attenuating and more homogeneous.
Findings
Certain MRI characteristics can help differentiate benign parotid masses from malignant masses. A benign lesion usually is marginated smoothly, with a distinct border or capsule; however, many low-grade malignancies have a pseudocapsule and a benign radiographic appearance. High-grade malignancies have ill-defined infiltrating margins.
In cases of a pleomorphic adenoma, T1-weighted images typically demonstrate intermediate signal intensity, with isointense-to-hyperintense signal on T2-weighted images. Contrast enhancement can be homogeneous or heterogeneous.
A Warthin tumor has homogeneous intermediate-to-hyperintense signal on T1-weighted images and intermediate signal intensity with focal hyperintense areas on T2-weighted images. Typically, these tumors are not contrast enhancing.
As a result of increased cellularity and decreased mucous production, high-grade malignancies tend to have low signal intensity with both T1- and T2-weighted sequences, whereas benign and low-grade malignancies are bright on T2-weighted images.
Common benign pleomorphic adenoma can evolve into malignant carcinoma ex pleomorphic adenoma or malignant mixed tumor. MRI can demonstrate the change from high T2 signal intensity with benign tumors to low-to-intermediate T2 signal with malignant tumors.
Degree of Confidence
MRI is superior to CT in demonstrating tumor margins, and MRI is the procedure of choice for evaluating a nontender palpable parotid mass. Occasionally, the facial nerve or Stensen duct can be visualized. Common sequences are T1-weighted, T2-weighted, and inversion recovery fast spin-echo sequences.
MRI contrast agents are controversial and usually reserved for use when a palpable mass is not seen on a nonenhanced study. The use of contrast agents is indicated in evaluating the postoperative gland.
Magnetic resonance spectroscopy is currently under investigation as a tool in diagnosing parotid masses.
False Positives/Negatives
Low-grade mucoepidermoid carcinomas can appear identical to pleomorphic adenomas.
Findings
In the parotid gland, ultrasonography (US) is used to differentiate solid from cystic lesions. US often can be used to determine whether a lesion is intraglandular. The real-time capability of US makes it useful for guiding needle biopsy.
Parotid US uses a linear, high-frequency transducer (of 7-10 MHz) that provides high-resolution images. However, imaging depth is compromised. The deep lobe of the gland usually is not seen well.
Degree of Confidence
US is not routinely used as an imaging modality because of the greater sensitivity of CT and MRI.
Findings
The parotid and other salivary glands concentrate technetium-99m pertechnetate; however, nuclear medicine studies are not the preferred imaging modality for evaluating a parotid mass. Gallium-67 citrate, technetium-99 pertechnetate, and thallium-201 chloride have been used to evaluate parotid tumors.
Degree of Confidence
Nuclear medicine studies lack the resolution to show bony invasion. Most malignant tumors are cold on scintigraphy.
In detecting malignant parotid tumors, gallium-67 citrate scanning has a sensitivity of 85% and specificity of 38%. The low specificity is secondary to uptake by a pleomorphic adenoma.
Scanning with 99mTc pertechnetate has 75% sensitivity and 88% specificity for evaluating oncocytoma or Warthin tumor.
As a single test, cross-sectional imaging such as CT or MRI provides more information than scintigraphy.
False Positives/Negatives
With technetium, most tumors are relatively photopenic compared with the remainder of the gland and easily missed. Decreased activity in the gland is nonspecific and can represent benign or malignant neoplasm, metastasis, abscess, focal atrophy, or the changes of Sjögren syndrome. Two neoplasms—Warthin tumor and oncocytoma—concentrate pertechnetate and are seen easily.
Findings
Angiography has virtually no role in diagnosing parotid neoplasms and is reserved for embolizing vascular lesions.
Surgical excision is the preferred treatment, with superficial or total parotidectomy depending on the stage and histology of the tumor. Small low-grade tumors are treated with a superficial parotidectomy when possible. Neck dissection should be considered when evaluating node positive disease. A locally invasive tumor may require resection of the facial nerve, skull base, or mandible. Postoperative radiation therapy is recommended when surgical margins are positive, tumors are high grade or larger than 4 cm, or local extension is noted. Chemotherapy has not been proven effective.
Medical/Legal Pitfalls
- Benign tumors, such as the pleomorphic adenoma, can recur locally (1-50% of cases).
- The risk is highest when the tumor is enucleated without postoperative radiation therapy.
- As a result, repeat excision and/or radiation therapy may be needed.
- A malignant mixed-cell tumor can arise from a prior benign adenoma.
- Occasionally, injury to the facial nerve is an unavoidable consequence of parotidectomy.
- Frey syndrome is a postoperative complication in which patients experience facial sweating and flushing during mastication.
- The etiology is believed to involve injury to the postganglionic sympathetic nerve fibers that supply the sweat glands of the skin.
- The incidence is 10-100%.
The authors and editors gratefully acknowledge Manferd Benson, MD, for his contributions made to this topic.
| Media file 1:
Parotid, malignant tumors. Axial T1-weighted MRI demonstrates a low-signal-intensity mass in the left parotid gland. Pathology indicated mucoepidermoid carcinoma. |
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| Media file 2:
Parotid, malignant tumors. Axial T1-weighted MRI with fat saturation and contrast enhancement shows an infiltrative, enhancing mass involving the superficial and deep lobes of the left parotid gland. Pathology indicated a mucoepidermoid carcinoma. |
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Media type: MRI
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| Media file 3:
Parotid, malignant tumors. Contrast-enhanced neck CT scan demonstrates a well-circumscribed, enhancing mass in the superficial right parotid gland. Pathology indicated a low-grade adenocarcinoma. |
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Media type: CT
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| Media file 4:
Parotid, malignant tumors. Axial T1-weighted MRI with fat saturation and contrast enhancement shows an enhancing mass extending into the superficial and deep lobes of the right parotid gland. Pathology indicated a squamous cell carcinoma. |
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Media type: MRI
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| Media file 5:
Parotid, malignant tumors. Axial T2-weighted MRI shows relatively hypointense mass in the right parotid glands; this finding suggests malignancy. Pathology indicated a squamous cell carcinoma. |
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Media type: MRI
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| Media file 6:
Parotid, malignant tumors. Image shows a well-circumscribed mass in left parotid gland, which was proven to be a pleomorphic adenoma. |
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Media type: CT
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| Media file 7:
Parotid, malignant tumors. CT scan shows a carcinoma ex pleomorphic adenoma that developed after resection of the tumor (same patient as in Image 6). |
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Media type: CT
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| Media file 8:
Parotid, malignant tumors. Contrast-enhanced CT image of neck demonstrates a well-circumscribed, heterogeneously enhancing mass in the left parotid gland; this is a benign pleomorphic adenoma. |
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Media type: CT
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| Media file 9:
Parotid, malignant tumors. Axial T1-weighted MRI shows a left parotid carcinoma. |
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Media type: MRI
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| Media file 10:
Parotid, malignant tumors. Axial T2-weighted MRI shows a left parotid carcinoma. |
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Media type: MRI
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| Media file 11:
Parotid, malignant tumors. Coronal T2-weighted MRI shows a left parotid carcinoma. |
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Media type: MRI
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| Media file 12:
Parotid, malignant tumors. Axial contrast-enhanced CT scan shows an infiltrative mass involving the left parotid gland. Pathology indicated a parotid carcinoma. |
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Media type: CT
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Parotid, Malignant Tumors excerpt Article Last Updated: May 14, 2004
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