You are in: eMedicine Specialties > Radiology > HEAD AND NECK Parotid, Pleomorphic AdenomaArticle Last Updated: Apr 18, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Andrew L Wagner, MD, Assistant Professor of Radiology, Instructional Faculty, University of Virginia School of Medicine; Director of Neuroradiology, Department of Radiology, Rockingham Memorial Hospital Andrew L Wagner is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, American Society of Neuroradiology, and Radiological Society of North America Coauthor(s): Jason Haag, BS, Eastern Virginia Medical School Editors: David S Levey, MD, PhD, Musculoskeletal Radiologist, Department of Magnetic Resonance Imaging, Radsource, LLC; 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, Brown Medical School Author and Editor Disclosure Synonyms and related keywords: benign mixed tumor INTRODUCTIONSection 2 of 11
  BackgroundThe pleomorphic adenoma is by far the most common benign salivary gland tumor, accounting for as many as 80% of all such tumors. Although pleomorphic adenomas most commonly occur in the parotid gland (about 85%), this tumor may be encountered in the submandibular, lingual, and minor salivary glands as well. Although almost one half of tumors found in the minor salivary glands are malignant, the pleomorphic adenoma is still the most common tumor in these glands. PathophysiologyPleomorphic adenomas, commonly called a benign mixed tumor, are histologically composed of 2 subtypes of cells: epithelial and mesenchymal. The tumors are typically well demarcated from the surrounding tissue by a fibrous capsule, which varies both in thickness and completeness. These lesions have been reported to contain small protrusions (pseudopodia) that extend beyond the central mass, caused by variability in the growth rates of the various cell types. This factor contributes to recurrence rates as high as 50%, depending on the type of surgical intervention. Hemorrhage, calcification, and necrosis are occasionally present. Most pleomorphic adenomas are confined to the superficial lobe of the parotid gland, but they can occasionally arise in the deep lobe in other salivary glands. Malignant degeneration, most commonly carcinoma ex pleomorphic adenoma, has been reported to occur in as many as 25% of untreated cases. In rare cases, pleomorphic adenomas degenerate into a true malignant mixed tumor and a metastasizing benign mixed tumor. FrequencyUnited StatesPleomorphic adenomas account for as many as 80% of all benign salivary tumors. Mortality/MorbidityThe morbidity and mortality of pleomorphic adenomas can be divided into 3 main categories: carcinoma, local recurrence after surgery, and facial nerve injury.
RaceWhite persons have a slightly higher risk of pleomorphic adenomas than that of other races. SexWomen are predominantly affected, with a female-to-male ratio of 3:2. AgePleomorphic adenoma typically appears in between the fourth and sixth decades of life and is rare in children. The average patient age at presentation is 43 years. AnatomyThe parotid gland is the largest of the salivary glands. It arises as an epithelial invagination in the lining of the oral cavity at about 5 weeks' gestation. The parotid gland is located anteroinferior to the external acoustic meatus wedged between the ramus of the mandible anteriorly and the mastoid process posteriorly. Its apex is found posterior to the angle of the mandible, and its base is found slightly inferior to the zygomatic arch. The gland is divided into a larger superficial lobe and smaller deep lobe by the facial nerve, which enters the posterior parotid, branches and then exits the gland anteriorly. Adjacent to but slightly deeper to the facial nerve is the retromandibular vein, followed by the external carotid artery, both of which have a number of branches within the gland. The retromandibular vein, which drains into the external jugular vein, roughly parallels the course of the facial nerve. Therefore, this vein can be used as guide to determine the location of the nerve on imaging studies. The parotid gland itself is enclosed by a tough fascial capsule, the parotid sheath, which is derived from the deep cervical fascia. Innervation of the parotid gland includes both parasympathetic fibers from the glossopharyngeal nerve and sympathetic innervation via the external carotid nerve plexus. Histologically, the gland is composed primarily of acinar cells, and upon stimulation, they produce a watery, serous solution, which is excreted by the parotid (Stensen) duct. This duct exits the anteromedial portion of the gland, crosses the masseter superficially, pierces the buccinator, and enters the oral cavity opposite the second maxillary molar. In addition to parotid tissue, parotid glands typically have lymph nodes that may or may not be visible on imaging. Clinical DetailsParotid pleomorphic adenomas typically arise as a slow-growing, firm parotid mass that is slightly compressible. Almost all are asymptomatic, and they are usually brought to the attention of the physician when routine physical examination is performed or when the patient feels or sees a parotid mass. Typically, the signs and symptoms have been present for at least a year before patients seek medical attention. Preferred ExaminationCT or MRI depicts the mass, and the findings may be essentially diagnostic in routine cases with typical features. Some authors have reported excellent sensitivity with ultrasonography, though this study typically does not help the surgeon to understand the 3-dimensional (3D) relationship of the tumor to the parotid gland and the facial nerve. Limitations of TechniquesMRI has the advantages of multiplanar imaging, and MRI results may suggest the tissue type on the basis of signal intensity characteristics. CT is often the first study ordered in patients with neck masses, and scans can show the mass and the retromandibular vein. Newer multisection CT scanners offer multiplanar capabilities rivaling that of MRI. Disadvantages of CT include radiation exposure, the use of iodinated contrast material, and tissue distinction poorer than that of other studies. CT may also be problematic in cases of benign pleomorphic adenomas when the outer margin of the tumor appears indistinct and suggests malignant invasion of the surrounding tissue. MRIs show the well-defined outer borders in these instances. In many cases, however, CT may be the only study needed to guide the surgeon. DIFFERENTIALSSection 3 of 11
Parotid, Malignant Tumors Other Problems to Be ConsideredWarthin tumor
RADIOGRAPHSection 4 of 11
FindingsSialography has been used in the past to diagnose parotid tumors, but it has been abandoned with the advent of CT and MRI. Pleomorphic adenomas appear as smoothly marginated masses that displace the parotid tissue and ducts. False Positives/NegativesMany parotid tumors and lymph nodes can have a similar appearance. CT SCANSection 5 of 11
FindingsPleomorphic adenomas are typically smooth, well-marginated tumors, though nodularity along the outer surface is sometimes present. The attenuation values of the mass are usually homogeneous and higher than that of the surrounding gland, though lower attenuation masses that resemble cysts are occasionally seen. Tumor enhancement is variable and can result in a missed diagnosis if delayed images are not acquired. Pleomorphic adenomas are poorly enhancing in the early phase of contrast enhancement, though the amount of enhancement increases over time. Delayed images obtained at 5-10 minutes are often useful. Lev et al described increased degree and homogeneity of tumor enhancement over time. Although the average delay was 24 minutes, in practice, a 5- to 10-minute delay is almost as effective. When pleomorphic adenomas become large, they may develop a heterogeneous appearance with areas of necrosis, hemorrhage, cysts, and calcification. Large tumors commonly have a lobulated contour, which strongly suggests the diagnosis. Degree of ConfidenceAlthough certain CT features (eg, lobulation, homogeneity, delayed contrast enhancement) can suggest the diagnosis of pleomorphic adenoma, these findings are not specific to the tumor. In addition, CT results may falsely suggest invasion of the surrounding tissue; in these cases, MRI should be performed to ensure that a diagnosis of malignancy is not incorrectly made. MRIs can demonstrate a well-defined capsule, even when the border appears irregular on CT scans. MRISection 6 of 11
FindingsPleomorphic adenomas are usually well-circumscribed, homogeneous masses with low intensity on T1-weighted images and high intensity on T2-weighted images. They commonly have a rim of decreased signal intensity on T2-weighted images; this rim also appears hypointense on fat-suppressed T1-weighted images. This finding represents the surrounding fibrous capsule. A well-defined parotid mass with increased signal intensity on proton density- and T2-weighted images is highly suggestive of the diagnosis. In fact, the increased signal intensity on T2-weighted images is so prevalent that any parotid mass with this finding should be viewed with suspicion, as this often indicates a carcinoma ex pleomorphic adenoma. When it becomes large, the tumor may lose its homogeneous appearance on MRI, as with CT. It may have areas of fibrosis, necrosis, and hemorrhage. Inhomogeneous signal intensity should be apparent in these cases. Lobulation is commonly visualized and is, in itself, also suggestive of the diagnosis. After gadolinium enhancement, the tumors are homogeneously enhancing unless they are large. Unlike CT, MRI has no role in delayed imaging. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble movingor straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. Degree of ConfidenceThe diagnosis of pleomorphic adenoma can be at least strongly suggested in most cases. Special attention should be paid to the signal intensity of the tumor and to any possible invasion into adjacent soft tissues. ULTRASOUNDSection 7 of 11
FindingsOn sonograms, pleomorphic adenomas typically appear as smooth, round, hypoechoic masses with distal acoustical enhancement. Lobulations are commonly visualized. Large tumors appear more heterogeneous than small ones and are better imaged with CT or MRI than with sonography. Degree of ConfidenceAlthough sonographic findings can suggest the diagnosis of pleomorphic adenoma in many small tumors, CT or MRI is needed to fully evaluate large tumors. Even in patients in whom the diagnosis is made by means of sonography and biopsy, CT or MRI is needed for preoperative planning. NUCLEAR MEDICINESection 8 of 11
Degree of ConfidenceEvidence suggests that dual-isotope imaging with technetium Tc 99m and thallium Tl 201 single-photon emission CT (SPECT) is accurate in distinguishing various tumors of the salivary glands, including pleomorphic adenomas. INTERVENTIONSection 9 of 11
The current standard is that all pleomorphic adenomas should be surgically removed because the risk of malignancy is 25% if the tumors are left untreated. MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Parotid, Pleomorphic Adenoma excerpt Article Last Updated: Apr 18, 2007 | |||||||||||||||||||||||||||||||||||
