DOI:10.2214/AJR.05.1213
AJR 2007; 189:W212-W214
© American Roentgen Ray Society
Oncocytoma of the Parotid Gland: A Potential False-Positive Finding on 18F-FDG PET
Vinil N. Shah1 and
Barton F. Branstetter, IV1,2
1 Department of Radiology, University of Pittsburgh School of Medicine, 200
Lothrop St., PUH Room D-132, Pittsburgh, PA 15213.
2 Department of Otolaryngology, University of Pittsburgh School of Medicine,
Pittsburgh, PA.
Received July 13, 2005;
accepted after revision September 21, 2005.
Address correspondence to B. F. Branstetter IV
(bfb1{at}pitt.edu).
WEB
This is a Web exclusive article.
Keywords: head and neck imaging • parotid gland • PET • salivary neoplasms
Introduction
PET with 18F-FDG has been successfully used for the diagnosis,
management, and follow-up of many malignant tumors. PET is particularly useful
for staging of head and neck tumors and for detecting recurrence
[1]. Its utility in other
settings, however, such as detection of non–squamous cell cancer of the
head and neck and differentiating benign salivary gland tumors from malignant
ones, is limited [2,
3]. This lack of usefulness may
partly be explained by the poor anatomic localization of PET combined with
variable physiologic uptake of FDG in the head and neck. These factors
decrease the specificity of PET for head and neck cancer and thus increase the
rate of false-positive findings.
Combined PET/CT scanners, which fuse the functional data of PET with the
anatomic data of CT, have shown promise in the evaluation of cancer of the
head and neck [4].
Non–squamous cell cancer of the head and neck, particularly salivary
gland tumors, however, have not been studied extensively with either PET or
combined PET/CT. In cases that have been studied, the variable uptake from
salivary gland tumors often causes false-negative results
[4–6].
In addition, some benign tumors of the salivary glands, particularly Warthin's
tumor, show focal FDG uptake leading to false-positive results
[2]. These false-positive
findings reduce the utility of PET in differentiating benign salivary gland
tumors from malignant tumors. We report a case of a benign parotid oncocytoma
that had marked FDG avidity on PET/CT.
Case Report
A 76-year-old man presented with a 2-cm mass in the left side of the neck.
Fine-needle aspiration biopsy revealed adenocarcinoma, but no primary tumor
was evident on CT or physical examination. Because PET/CT has been shown to be
useful in identifying unknown primary squamous cell carcinomas, the patient
was referred for PET/CT to find the primary tumor. Imaging was performed on a
scanner (Reveal, CTI Medical Systems) that combines dualchannel CT with PET
(LSO Allegra, CTI Medical Systems). PET and contrast-enhanced CT images were
obtained from the skull base through the abdomen 1 hour after IV injection of
10 mCi of FDG. CT was used for attenuation correction and image fusion.
On PET/CT, no primary tumor was identified in the left side of the head and
neck, and there were no abnormalities outside the head and neck. A 1-cm mass,
however, was seen in the posterior aspect of the superficial lobe of the right
parotid gland (Fig. 1A,
1B). The PET portion of the
scan showed intense focal FDG uptake in the parotid lesion. The standardized
uptake value (SUV) for the lesion was 3.8, which was considered worrisome for
malignancy. However, because SUVs are not well established for
characterization of salivary gland tumors, the patient chose watchful waiting.
PET 1 month after the first scan showed no change in the size of the mass but
revealed increased activity within it, with an SUV of 6.2.
Fine-needle aspiration biopsy of the right parotid mass showed no malignant
cells; however, the aspirate was less than optimal owing to scant cellularity.
The patient agreed to excisional biopsy, and partial right parotidectomy was
performed. The pathologic specimen contained a well-circumscribed mahogany
brown lesion measuring 2.5 x 1.8 x 1.6 cm. The lesion was
homogeneous without areas of necrosis or hemorrhage. Histopathologic
examination revealed benign oncocytoma. Two months after the benign oncocytoma
was detected, a nodule palpated in the left parotid gland prompted
parotidectomy. An 8-mm primary adenocarcinoma was identified at pathologic
examination. The patient underwent definitive therapy for cancer. PET/CT and
clinical examination 4 months after treatment revealed no evidence of residual
disease.
Discussion
FDG PET has been shown in certain clinical settings to be useful in the
diagnostic evaluation and clinical management of masses of the head and neck
[7]. PET has been especially
useful in the staging and posttherapy monitoring of head and neck cancer.
Because most extracranial malignant tumors of the head and neck are squamous
cell cancer, these malignant tumors have been extensively studied regarding
the clinical applicability of PET and PET/CT
[4]. Non–squamous cell
tumors, including most salivary gland tumors, have not been studied as
extensively, and the role of PET in the diagnosis and management of such
tumors remains largely unclear.
Most salivary gland tumors arise within the parotid gland, and most of
these tumors are benign. Because therapy for these tumors is almost always
surgical, it is important for surgical planning to accurately determine
whether the tumor is benign or malignant. Physical examination, MRI,
sonography, and CT findings currently are not specific to the histopathologic
features of these tumors [5,
8,
9]. Cross-sectional imaging
techniques are generally poor for differentiating benign from malignant
parotid tumors. Characteristics such as irregular margins, infiltration into
the parenchyma, and degree of intensity on T1- and T2-weighted MR images can
be useful but are not reliable
[9]. Fine-needle aspiration
biopsy frequently does not provide enough information for diagnosis
[10]. PET also has limited
utility for differentiating benign from malignant salivary gland tumors,
primarily because of high FDG uptake by some benign salivary gland tumors,
especially Warthin's tumors
[4].
Some practitioners have used nuclear medicine techniques to evaluate
parotid gland tumors. Studies
[5,
11] have shown that of all
benign and malignant parotid gland tumors, Warthin's tumor and oncocytoma
almost exclusively accumulate 99mTc–sodium pertechnetate
after oral acid stimulation. Results in a series of 72 parotid gland tumors
[5] suggested that a
combination of salivary gland scintigraphy and PET is useful for
differentiating malignant and benign parotid tumors. In that series,
false-negative results were found in one salivary duct carcinoma (SUV, 2.01),
one mucoepidermoid carcinoma (SUV, 2.07), and one metastatic tumor of renal
cell carcinoma (SUV, 2.24). False-positive results were found in many of the
Warthin's tumors (mean SUV, 7.06), five pleomorphic adenomas, two cases of
inflammation, one basal cell adenoma, and one monomorphic adenoma.
Interestingly, the sole oncocytoma had low FDG uptake. To our knowledge, no
reports have described benign parotid oncocytoma with high FDG uptake.
Oncocytes are large, polygonal cells with granular and intensely
eosinophilic cytoplasm, a round nucleus, and a low nuclear-tocytoplasm ratio
[12]. These cells are present
in many types of human tissue, including salivary glands, thyroid, pituitary
gland, liver, kidneys, and gonads. Oncocytoma of the salivary glands is an
unusual benign tumor that appears most frequently in the parotid glands. The
clinical features resemble those of other benign and low-grade salivary gland
tumors. Surgical excision usually affords cure, but recurrences due to a
multifocal configuration or incomplete excision have been reported
[13].
Oncocytomas other than those of the salivary glands have been studied with
PET. For example, PET has been shown useful in the evaluation, treatment, and
follow-up of patients with Hürthle cell carcinoma of the thyroid gland
[12]. PET studies of patients
with Hürthle cell carcinoma have shown intense focal FDG uptake similar
to that seen in other highly metabolically active malignant tumors.
Although this case report focuses on a false-positive finding, the primary
tumor in this case, parotid adenocarcinoma, was not detected on FDG PET. This
situation is consistent with results of previous studies
[4–6]
showing variable uptake of salivary gland tumors that led to false-negative
results. This case report is the first description, to our knowledge, of a
parotid oncocytoma exhibiting intense FDG uptake on PET. This unusual case
emphasizes that PET and PET/CT by themselves may not be reliable for
classifying salivary masses as benign or malignant; both false-positive and
false-negative results may be seen.
References
- Keyes JW Jr, Watson NE Jr, Williams DW 3rd, et al. FDG PET in head
and neck cancer. AJR 1997;169
:1663
–1669[Abstract/Free Full Text]
- Branstetter BF 4th, Blodgett TM, Zimmer LA, et al. Head and neck
malignancy: is PET/CT more accurate than PET or CT alone?
Radiology 2005;235
: 580–586[Abstract/Free Full Text]
- Kitagawa Y, Nishizawa S, Sano K, et al. Whole body
18F-fluorodeoxyglucose positron emission tomography in patients with head and
neck cancer. Oral Surg Oral Med Oral Pathol2002; 93:202
–207
- Freling NJ, Molenaar WM, Vermey A, et al. Malignant parotid tumors:
clinical use of MR imaging and histologic correlation.
Radiology 1992;185
: 691–696[Abstract/Free Full Text]
- Uchida Y, Minoshima S, Kawata T, et al. Diagnostic value of FDG PET
and salivary gland scintigraphy for parotid tumors. Clin Nucl
Med 2005; 30:170
–176[CrossRef][Medline]
- Yousem DM, Kraut MA, Chalian AA. Major salivary gland imaging.
Radiology 2000;216
: 19–29[Abstract/Free Full Text]
- Wong DS, Li GK. The role of fine-needle aspiration cytology in the
management of parotid tumors: a critical clinical appraisal. Head
Neck 2000; 22:469
–473[CrossRef][Medline]
- Keyes JW Jr, Harkness BA, Greven KM, et al. Salivary gland tumors:
pretherapy evaluation with PET. Radiology1994; 192:99
–102[Abstract/Free Full Text]
- San Pedro EC, Lorberboym M, Machac J, et al. Imaging of multiple
bilateral parotid gland oncocytomas. Clin Nucl Med1995; 20:515
–518[CrossRef][Medline]
- Capone RB, Ha PK, Westra WH, et al. Oncocytic neoplasms of the
parotid gland: a 16 year institutional review. Otolaryngol Head
Neck Surg 2002; 126:657
–662[CrossRef][Medline]
- Brandwein MS, Huvos AG. Oncocytic tumors of major salivary glands.
Am J Surg Pathol 1991;15
: 514–528[Medline]
- Lowe VJ, Mullan BP, Hay ID, et al. 18F-FDG PET of patients with
Hürthle cell carcinoma. J Nucl Med2003; 44:1402
–1406[Abstract/Free Full Text]
- Bui CD, Ching AS, Carlos RC, et al. Diagnostic accuracy of
2-[fluorine-18]fluoro-2-deoxy-D-glucose positron emission tomography imaging
in nonsquamous tumors of the head and neck. J Invest
Radiol 2003; 38:593
–601
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
Top
Introduction
Case Report
