Keywords
parotid gland - adenolymphoma - PET scan - cigarette smoking
Introduction
It is not unusual to find unexpected hypermetabolic foci as a result of scanning using
whole-body positron emission/computed tomography (PET/CT). Known as incidentalomas, such findings are not necessarily related to the tumor or disease being studied.
Parotid gland incidentalomas (PGIs) are defined as new focal intraglandular deposits
of radiotracer in patients without prior history of parotid disease.[1] These deposits are most commonly due to benign lesions such as Warthin tumor (WT),[1]
[2]
[3]
[4]
[5] but they can also be caused by metastatic lymph nodes or malignant tumors.[6]
The parotid gland is the salivary gland that most commonly develops tumors, most of
which are benign. After pleomorphic adenoma, WT is the second most prevalent parotid
tumor. It presents as a slow-growing mass in the tail of the gland, and is usually
asymptomatic. It generally occurs between the sixth and seventh decades of life, predominantly
in men. It has a strong association with smoking, which is therefore considered a
risk factor for its development.[7]
[8]
[9]
[10] WT can be multicentric or bilateral, and it rarely becomes malignant.
To our knowledge, only two previous studies have reported the prevalence of PGI, and
both were performed in Asia.[2]
[11] Furthermore, clinical features such as the role of smoking have not been considered
in their etiology. The present study aimed to determine the prevalence of parotid
incidentalomas in 18F-fluorodeoxyglucose (18F-FDG) PET/CT and evaluate the presence of smoking in this group of patients. We also
reviewed the database of parotidectomies performed in our hospital to assess the relationship
between WT and smoking.
Materials and Methods
Patients
We conducted a retrospective review of the reports of PET/CT performed in 4,250 patients
in our hospital between June 2009 and February 2013. We identified 16 cases of parotid
focal uptake in patients without known disease of the parotid glands. The group consisted
of 10 men and 6 women, 48 to 88 years of age. In most cases, PET-CT was indicated
as an extension study of diagnosed neoplasms or to confirm locoregional relapse after
treatment. In two cases, it was indicated to rule out giant cell arteritis.
We reviewed the history of smoking in the 16 cases: 13 had smoked or were current
smokers. We identified additional studies performed on the parotid masses, finding
that only 5 patients underwent cytologic analysis by fine needle aspiration cytology
(FNAC). In 8 of the 16 cases, the lesion was located in the right parotid gland, in
7 cases it was located on the left, and in 1 case it was bilateral. Two patients had
more than one deposit within the same gland.
We analyzed the database of parotidectomies performed in our department in the previous
10 years and focused on the pathologic diagnosis and the presence or absence of smoking
in each case.
18F-Fluorodeoxyglucose Positron Emission/Computed Tomography
Combined 18F-FDG whole-body PET/CT (Gemini TF, Philips, Amesterdam) with 64-slice CT was performed.
Standard patient preparation included: 6-hour fasting, hydration, and serum glucose
level of less than 150 mg/dL before tracer injection. Patients were asked to rest
quietly in supine position, and vesical evacuation was done before the acquisition
of images.
A dose of 3.7 MBq/kg of 18F-FDG was intravenously injected. Low-dose CT and PET from the base of the skull to
the proximal thighs were performed, with an additional acquisition of head and neck
images. The total examination time was ∼20 minutes. An abnormal PET-CT finding was
defined as a significant increased uptake, higher than that of the surrounding normal
tissue.
Results
We found PGIs in 16 patients who underwent PET/CT between June 2009 and February 2013,
corresponding to 0.4% of patients undergoing PET/CT. The incidentalomas were more
frequent in men (62.5%, 10 cases), and the average age at diagnosis was 68 years.
The most common indication for the test was lung cancer (7 cases, corresponding to
43.75%), followed by breast cancer (3 cases), giant cell vasculitis (1 case each of
Horton disease and Takayasu arteritis), and 1 case each of locally advanced oropharyngeal
cancer, gallbladder carcinoma with liver metastasis, peritoneal carcinomatosis of
gynecologic origin, and retroperitoneal lymphoma. (See [Table 1.])
Table1
Data of 16 patients with parotid incidentalomas detected by PET/CT
|
Patient
|
Age (y)
|
Sex
|
Smoking
|
SUVmax
|
Cytology (FNAC)*
|
PET/CT indication
|
|
1
|
64
|
Male
|
Yes
|
4.3 and 3
|
Negative for malignancy
|
Lung cancer
|
|
2
|
48
|
Female
|
Yes
|
16.1
|
Negative for malignancy
|
Horton disease
|
|
3
|
64
|
Female
|
No
|
5.1
|
Not performed
|
Breast cancer
|
|
4
|
66
|
Female
|
No
|
4.55
|
Not performed
|
Breast cancer
|
|
5
|
71
|
Male
|
Yes
|
4.03
|
Inconclusive cytology
|
Gallbladder cancer
|
|
6
|
88
|
Female
|
Yes
|
3.3
|
Negative for malignancy
|
Peritoneal carcinomatosis
|
|
7
|
54
|
Male
|
Yes
|
5.5
|
Not performed
|
Lung cancer
|
|
8
|
74
|
Male
|
Yes
|
2.87
|
Not performed
|
Lung cancer
|
|
9
|
79
|
Female
|
No
|
5.5
|
Pleomorphic adenoma
|
Breast cancer
|
|
10
|
81
|
Male
|
Yes
|
4
|
Not performed
|
Retroperitoneal lymphoma
|
|
11
|
63
|
Male
|
Yes
|
15.9
|
Not performed
|
Lung cancer
|
|
12
|
65
|
Male
|
Yes
|
3.5
|
Not performed
|
Oropharyngeal cancer
|
|
13
|
85
|
Male
|
Yes
|
13.1 and 9.9
|
Not performed
|
Lung cancer
|
|
14
|
58
|
Female
|
Yes
|
6.8
|
Not performed
|
Takayasu arteritis
|
|
15
|
65
|
Male
|
Yes
|
5.5
|
Not performed
|
Lung cancer
|
|
16
|
70
|
Male
|
Yes
|
4.29
|
Not performed
|
Lung cancer
|
Abbreviations: FNAC, fine needle aspiration cytology; PET/CT; positron emission/computed
tomography; SUVmax, standardized uptake value.
Five of the 16 patients underwent FNAC of the parotid mass. Three of five masses had
an inflammatory component without a malignant component, one was considered a mixed
tumor suggestive of pleomorphic adenoma, and the other was inconclusive. Of the 16
patients, only the patient with the pleomorphic adenoma underwent surgery; a superficial
parotidectomy was performed and the histology was confirmed. In the remaining 11 cases,
FNAC was not performed but the mass was monitored by periodic clinical follow-up.
Thirteen patients (81.25%) had a history of smoking. One of the three nonsmokers was
the patient with the pleomorphic adenoma.
The average standardized uptake value of parotid tumors was 6.51, ranging from 2.87
to 16.1. The term used to describe the lesions was hyperintense or hypermetabolic intraglandular nodule.
A review of the database of parotidectomies performed in our department revealed that
311 patients were surgically treated for parotid gland tumors in the previous 10 years
and 80 cases (25.7%) were identified as WT. This was the second most frequent tumor
after pleomorphic adenoma. A history of smoking was identified in 93.8% of patients
with WT (75 cases). This percentage was high compared with the prevalence of smoking
in pleomorphic adenomas, which was 38.8%. (See [Table 2.])
Table 2
Data of parotidectomies performed in our department in the previous 10 years
|
Histologic diagnosis
|
Number of cases (%)
|
Smoking status (%)
|
|
Pleomorphic adenoma
|
134 (43.1%)
|
52 (38.8%)
|
|
Warthin tumor
|
80 (25.7%)
|
75 (93.8%)
|
|
Malignant tumors
|
56 (18%)
|
31 (55.4%)
|
|
Other diagnosis
|
41 (13.2%)
|
17 (41.5%)
|
|
Total
|
311 (100%)
|
175 (56.3%)
|
Discussion
Our findings show that the prevalence of PGIs on PET/CT in our institution is similar
to that reported in the two previous studies in Asia. When analyzing the presence
of cigarette smoking in our patients with PGIs, we found it was a common factor in
81.25% of the patients.
In our study, FNAC was performed in five cases. Three were negative for malignancy
without typing the lesion. One case was a pleomorphic adenoma and the other had a
nondiagnostic smear. The remaining patients did not undergo additional testing on
the PGI due to the advanced stage of the primary tumor, the absence of symptoms, or
the unlikelihood of metastasis based on clinical and tomographic features.
In the largest series published to date, Wang et al found 58 PGIs in 19,333 patients,
representing a prevalence of 0.3%.[11] They obtained histologic confirmation in 51 patients, 41 with benign lesions (mainly
represented by pleomorphic adenomas and WT) and 10 with malignant tumors. In a smaller
sample, Horiuchi et al detected four cases of abnormal parotid FDG uptake in 1,872
PET scans, with an estimated prevalence of 0.2%; all four cases were diagnosed with
WT.[2] Other series of cases also found WT as the main cause of PGI.[1]
[3]
As PGIs are likely benign lesions, metastasic disease should not be suspected initially
without histopathologic confirmation, even in patients with known malignancy elsewhere.[1]
[4]
[5] Nevertheless, these lesions warrant further radiologic and histopathologic correlations.
Ultrasonography and FNAC are useful tools to characterize parotid masses, avoiding
erroneous staging of primary malignancies. The objective of cytologic diagnosis of
parotid masses is the differential diagnosis between benign and malignant lesions.[12] Complex histopathology and heterogeneity of cellular patterns of salivary gland
tumors explain why typing of primary salivary malignancies by FNAC is a challenge.
The accuracy of FNAC depends on the experience of the clinician who performs the procedure
and the pathologist who evaluates cytologic material.[12]
We found the prevalence of smoking in parotid tumors surgically treated in our hospital
was significantly higher in patients with WT than in patients with other tumors (p < 0.001). More than 90% of patients with WT were smokers, and cigarette use in patients
with other benign and malignant neoplasms was lower, 38 and 55.4%, respectively. Several
other authors have studied the relation between WT and smoking. According to their
publications, between 80 and 94% of patients with WT smoke,[7]
[8]
[9]
[13] and the risk for development of WT correlates with the level and duration of smoking.[7]
[9] Sadetzki et al found a remarkably high odds ratio (15.3) for developing WT in the
presence of smoking.[9]
Conclusion
Based on the high prevalence of WT as PGI on PET/CT and the strong relationship with
smoking, we suggest diagnosis other than Warthin tumor should be considered for PGI
in nonsmokers. Further studies with histologic diagnosis and larger samples are warranted
to confirm our hypothesis.
