Significance of incidental fluorodeoxyglucose uptake in the parotid glands and its impact on patient management

Cancer in Patients With Incidental Asymmetric Oropharynx Positron Emission Tomography Uptake

Importance

Asymmetric oropharynx uptake on positron emission tomography (PET)/computed tomography (CT) is a common incidental finding and often prompts otolaryngology referral to rule out malignancy; however, the true risk of malignancy based on this finding is unknown.

Objective

To identify the incidence of oropharynx cancer in patients with incidental asymmetric oropharynx PET uptake.

Design, Setting, and Participants

In this retrospective cohort study, patients 18 years and older undergoing PET/CT scans at Mayo Clinic between January 2001 and December 2018 were included. Patients with a history or pretest suspicion of oropharynx cancer were excluded. Data were analyzed from March 2021 to December 2023.

Exposure

Blinded radiologic review of imaging studies, including measurement of maximum standardized uptake values (SUVmax) of the ipsilateral side of concern and contralateral side. Retrospective medical record review for associated clinical data.

Main Outcomes and Measures

The primary study outcome was the incidence of oropharynx cancer diagnosis in patients with asymmetric oropharynx PET uptake. The primary outcome was formulated before data collection.

Results

Of the 1854 patients identified with asymmetric oropharynx PET uptake, 327 (17.6%) met inclusion criteria. Of these, 173 (52.9%) were male, and the median (range) age was 65.0 (24.8-90.7) years. The mean (SD) follow-up interval was 52.1 (43.4) months. A total of 18 of 327 patients (5.5%) were newly diagnosed with oropharynx cancer. The most common diagnosis was squamous cell carcinoma (n = 9), followed by lymphoma (n = 8), and sarcoma (n = 1). Patients with an incidental diagnosis of oropharynx cancer had higher mean (SD) ipsilateral SUVmax (8.7 [3.7] vs 5.3 [1.9]) and SUVmax ratio (3.0 [1.6] vs 1.6 [0.6]) compared with patients with normal examination findings. SUVmax ratio and difference were found to be good discriminators of oropharynx cancer, with areas under the receiver operating characteristic curve of 86.3% (95% CI, 76.4-94.6) and 85.8% (95% CI, 74.8-94.6), respectively. Patients with a new diagnosis of oropharynx cancer were more likely to have a corresponding CT abnormality than those with normal examination findings (6 of 18 [33%] vs 24 of 295 [8.1%]). Patients with concerning lesions on oropharynx palpation by an otolaryngology health care professional were significantly more likely to be diagnosed with oropharynx cancer compared with patients with normal examination findings (odds ratio, 28.4; 95% CI, 6.6-145.8).

Conclusions and Relevance

In this cohort study, while incidental asymmetric oropharynx PET uptake was common, a new diagnosis of oropharynx cancer was not and potentially results in a large volume of unnecessary referrals and work-up. Using SUVmax ratio, SUVmax difference, and CT correlation may increase the benefit of referral. Patients with a palpable oropharynx lesion and asymmetric oropharynx PET uptake should undergo confirmatory biopsy.

Fine needle aspiration diagnosis of benign oncocytic lesions of the head and neck associated with false positive 18F-fluorodeoxyglucose uptake on positron emission tomography scan

INTRODUCTION

18F-fluorodeoxyglucose (FDG) uptake on positron emission tomography/computed tomography (PET/CT) has become the mainstay for staging and post-therapy surveillance of cancer as malignant neoplasms generally demonstrate higher FDG uptake that benign entities. However, there are certain benign lesions, most notably oncocytic tumors, that can display very high uptake and fine needle aspiration (FNA) is usually done to confirm malignancy. Therefore, it is important to recognize that benign oncocytic lesions of the head and neck may also present as FDG-avid lesions to avoid a diagnostic pitfall.

METHODS

Electronic search of institutional surgical and cytopathology archives was conducted to identify cases of benign oncocytic lesions involving the head and neck region diagnosed by FNA from January 2012 to April 2022. Chart review was used to assess whether lesions were initially discovered via PET scanning.

RESULTS

One hundred and twenty-five cases of oncocytic lesions were identified; 12 (9%) PET positive lesions were identified in the head and neck region from patients being evaluated for metastasis or for suspicion of malignancy. Cytopathology of all 12 cases demonstrated benign oncocytic lesions; eight (67%) of these cases were consistent with Warthin tumor, one (8.3%) was a benign oncocytic lesion, and one (8.3%) was consistent wit a parathyroid adenoma. Most (58%) of the PET-positive lesions were in parotid region, two from thyroid gland (17%), one from submandibular gland (8%), one from paratracheal area (8%). The PET scan SUVs ranged from 3.3 to 19.5 g mL-1.

CONCLUSIONS

Oncocytic lesions including Warthin tumors can result in false-positive FDG uptake on PET scans. Clinicians and cytopathologists should be aware of PET-positive benign oncocytic head and neck lesions.

Incidental [18F]FDG-avid focuses in parotid glands on PET/CT

BACKGROUND

The number of unexpected focal [18F]FDG-avid findings (incidentalomas) within the parotid gland (PGI) continues to increase with the expanding use of PET/CT scanning. The prevalence of malignancy in PGIs is uncertain and appropriate management is unsettled.

AIMS

We aimed to explore the underlying pathologies associated with PGI.

MATERIALS AND METHODS

A retrospective review of all patients with parotid gland incidentaloma(s) treated at the Ear-Nose-Throat Department, Aarhus University Hospital, Denmark in the period 2012-2021, was performed.

RESULTS

In total, 94 patients with one (n = 86) or two (n = 8) PGI(s) were included. In patients with one PGI, 72 (84%) focuses were benign, two (2%) focuses were malignant (both malignant melanoma metastases), and 12 (14%) focuses were undiagnosed. In patients with two PGIs, all 12 lesions with pathological examinations were benign (4 PGIs were undiagnosed). The median SUVmax found in benign lesions was higher (12.0) compared to malignant lesions (5.5) (p = .043).

CONCLUSIONS AND SIGNIFICANCE

The prevalence of malignancy was low (2/94, 2.4%) in PGIs. Based on our findings, PGI in patients without a history of parotid malignancy, who undergo PET/CT scanning for reasons other than head and neck cancer (including malignant melanoma), may be managed similarly to patients with asymptomatic parotid gland tumors.

Prevalence and Clinical Implications of Incidentally Detected Parotid Lesions as Blind Spot on Brain MRI: A Single-Center Experience

Background and objective: This study was conducted to assess the prevalence and clinical implications of parotid lesions detected incidentally during brain magnetic resonance imaging (MRI) examination. Materials and Methods: Between February 2016 and February 2021, we identified 86 lesions in the brain MRI reports of 84 patients that contained the words “parotid gland” or “PG”. Of these, we finally included 49 lesions involving 45 patients following histopathological confirmation. Results: Based on the laboratory, radiological or histopathological findings, the prevalence of incidental parotid lesions was low (1.2%). Among the 45 study patients, 41 (91.1%) had unilateral lesions, and the majority of the lesions were located in the superficial lobe (40/49, 81.6%). The mean size of the parotid lesions was 1.3 cm ± 0.4 cm (range, 0.5 cm–2.8 cm). Of these, 46 parotid lesions (93.9%) were benign, whereas the remaining three lesions were malignant (6.1%). Conclusions: Despite the low prevalence and incidence of malignancy associated with incidental parotid lesions detected on brain MRI, the clinical implications are potentially significant. Therefore, clinical awareness and appropriate imaging work-up of these lesions are important for accurate diagnosis and timely management.

Parotid incidentalomas: a systematic review

OBJECTIVE

Parotid incidentalomas on fluorodeoxyglucose positron emission tomography/computed tomography imaging are rare. A systematic review was performed to assess their aetiology and association with scanning indication, and to develop an evidence-based algorithm for their management.

METHODS

A literature search was performed on 25 August 2020 using the keywords 'incidentaloma', 'incidental finding', 'parotid', 'parotid gland', 'salivary gland' and 'head and neck'. Articles were reviewed by two authors before their inclusion.

RESULTS

Forty articles were included, totalling 558 incidentalomas. The mean incidence was 0.74 per cent. Lung cancer was the most common imaging indication. The most common aetiologies were cystadenolymphoma, pleomorphic salivary adenoma and metastases. Only cystadenolymphoma (p = 0.015) and pleomorphic salivary adenoma (p = 0.011) were significantly associated with a primary malignancy (lung). The most common further investigations were aspiration cytology, ultrasound imaging and core biopsy, usually prior to parotidectomy.

CONCLUSION

If appropriate, parotid incidentalomas should be followed up with flexible endoscopy, skin examinations, and head and neck examinations. Ultrasound-guided core biopsy provides higher accuracy, avoiding repeat sampling and excision biopsy.

Observation Rather than Surgery for Benign Parotid Tumors: Why, When, and How

Surgery is the preferred treatment of benign parotid lesions, but it carries a risk of complications. Therefore, the approach toward the surgery of these lesions should seek to avoid complications. There are no guidelines or recommendations for when not to operate. Integration of comorbidities and other factors shift the scales from surgery toward observation in a small subset of patients presenting with parotid tumors. When observation is chosen, the patient should be followed frequently and cautiously, and the surgeon should be prepared to change strategy to surgical excision if in doubt.

Advanced imaging for quantification of abnormalities in the salivary glands of patients with primary Sjögren's syndrome

Objectives

To assess non-invasive imaging for detection and quantification of gland structure, inflammation and function in patients with primary Sjogren's syndrome (pSS) using PET-CT with ¹¹C-Methionine (¹¹C-MET; radiolabelled amino acid), and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG; glucose uptake marker), to assess protein synthesis and inflammation, respectively; multiparametric MRI evaluated salivary gland structural and physiological changes.

Methods

In this imaging/clinical/histology comparative study (GSK study 203818; NCT02899377) patients with pSS and age- and sex-matched healthy volunteers underwent MRI of the salivary glands and ¹¹C-MET PET-CT. Patients also underwent ¹⁸F-FDG PET-CT and labial salivary gland biopsies. Clinical and biomarker assessments were performed. Primary endpoints were semi-quantitative parameters of ¹¹C-MET and ¹⁸F-FDG uptake in submandibular and parotid salivary glands and quantitative MRI measures of structure and inflammation. Clinical and minor salivary gland histological parameter correlations were explored.

Results

Twelve patients with pSS and 13 healthy volunteers were included. Lower ¹¹C-MET uptake in parotid, submandibular and lacrimal glands, lower submandibular gland volume, higher MRI fat fraction, and lower pure diffusion in parotid and submandibular glands were observed in patients vs healthy volunteer, consistent with reduced synthetic function. Disease duration correlated positively with fat fraction and negatively with ¹¹C-MET and ¹⁸F-FDG uptake, consistent with impaired function, inflammation and fatty replacement over time. Lacrimal gland ¹¹C-MET uptake positively correlated with tear flow in patients, and parotid gland ¹⁸F-FDG uptake positively correlated with salivary gland CD20+ B-cell infiltration.

Conclusion

Molecular imaging and MRI may be useful tools to non-invasively assess loss of glandular function, increased glandular inflammation and fat accumulation in pSS.

PET/CT Variants and Pitfalls in Head and Neck Cancers Including Thyroid Cancer

PET/CT imaging is a dual-modality diagnostic technology that merges metabolic and structural imaging. There are several currently available radiotracers, but ¹⁸F-FDG is the most commonly utilized due to its widespread availability. ¹⁸F-FDG PET/CT is a cornerstone of head and neck squamous cell carcinoma imaging. ⁶⁸Ga-DOTA-TOC is another widely used radiotracer. It allows for whole-body imaging of cellular somatostatin receptors, commonly expressed by neuroendocrine tumors and is the standard of reference for the characterization and staging of neuroendocrine tumors. The normal biodistribution of these PET radiotracers as well as the technical aspects of image acquisition and inadequate patient preparation affect the quality of PET/CT imaging. In addition, normal variants, artifacts and incidental findings may impede accurate image interpretation and can potentially lead to misdiagnosis. In order to correctly interpret PET/CT imaging, it is necessary to have a comprehensive knowledge of the normal anatomy of the head and neck and to be cognizant of potential imaging pitfalls. The interpreter must be familiar with benign conditions which may accumulate radiotracer potentially mimicking neoplastic processes and also be aware of malignancies which can demonstrate low radiotracer uptake. Appropriate use of structural imaging with either CT, MR or ultrasound can serve a complimentary role in several head and neck pathologies including local tumor staging, detection of bone marrow involvement or perineural spread, and classification of thyroid nodules. It is important to be aware of the role of these complementary modalities to maximize diagnostic accuracy and patient outcomes. The purpose of this article is to outline the basic principles of PET/CT imaging, with a focus on ¹⁸F-FDG PET/CT and ⁶⁸Ga-DOTA PET/CT. Basic physiology, variant imaging appearances and potential pitfalls of image interpretation are presented within the context of common use cases of PET technology in patients with head and neck cancers and other pathologies, benign and malignant.

Clinicopathological features of incidental parotid lesions

Background

The purpose of this study is to determine the histopathological spectrum and risk of primary malignancy of asymptomatic parotid lesions incidentally discovered on cross-sectional imaging.

Methods

Over a 10-year period, 154 patients underwent 163 ultrasound-guided parotid lesion biopsies at our institution. This retrospective chart review included 89 lesions in 87 patients with asymptomatic parotid lesions discovered on cross-sectional imaging studies performed for unrelated clinical indications. The histopathologic findings of all sampled lesions were reviewed. We evaluated the patient demographics and pathological diagnoses of sampled parotid lesions to determine the histopathological spectrum and risk of malignancy.

Results

The average age was 67.5 years and 92 % were males. 25 % of patients had bilateral lesions. The average size of the parotid lesions was 1.5 cm and 91 % were located in the superficial lobe. 92.1 % of lesions were benign with Warthin tumor being the most common diagnosis followed by pleomorphic adenoma. 2.3 % of lesions were primary parotid malignant neoplasms, while 5.6 % were metastatic lesions in patients with known malignancy.

Conclusions

The incidence of primary parotid malignant neoplasm in asymptomatic incidentally discovered parotid lesions is low. Imaging or clinical follow-up may be considered in patients with incidental parotid lesions who prefer to avoid biopsy.

The Clinical Significance of Incidental Parotid Uptake in a PET/CT Study: A Diagnostic Algorithm

BACKGROUND

Patients diagnosed with cancer do not have sufficient clinical data for the management of incidental parotid lesions. We aimed to reveal the importance of randomized parotid lesions encountered during oncologic F-18 fluorodeoxyglucose positron emission tomography (FDG PET/CT) imaging in our clinical practice and the diagnostic algorithm of such lesions.

METHODS

We performed a database search of PET/CT records generated from 2009 to 2015 for "parotid" in reports of patients who underwent PET/CT examination for a known malignancy elsewhere, or cancer screening.

RESULTS

Incidental parotid FDG uptake on PET/CT had a prevalence of 1.1%. The incidence of parotid metastasis in our series was 36.4%, and 75% of them had malign melanoma metastasis. Of the 11 cases, 5 were of Warthin tumours, and Warthin tumours showed stronger GLUT1 expression than metastatic parotid lesions.

CONCLUSION

In patients with malignancy elsewhere, focal involvement of FDG by the parotid gland, especially if malignant melanoma or SCC is absent, should not be considered a metastatic disease without histopathologic confirmation. If parotid disease would change the patient's treatment plan and disease stage, the parotid lesion should be evaluated by additional methods, such as fine needle aspiration biopsy.

Fibroblast Activation Protein-Targeted PET/CT with 68Ga-FAPI for Imaging IgG4-Related Disease: Comparison to 18F-FDG PET/CT

IgG4-related disease (RD) is characterized by lymphoplasmacytic infiltration enriched in IgG4-positive plasma cells and variable degrees of fibrosis with a characteristic storiform pattern. Since fibrosis is an important feature of IgG4-RD, we performed a prospective cohort study to evaluate the performance of ⁶⁸Ga-fibroblast activation protein inhibitor (FAPI), a recently introduced PET agent targeting fibroblast activation protein, in IgG4-RD. Methods: Twenty-six patients with IgG4-RD were recruited. All patients underwent both ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT. The positive rates of the PET/CT scans in the involved organs and the uptake values were compared. Results: In a total of 136 involved organs in the 26 patients, ⁶⁸Ga-FAPI PET/CT additionally detected 18 (13.2%) involved organs in 13 (50.0%) patients, compared with ¹⁸F-FDG PET/CT. ⁶⁸Ga-FAPI PET/CT had a higher positive rate than ¹⁸F-FDG PET/CT in detecting involvement in the pancreas, bile duct/liver, and lacrimal gland. ⁶⁸Ga-FAPI also demonstrated significantly higher uptake than ¹⁸F-FDG in the matched disease in the pancreas, bile duct/liver, and salivary gland (P < 0.01). However, lymph node involvement with flip-flop uptake of ¹⁸F-FDG did not accumulate ⁶⁸Ga-FAPI. Conclusion: ⁶⁸Ga-FAPI might be a promising imaging agent for the assessment of IgG4-RD.

Incidence of Non-Salivary Gland Neoplasms in Patients with Warthin Tumor: A Study of 73 Cases

Warthin tumor is the second most common benign parotid neoplasm. Its association with non-salivary gland neoplasms has been sporadically reported. We reviewed clinical records of Warthin tumor diagnosed on aspiration cytology and surgical pathology to determine if there is any association with other extra-salivary gland malignant neoplasms. Computer search was made for all cases of Warthin tumor diagnosed in the parotid gland by aspiration cytology and surgical pathology at our institution between January 2007 and August 2016. Clinical records of all cases were reviewed for any associated malignant neoplasms and any surgical follow up. All available cytology and histologic material was reviewed. Seventy-three patients (mean 66.9, M:F 1.1:1, age range 43 to 87 years) with Warthin tumor were identified. 45 (62%) were diagnosed on aspiration cytology only, 19 (26%) had cytologic diagnosis as well as concordant surgical follow up, and 9 (12%) were diagnosed based on surgical pathology only. Average age for patients with and without secondary malignancy was 70.5-years, and 63.4-years, respectively (p < 0.05). Average pack years for patients with and without secondary malignancy was 45.4, and 39.8, respectively (p > 0.05). Twenty-seven (37.0%) patients harbored a malignant neoplasm. Association of extra salivary gland malignant neoplasms in 37.0% of our cases suggest that the prevalence of secondary non-salivary neoplasms in patients harboring Warthin tumor might have been underestimated. Squamous cell carcinoma was the most commonly associated non-salivary malignant neoplasm. The association of Warthin tumor with smoking plays an important role in this increased rate of malignancy, and this is supported by the fact that smoking is highly associated with head and neck and lung cancers.

Thyroid Incidentalomas on 18F-FDG PET/CT: Clinical Significance and Controversies

OBJECTIVE

The purpose of the current study is to examine the incidence and clinical significance of unexpected focal uptake of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) on positron emission tomography/computed tomography (PET/CT) in the thyroid gland of oncology patients, the maximum standardized uptake value (SUV_max) of benign and malignant thyroid incidentalomas in these patients, and review the literature.

METHODS

Seven thousand two hundred fifty-two ¹⁸F-FDG PET/CT studies performed over four years, were retrospectively reviewed. Studies with incidental focal ¹⁸F-FDG uptake in the thyroid gland were further analyzed.

RESULTS

Incidental focal thyroid ¹⁸F-FDG uptake was identified in 157 of 7252 patients (2.2%). Sufficient follow-up data (≥12 months) were available in 128 patients, of whom 57 (45%) had a biopsy performed and 71 had clinical follow-up. Malignancy was diagnosed in 14 of 128 patients (10.9%). There was a statistically significant difference between the median SUV_max of benign thyroid incidentalomas (SUV_max 4.8) vs malignant (SUV_max 6.3), but the wide range of overlap between the two groups yielded no clinically useful SUV_max threshold value to determine malignancy.

CONCLUSION

¹⁸F-FDG positive focal thyroid incidentalomas occurred in 2.2% of oncologic PET/CT scans, and were malignant in 10.9% of 128 patients. This is the lowest reported malignancy rate in a North American study to date, and significantly lower than the average malignancy rate (35%) reported in the literature. Invasive biopsy of all ¹⁸F-FDG positive thyroid incidentalomas, as recommended by some studies, is unwarranted and further research to determine optimal management is needed. There was no clinically useful SUV_max cut-off value to determine malignancy and PET/CT may not be a useful imaging modality to follow these patients conservatively.

Focal fluorine-18 fluorodeoxyglucose-avid parotid findings in patients with lung cancer: prevalence and characteristics

OBJECTIVE

Correct interpretation of incidental tumors is important to plan an appropriate treatment. We assessed the incidence and imaging characteristics of fluorine-18 fluorodeoxyglucose (F-FDG)-avid focal parotid findings (FPFs) in patients with lung cancer.

PATIENTS AND METHODS

FPFs in PET-computed tomography reports of cancer patients were searched. Those with known parotid malignancies, lymphoma, and diffuse F-FDG uptake in the entire parotid gland were not included in the analysis.

RESULTS

FPFs were detected in 38/3120 cancer patients (1.23%), observed as a soft tissue mass with a mean diameter 1.6±0.5 cm (range 0.8-2.7 cm) and a mean maximum standardized uptake value of 7.7±3.7 (range 2.5-17.8). FPFs were observed in 23/604 (3.8%) patients with lung cancer, compared with 6/1366 (0.4%) with breast cancer and 5/842 (0.6%) with gastrointestinal malignancies. We assessed FPFs appearances in 23 patients with lung cancer (18 men, mean age 72.8±9.2); 20 (87%) were current or past smokers. There was no correlation between the stage or histopathological type of the lung cancer and the prevalence of parotid lesions. In four patients with histopathology, no malignancy was detected. For an additional 11 patients with available imaging and clinical follow-up (mean follow-up 15.5±13.5 months, range 3-42 months), FPFs were consistent with benign lesions.

CONCLUSION

FPFs were more prevalent among patients with lung cancer than in patients with other malignancies. As F-FDG avidity was moderate to high, FPFs may mimic distant metastases. It is important to consider FPFs in the interpretation of a focal parotid lesion as misinterpretation may result in denial of appropriate therapy.

Positron Emission Tomography Computed Tomography: A Guide for the General Radiologist

Cancer remains a leading cause of death in Canada and worldwide. Whilst advances in anatomical imaging to detect and monitor malignant disease have continued over the last few decades, limitations remain. Functional imaging, such as positron emission tomography (PET), has improved the sensitivity and specificity in detecting malignant disease. In combination with computed tomography (CT), PET is now commonly used in the oncology setting and is an integral part of many cancer patients' pathways. Although initially the CT component of the study was purely for attenuation of the PET imaging and to provide anatomical coregistration, many centers now combine the PET study with a diagnostic quality contrast enhanced CT to provide one stop staging, thus refining the patient's pathway. The commonest tracer used in everyday practice is FDG (F18-fluorodeoxyglucose). There are many more tracers in routine clinical practice and those with emerging roles, such as 11C-choline, useful in the imaging of prostate cancer; 11C-methionine, useful in imaging brain tumours; C11-acetate, used in imaging hepatocellular carcinomas; 18F-FLT, which can be used as a marker of cellular proliferation in various malignancies; and F18-DOPA and various 68Ga-somatostatin analogues, used in patients with neuroendocrine tumours. In this article we concentrate on FDG PETCT as this is the most commonly available and widely utilised tracer now used to routinely stage a number of cancers. PETCT alters the stage in approximately one-third of patients compared to anatomical imaging alone. Increasingly, PETCT is being used to assess early metabolic response to treatment. Metabolic response can be seen much earlier than a change in the size/volume of the disease which is measured by standard CT imaging. This can aid treatment decisions in both in terms of modifying therapy and in addition to providing important prognostic information. Furthermore, it is helpful in patients with distorted anatomy from surgery or radiotherapy when there is suspicion of recurrent or residual disease. FDG PETCT is not specific for malignancy and can also be used for diagnosing and monitoring a number of inflammatory and infectious conditions that can be difficult to diagnose on anatomical imaging, some of which carry significant morbidity. FDG PETCT is increasingly used in patients with pyrexia of unknown origin and in patients with metastatic malignancies of unidentified primary on conventional imaging. This article reviews the uses of PETCT including an overview of the more common incidental lesions and conditions. It also provides guidance of how to approach a PETCT as a nonradionuclide radiologist and how to interpret a study in the multidisciplinary team setting.

Predictors of pathologic outcome of focal FDG uptake in the parotid gland identified on whole-body FDG PET imaging

PURPOSE

The purpose was to test whether patient's primary malignancy type and presence of F-18-fluorodeoxyglucose (FDG)-avid cervical lymph node(s) are predictors of pathologic outcome of incidental focal FDG-avid parotid lesions.

BASIC PROCEDURES

A retrospective cohort study of pathologically proven incidental cases was performed.

MAIN FINDINGS

Focal parotid FDG uptake in the setting of head and neck cancer/melanoma [odds ratio (OR)=24.6, P<.01], lymphoma (OR=7.2, P=.02), or FDG-avid cervical lymph node(s) (OR=3.6, P=.07) has a higher odds of representing metastases. No malignant primary parotid tumors were incidentally discovered.

PRINCIPAL CONCLUSIONS

In patients with head and neck cancer/melanoma, lymphoma, or FDG-avid cervical lymph node(s), there were higher odds that focal parotid FDG uptake was a metastasis.

Clinical significance of parotid gland incidentalomas on (18)F-FDG PET/CT

The aim of this study was to evaluate the frequency and clinical significance of incidental focal uptake of (18)F-fluorodeoxyglucose (FDG) on positron emission tomography/computed tomography (PET/CT) in the parotid glands of cancer patients. A retrospective review of 7,252 oncologic PET/CT studies was done. FDG positive parotid incidentalomas occurred in 0.4% of PET/CT scans, of which only 4% were malignant. PET/CT was unable to differentiate benign from malignant parotid lesions based on SUVmax alone. (18)F-FDG positive parotid incidentalomas can be managed conservatively, however patients with a prior history of lymphoma had a much higher risk of parotid malignancy and require further investigation.

Prevalence and risk of malignancy of focal incidental uptake detected by fluorine-18-fluorodeoxyglucose positron emission tomography in the parotid gland: a meta-analysis

This study aimed at performing a meta-analysis on the prevalence and risk of malignancy of focal parotid incidental uptake (FPIU) detected by hybrid fluorine-18-fluorodeoxyglucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT) or (18)F-FDG PET alone. A comprehensive literature search of studies published up to July 2014 was performed. Records reporting at least 5 FPIUs were selected. Pooled prevalence and malignancy risk of FPIU were calculated including 95 % confidence intervals (95 % CI). Twelve records were selected for our meta-analysis. Pooled prevalence of FPIU detected by (18)F-FDG PET or PET/CT was 0.6 % (95 % CI 0.4-0.7 %), collecting data of 220 patients with FPIU. Overall, 181 FPIUs underwent further evaluation and 165 FPIUs were pathologically proven. Pooled risk of malignancy was 9.6 % (95 % CI 5.4-14.8 %), 10.9 % (95 % CI 5.8-17.3 %) and 20.4 % (95 % CI 12.3-30 %), considering all FPIUs detected, only those which underwent further evaluation and only those pathologically proven, respectively. Selection bias in the included studies, the heterogeneity among studies and the publication bias are limitations of our meta-analysis. Overall FPIUs are observed in about 1 % of (18)F-FDG PET or PET/CT scans and they are benign in most of the cases. Nevertheless, further evaluation is needed whenever FPIUs are detected by (18)F-FDG-PET or PET/CT to exclude malignant lesions or with possible malignant degeneration. Prospective studies are needed to confirm the findings reported by our meta-analysis.

FDG-PET/CT pitfalls in oncological head and neck imaging

OBJECTIVES

Positron emission tomography-computed tomography (PET/CT) with fluorine-18-fluorodeoxy-D-glucose (FDG) has evolved from a research modality to an invaluable tool in head and neck cancer imaging. However, interpretation of FDG PET/CT studies may be difficult due to the inherently complex anatomical landmarks, certain physiological variants and unusual patterns of high FDG uptake in the head and neck. The purpose of this article is to provide a comprehensive approach to key imaging features and interpretation pitfalls of FDG-PET/CT of the head and neck and how to avoid them.

METHODS

We review the pathophysiological mechanisms leading to potentially false-positive and false-negative assessments, and we discuss the complementary use of high-resolution contrast-enhanced head and neck PET/CT (HR HN PET/CT) and additional cross-sectional imaging techniques, including ultrasound (US) and magnetic resonance imaging (MRI).

RESULTS

The commonly encountered false-positive PET/CT interpretation pitfalls are due to high FDG uptake by physiological causes, benign thyroid nodules, unilateral cranial nerve palsy and increased FDG uptake due to inflammation, recent chemoradiotherapy and surgery. False-negative findings are caused by lesion vicinity to structures with high glucose metabolism, obscuration of FDG uptake by dental hardware, inadequate PET scanner resolution and inherent low FDG-avidity of some tumours.

CONCLUSIONS

The interpreting physician must be aware of these unusual patterns of FDG uptake, as well as limitations of PET/CT as a modality, in order to avoid overdiagnosis of benign conditions as malignancy, as well as missing out on actual pathology.

TEACHING POINTS

• Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies. • Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation. • Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.

Infectious and inflammatory complications of surgical management of cancer patients imaged with 18F-FDG PET/CT: a pictorial essay

The aim of this pictorial essay was to highlight the usefulness of fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in evaluating incidental infection or inflammation in cancer patients, related to surgical management. A retrospective review of 10,985 consecutive oncologic PET/CTs was done, and nine cases with suspected FDG positive infectious or inflammatory processes were selected for further review. PET/CT helped identify infections and inflammatory processes related to surgical management of cancer patients, define the extent of infection or inflammation, guide the management and, in some cases, evaluate response to therapy.

Diagnostic Criteria on (18)F-FDG PET/CT for Differentiating Benign from Malignant Focal Hypermetabolic Lesions of Parotid Gland

PURPOSE

We investigated PET/CT diagnostic criteria for differentiating benign from malignant parotid lesions with focal (18)F-FDG uptake.

METHODS

The subjects of the study were 272 patients who exhibited focal (18)F-FDG uptake of the parotid gland. Sixty-eight pathologically confirmed parotid lesions from 67 patients were included. The maximum SUV (SUVmax), uptake patterns (homogeneous vs. heterogeneous), size measured by CT, maximum Hounsfield units (HUmax) and margins on CT (well vs. ill defined) of each parotid lesion on PET/CT images were compared with final diagnoses.

RESULTS

Thirty-two parotid lesions were histologically proven to be malignant. There were significant differences in uptake patterns (cancer incidence, heterogeneous:homogeneous = 79.2%:29.5%, p < 0.0001) and margins on CT (cancer incidence, ill:well defined = 84.4%:13.3%, p < 0.0001) between benign and malignant lesions. The cancer risks of parotid lesions were 89.5% with heterogeneous uptake and ill-defined margins, 70.6% with heterogeneous uptake or ill-defined margins (no overlap in subjects) and 9.3% with homogeneous uptake and well-defined margins (p < 0.0001). When any lesion with heterogeneous uptake or ill-defined margins was regarded as malignant, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 90.6% (29/32), 80.6% (29/36), 80.6% (29/36), 90.6% (29/32) and 85.6% (58/68), respectively. For predicting malignancy, combined PET/CT criteria showed better sensitivity, NPV and accuracy than PET-only criteria, and had a tendency to have more accurate results than CT-only criteria. There were no significant differences in SUVmax, size or HUmax between benign and malignant lesions.

CONCLUSION

Uptake patterns and margins on CT are useful PET/CT diagnostic criteria for differentiating benign from malignant lesions.

Atlas of confounding factors in head and neck PET/CT imaging

PURPOSE

Interpretation of positron emission tomography/computed tomography (PET/CT) studies in the head and neck region is challenging due to the complex anatomy and nonspecific physiologic and inflammatory FDG uptake. We present an atlas of common confounding factors encountered at our institution.

MATERIALS AND METHODS

We present whole-body fluorodeoxyglucose (FDG) PET/CT studies of 20 patients with various confounding factors in the head and neck. Most patients (15) had a history of head and neck cancer and some (5) of them presented with other primary tumors.

RESULTS

We describe these cases under the following categories: physiologic uptake (6), inflammatory uptake (5), unexpected benign tumors (2), unexpected malignant tumors (4), postradiation changes (2), postsurgical changes (2), and misregistration (1).

CONCLUSIONS

Knowledge of common variants, pitfalls, and treatment effects is essential in accurate reading of PET/CT in the head and neck region.

Physiology and pathophysiology of incidental findings detected on FDG-PET scintigraphy

A routine feature of positron emission tomography/computed tomography (PET/CT) imaging is whole-body acquisition that results in many unexpected findings identified outside of the primary region of abnormality. Furthermore, (18)F-fluorodeoxyglucose (FDG) is a marker of glycolysis and does not specifically accumulate in malignancy. Understanding the physiology and pathophysiology of normal FDG distribution and common incidental findings is therefore essential to the physician interpreting whole-body FDG-PET/CT studies. Whereas many incidental findings are benign and of limited clinical significance, others represent uncommon manifestations of the primary malignancy, second malignancies, or various clinically significant pathologic processes. Patients with a single malignancy are at greater risk of developing synchronous or metachronous second malignancies, possibly related to exposure to shared carcinogenic agents or presence of prooncogenic mutations. The decision of how to pursue an intervention on the basis of an incidental finding is generally left to clinical judgment.

Efficacy of conventional whole-body ¹⁸F-FDG PET/CT in the incidental findings of parotid masses

OBJECTIVE

The objective of this study was to evaluate the incidence of incidental parotid masses with conventional whole-body ¹⁸F-deoxyglucose (FDG) PET/CT and assess the ability of PET/CT to characterize these unexpected parotid lesions.

METHODS

Fifty eight incidental findings of parotid masses with routine FDG PET/CT whole-body scan were reviewed in this retrospective analysis, which were selected from the patients without any known or suspected parotid disease in our PET center, from June 2005 to May 2009. 51 cases were operated or underwent a biopsy after a short-term PET/CT study; the remaining 7 cases had a follow-up. Parotid mass that showed both noncontrast CT (irregular shape and blurry border) and PET malignant features (high FDG uptake, SUV(max) > 3.0) was considered as positive for malignancy. Correlation of FDG PET/CT with histology or follow-up outcome was performed.

RESULTS

Fifty eight unexpected findings of parotid masses accounted for 0.3% of the total cases in 4 years, including 11 (19.0%) malignant tumors and 47 (81.0%) benign lesions. 13 lesions manifested single nodule with malignant CT features and intense FDG activity, of which 6 were proved to be malignant; thus, sensitivity and positive predictive values were 54.5% (6 of 11) and 46.2% (6 of 13), respectively. 45 lesions showed either single nodule with benign CT features, or a low FDG uptake (SUV(max) ≤ 3.0), of which 40 were true negatives; therefore, specificity and negative predictive values were 85.1% (40 of 47) and 88.9% (40 of 45), respectively. All parotid masses except 9 benign and 1 malignant showed a high FDG uptake. Compared with SUV only, combined interpretation of PET and CT results displayed a lower sensitivity (90.9-54.5%), but a higher specificity (19.1-85.1%) and a higher overall accuracy.

CONCLUSIONS

Whole-body FDG-PET/CT at the time of surveying the entire body condition is helpful for detecting the asymptomatic parotid masses. Combined noncontrast CT is an essential evidence for improving the diagnostic accuracy of FDG-PET/CT for parotid masses.

Incidental breast lesions identified by 18F-fluorodeoxyglucose-positron emission tomography

BACKGROUND

Positron emission tomography (PET) scanning is now part of the standard evaluation for patients with a variety of different malignancies. We describe our experience with breast incidentalomas in a large series of PET scans performed for patients without a known history of breast cancer.

MATERIALS AND METHODS

From March 2000 through June 2007, approximately 45,000 PET scans were performed; 163 had breast findings unrelated to the primary malignancy. In 103 of 163 (63%), findings included physiologic variation, lactation, implants, or benign calcifications. Chart review was conducted in the remaining 60 of 163 patients (37%).

RESULTS

In 20 of 60 patients (33%), no additional evaluation was performed due to advanced stage of the primary malignancy; 40 of 60 (67%) underwent additional imaging and evaluation. In 16 of 40 patients (40%), the lesion resolved on repeat PET; the lesion persisted in 10 of 40 (25%). Additional breast imaging was performed in 14 of 40 (35%). In total, 12 of 40 (30%) underwent biopsy; 7 of 40 (18%) were positive for malignancy.

CONCLUSIONS

In our experience, 29% of breast incidentalomas (7 of 24) with persistent imaging findings were malignant. Further evaluation of these lesions should be based on overall clinical status. In patients where results would not change overall management, biopsy may not be warranted.

Incidental PET/CT findings in the cancer patient: how should they be managed?

BACKGROUND

Despite a paucity of evidence-based guidelines, the use of PET/CT (positron emission tomography/computed tomography) in the management of cancer patients is increasing. As widespread clinical application increases, unexpected radiographic findings are occasionally identified. These incidental findings are often suspicious for a second primary malignancy. The purpose of this study was to determine the clinical impact of these incidental PET/CT findings.

METHODS

A query of our prospectively acquired Nuclear Medicine database was performed to identify patients with a known malignancy being staged or serially imaged with PET/CT. Patients with incidental findings suggestive of a second primary malignancy were selected. Statistical analysis was performed to determine the ability of PET/CT to identify a second primary malignancy. All PET/CT were interpreted by board certified nuclear radiologists.

RESULTS

Of 3,814 PET/CT scans performed on 2,219 cancer patients at our institution from January 1, 2005, to December 29, 2008, 272 patients (12% of all patients) had findings concerning for a second primary malignancy. An invasive work-up was performed on 49% (133/272) of these patients, while 15% (40/272) had no further evaluation due to an advanced primary malignancy. The remaining 36% (99/272) had no further evaluation secondary to a low clinical suspicion determined by the treating team, a clinical plan of observation, or patients lost to follow-up. Of the 133 patients evaluated further, clinicians identified a second primary malignancy in 41 patients (31%), benign disease in 62 patients (47%), and metastatic disease from their known malignancy in 30 patients (23%). The most common sites for a proven second primary malignancy were: lung (N = 10), breast (N = 7), and colon (N = 5). Investigation of these lesions was performed using several techniques, including 24 endoscopies (6 malignant). A surgical procedure was performed in 74 patients (29 malignant), and a percutaneous biopsy was performed on 34 patients (12 malignant). The overall positive predictive value for PET/CT to detect a second primary malignancy was 31% in this subgroup. At a median follow-up of 22 months, 9 of 41 patients with a second primary were dead of a malignancy, 20 were alive with disease, and 12 had no evidence of disease.

CONCLUSION

Incidental PET/CT findings consistent with a second primary are occasionally encountered in cancer patients. In our data, approximately half of these findings were benign, a third were consistent with a second primary malignancy or a metastatic focus, and the remainder were never evaluated due to physician and patient decision. Advanced primary tumors are unlikely to be impacted by a second primary tumor suggesting that this subset of patients will not benefit from further investigation. Our data suggests that, despite the high rate of false positivity, incidental PET/CT findings should be investigated when the results will impact treatment algorithms. The timing and route of investigation should be dictated by clinical judgment and the status of the primary tumor. Further investigation will need to be performed to determine the long-term clinical impact of incidentally identified second primary malignancies.

Parotid incidentaloma identified by combined 18F-fluorodeoxyglucose whole-body positron emission tomography and computed tomography: findings at grayscale and power Doppler ultrasonography and ultrasound-guided fine-needle aspiration biopsy or core-needle biopsy

Twelve parotid incidentalomas in 10 consecutive subjects (nine with a known malignancy elsewhere and one presumptively healthy subject) identified by combined 18F-fluorodeoxyglucose whole-body positron emission tomography and computed tomography (18F-FDG PET/CT) were investigated, with the aim of calculating maximum standardized uptake value (SUV(max)) of each FDG-avid focus, and identifying corresponding sonographic and pathologic findings. The results of ultrasound-guided fine-needle aspiration biopsy (FNAB) (n = 9) and core-needle biopsy (CNB) (n = 3) were Warthin tumor in 10 cases, and pleomorphic adenoma and chronic inflammation in one each. SUV(max) was 7.0-21.0 g/mL (average 13.7 g/mL) for Warthin tumor, 6.8 g/mL for pleomorphic adenoma, and 7.3 g/mL for chronic inflammation. Each FDG-avid focus corresponded to ovoid (n = 11) or lobulated (n = 1) hypoechoic mass on grayscale ultrasonography (US) and hypervascular mass, except one with chronic inflammation, on power Doppler (PD) US. Parotid incidentaloma identified by 18F-FDG PET/CT during workup of various malignancies elsewhere does not necessarily signify primary or metastatic malignancy, but indicates a high likelihood of benign lesions, particularly Warthin tumor. Such lesions should be evaluated thoroughly by US and ultrasound-guided FNAB or CNB if parotid disease would change the patient's treatment plan.

Incidental head and neck (18)F-FDG uptake on PET/CT without corresponding morphological lesion: early predictor of cancer development?

PURPOSE

To retrospectively determine whether increased/asymmetric FDG uptake on PET without a correlating morphological lesion on fully diagnostic CT indicates the development of a head and neck malignancy.

METHODS

In 590 patients (mean age 55.4 +/- 13.3 years) without a head and neck malignancy/inflammation FDG uptake was measured at (a) Waldeyer's ring, (b) the oral floor, (c) the larynx, and (d) the thyroid gland, and rated as absent (group A), present (group B), symmetric (group B1) or asymmetric (group B2). Differences between groups A and B and between B1 and B2 were tested for significance with the U-test (p < 0.05). An average follow-up of about 2.5 years (mean 29.5 +/- 13.9 months) served as the reference period to determine whether patients developed a head and neck malignancy.

RESULTS

Of the 590 patients, 235 (40%) showed no evidence of enhanced FDG uptake in any investigated site, and 355 (60%) showed qualitatively elevated FDG uptake in at least one site. FDG uptake values (SUV(max), mean+/-SD) for Waldeyer's ring were 3.0 +/- 0.89 in group A (n = 326), 4.5 +/- 2.18 in group B (n = 264; p < 0.01), 5.4 +/- 3.35 in group B1 (n = 177), and 4.1 +/- 1.7 in group B2 (n = 87; p < 0.01). Values for the oral floor were 2.8 +/- 0.74 in group A (n = 362), 4.7 +/- 2.55 in group B (n = 228; p < 0.01), 4.4 +/- 3.39 in group B1 (n = 130), and 5.1 +/- 2.69 in group B2 (n = 98, p = 0.01). Values for the larynx were 2.8 +/- 0.76 in group A (n = 353), 4.2 +/- 2.05 in group B (n = 237; p < 0.01), 4.0 +/- 2.02 in group B1 (n = 165), and 4.6 +/- 2.8 in group B2 (n = 72; p = 0.027). Values for the thyroid were 2.4 +/- 0.63 in group A (n = 404), 3.0 +/- 1.01 in group B (n = 186; p < 0.01), 2.6 +/- 0.39 in group B1 (n = 130), and 4.0 +/- 1.24 in group B2 (n = 56; p < 0.01). One patient developed a palatine tonsil carcinoma (group B1, SUV(max) 3.2), and one patient developed an oral floor carcinoma (group B1, SUV(max) 3.7).

CONCLUSION

Elevated/asymmetric head and neck FDG accumulation without a correlating morphological lesion can frequently be found and does not predict cancer development. In populations in which goitre is endemic, FDG uptake by the thyroid is common and not associated with thyroid cancer.