Abstract
PurposeTo quantify incidental thyroid pathology including malignancy on routine 18F-FDG PET-CT scansTo compare standardised uptake values (SUVmax) in thyroid malignancy subtypesMethods and materialsThis is a retrospective study of all 18F-FDG PET-CT scans (n = 6179) performed in a teaching hospital between June 2010 and May 2019. RIS database search of reports for the word “thyroid” was performed. Studies with evidence of thyroid uptake were included. Patient age and gender, primary indication for PET scan (malignant or non-malignant), thyroid result on PET (diffuse or focal tracer uptake, SUVmax), ultrasound and FNAC results were recorded.ResultsIncidental abnormal thyroid tracer uptake as a proportion of all 18F-FDG PET-CT scans was 4.37% (n = 270). Out of region patients (n = 87) whose records could not be obtained were excluded leaving a study group of n = 183. Ninety-four in this group had focal uptake, and 89 had diffuse uptake. Fifty-five patients in the focal group had undergone further investigations. Of these, 30 were thought to be benign on USS alone, and 25 patients underwent USS/FNAC. Thirteen (24%) malignancies were identified (5 papillary, 6 follicular, 1 poorly differentiated thyroid cancer, 1 metastatic malignancy). Mean SUVmax for papillary carcinoma was noted to be 8.2 g/ml, and follicular carcinoma was 12.6 g/ml.ConclusionIncidental abnormal thyroid 18F-FDG PET-CT uptake in PET-CT scans of 4.37% is in keeping with the known limited literature. Rather similar number of patients was noted in the focal and diffuse tracer uptake categories in the final study group. Around quarter of the focal lesions were identified to be malignant, implying focal lesions should always be further investigated.
Highlights
The increasing role of PET-CT in oncological and non-oncological conditions has resulted in an increased detection of PET-CT incidentalomas, commonly involving the thyroid gland (The Royal College of radiologists, 2012; Delivanis & Castro, 2018; Vassiliadi & Tsagarakis, 2011).The tracer 18F-FDG1 used in PET-CT can incidentally accumulate in the thyroid gland, either diffusely or focally
Incidental focal 18F-FDG uptake within the thyroid gland has previously been found to occur in 1.2–4.3% of all PET-CT scans in patients scanned for an alternative indication (Kao et al, 2012; Soelberg et al, 2012; Cohen et al, 2001; Kang et al, 2003; Chen et al, 2005; Chen et al, 2009; Ho et al, 2011)
The primary aim of our study was to quantify incidental thyroid malignancy on 18FFDG PET-CT in patients scanned for an alternative indication
Summary
The increasing role of PET-CT in oncological and non-oncological conditions has resulted in an increased detection of PET-CT incidentalomas, commonly involving the thyroid gland (The Royal College of radiologists, 2012; Delivanis & Castro, 2018; Vassiliadi & Tsagarakis, 2011).The tracer 18F-FDG1 used in PET-CT can incidentally accumulate in the thyroid gland, either diffusely or focally. Incidental focal 18F-FDG uptake within the thyroid gland has previously been found to occur in 1.2–4.3% of all PET-CT scans in patients scanned for an alternative indication (Kao et al, 2012; Soelberg et al, 2012; Cohen et al, 2001; Kang et al, 2003; Chen et al, 2005; Chen et al, 2009; Ho et al, 2011). Patients with focal uptake within the thyroid gland are at a higher risk of malignancy, with studies reporting between 26 and 50% (Kao et al, 2012; Soelberg et al, 2012; Cohen et al, 2001; Chen et al, 2005; Chen et al, 2009; Kim et al, 2005; Chu et al, 2006; Bae et al, 2009). Further investigation of focal 18F-FDG uptake with ultrasound and FNAC2 is recommended because of this increased risk of malignancy (Pencharz et al, 2018; Haugen et al, 2015; Hoang et al, 2015)
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