title: Thyroid Carcinoma Detected by 18F-Fluorodeoxyglucose Positron Emission Tomography Among Individuals Without Prior Evidence of Thyroid Disease: Relevance and Clinicopathologic Features.
abstract: OBJECTIVE
  The expanding use of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) has contributed to an increasing number of thyroid incidentalomas. The present study aimed to estimate the prevalence of 18F-FDG-PET thyroid incidentalomas and evaluate the clinicopathologic features of thyroid malignancies detected by 18F-FDG-PET.
  
  
  METHODS
  We reviewed all 18F-FDG-PET exams performed at the Portuguese Institute of Oncology, Lisbon, between 2007 and 2012 (n = 9,374). The inclusion criteria were focal thyroid uptake and absence of known thyroid disease.
  
  
  RESULTS
  Focal thyroid uptake was observed in 60 out of 9,374 18F-FDG-PET exams (prevalence of 0.64%). Fine-needle aspiration cytology (FNAC) was performed in 23 patients and reported as malignant in 14 cases (56.5% primary thyroid carcinoma; 4.3% secondary malignancy), as benign in 7 cases (30.5%) and as follicular lesion of undetermined significance in 2 cases (8.7%). Fourteen patients had surgery. A final histologic diagnosis of papillary thyroid carcinoma was established in 12 cases (52.2%). Three were multifocal (25.0%); 8 had extrathyroidal extension (66.7%); 5 had angioinvasion (41.7%); 3 had lymph nodes metastases (25.0%) and 2 showed lung metastases (16.7%). Overall, 91.7% were classified as intermediate or high risk. All patients had radioiodine therapy. At the last observation (mean follow-up was 29.9 months), persistent or recurrent disease was identified in 4 patients (33.3%) and none died from thyroid malignancy.
  
  
  CONCLUSIONS
  Thyroid carcinomas disclosed by 18F-FDG-PET are associated with aggressive histological criteria likely to carry a worse prognosis.
authors.affiliation: Department of Endocrinology, Instituto Portuguěs de Oncologia de Lisboa.
authors.forename: Pedro
authors.initials: P
authors.lastname: Marques
authors.affiliation: Department of Nuclear Medicine Department, Instituto Portuguěs de Oncologia de Lisboa.
authors.forename: Pedro
authors.initials: P
authors.lastname: Ratão
authors.affiliation: Department of Nuclear Medicine Department, Instituto Portuguěs de Oncologia de Lisboa.
authors.forename: Lucília
authors.initials: L
authors.lastname: Salgado
authors.affiliation: Department of Endocrinology, Instituto Portuguěs de Oncologia de Lisboa University Clinic of Endocrinology, Faculdade de Ciěncias Médicas, Universidade Nova de Lisboa.
authors.forename: Maria João
authors.initials: MJ
authors.lastname: Bugalho