title: Characteristics of primary papillary thyroid carcinoma with false-negative findings on initial (18)F-FDG PET/CT.
abstract: BACKGROUND
  We often observe that uptake of tracer is not detected in the primary cancer focus in patients with histologically proven papillary thyroid carcinoma (PTC) on preoperative (18)F-fluorodeoxyglucose positron emission tomography-computed tomography ((18)F-FDG PET/CT). Therefore, we analyzed the clinical and pathologic variables affecting false-negative findings in primary tumors on preoperative (18)F-FDG PET/CT.
  
  
  METHODS
  We retrospectively reviewed the medical records of 115 consecutive patients who underwent (18)F-FDG PET/CT for initial evaluation and were diagnosed with PTC by postoperative permanent biopsy. The clinical and pathologic characteristics that influence the (18)F-FDG PET/CT findings in these patients were analyzed with respect to the following variables: age, gender, tumor size, multifocality of the primary tumor, perithyroidal invasion, lymphovascular or capsular invasion, and central lymph node metastasis-based final pathology.
  
  
  RESULTS
  Twenty-six (22.6%) patients had false-negative (18)F-FDG PET/CT findings. In patients with negative (18)F-FDG PET/CT findings, tumor size, and perithyroidal and lymphovascular invasion were significantly less than in patients with positive (18)F-FDG PET/CT findings. Tumors >1 cm in size were correlated with (18)F-FDG PET/CT positivity. On multivariate analysis, perithyroidal invasion (P = 0.026, odds ratio = 7.714) and lymphovascular invasion (P = 0.036, odds ratio = 3.500) were independent factors for (18)F-FDG PET/CT positivity. However, there were no significant differences between (18)F-FDG PET/CT positivity and age, gender, capsular invasion, and central lymph node metastasis based on final pathology.
  
  
  CONCLUSIONS
  Tumor size and perithyroidal and lymphovascular invasion of papillary carcinoma can influence (18)F-FDG PET/CT findings. Absence of perithyroidal and lymphovascular invasion were independent variables for false-negative findings on initial (18)F-FDG PET/CT in patients with PTC.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Chungnam National University College of Medicine, School of Medicine, Daejeon, Korea.
authors.forename: Jin Woong
authors.initials: JW
authors.lastname: Choi
authors.forename: Young Hoon
authors.initials: YH
authors.lastname: Yoon
authors.forename: Yeo Hoon
authors.initials: YH
authors.lastname: Yoon
authors.forename: Seong Min
authors.initials: SM
authors.lastname: Kim
authors.forename: Bon Seok
authors.initials: BS
authors.lastname: Koo
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002291:Carcinoma, Papillary / Q000175:diagnosis* / Q000601:surgery; D005188:False Negative Reactions; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D049268:Positron-Emission Tomography; D011379:Prognosis; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000601:surgery; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18