title: Intrathyroidal ectopic thymic tissue mimicking thyroid cancer in children.
abstract: OBJECTIVE
  To increase awareness of the important differential diagnosis between thyroid cancer and intrathyroidal ectopic thymic tissue when performing neck ultrasound (US) in pediatric patients.
  
  
  METHODS
  We report 2 cases of intrathyrodal thymic tissue that were initially referred as possible papillary thyroid cancer (PTC). US and cytologic features of these lesions are described, and the distinguishing US characteristics of intrathyroidal thymic tissue versus PTC are discussed.
  
  
  RESULTS
  Two pediatric patients who underwent thyroid US were diagnosed with thyroid nodules suggestive of PTC. The suspected lesions in both patients exhibited an echo texture identical to the normal thymus gland. Fine-needle aspirate (FNA) biopsy of the nodule in the first case revealed numerous lymphocytes with positive immunocytochemical staining for CD3, confirming a T cell phenotype. The second patient underwent follow-up US imaging 8 months later that showed stability of the intrathyroidal nodule.
  
  
  CONCLUSIONS
  Intrathyroidal ectopic thymic tissue can be mistaken for PTC as both conditions have similar US features. Increased awareness of this unique mimicry may help to avoid unnecessary invasive investigations and surgery in these young patients.
authors.affiliation: Department of Endocrinology, Royal Free Hospital, London, United Kingdom.
authors.forename: Chiaw Ling
authors.initials: CL
authors.lastname: Chng
authors.affiliation: Department of Cellular Pathology, University College Hospital, London, United Kingdom.
authors.forename: Gabriejela
authors.initials: G
authors.lastname: Kocjan
authors.affiliation: Centre for Endocrine Surgery University College Hospital, Great Ormond Street Hospital, London, United Kingdom.
authors.forename: Tom R
authors.initials: TR
authors.lastname: Kurzawinski
authors.affiliation: Department of Radiology, University College Hospital, London, United Kingdom.
authors.forename: Tim
authors.initials: T
authors.lastname: Beale