title: A six-year-old boy with a suspicious thyroid nodule: intrathyroidal thymic tissue.
abstract: BACKGROUND
  Ectopic intrathyroidal thymus tissue that forms mass lesions as a consequence of aberrant thymic migration during embryogenesis is rarely reported in the literature.
  
  
  METHODS
  We present the case of a 6-year-old boy with a right thyroid nodule and bilateral cervical lymph nodes. Thyroid hormone, antibodies, and routine chemistry tests were normal. Real-time thyroid ultrasound showed a right calcified nodule measuring 8 x 5 x 7 mm and multiple bilateral cervical lymph nodes. I131 scan showed mild decreased uptake in the right upper lobe. On fine-needle aspiration biopsy we discovered an atypical lymphoid proliferation that was suspicious, although not diagnostic, of a lymphoma. Immunostain for calcitonin was negative. Flow cytometry of the thyroid nodule aspirate demonstrated an abnormal polyclonal T cell population with dual expression of CD4 and CD8, and a subpopulation of cells that expressed TdT suggesting the possibility of lymphoblastic lymphoma. DNA analysis, as well as polymerase chain reaction for T cell and B cell gene rearrangement, did not demonstrate changes in the gene for the heavy chain of immunoglobulin of B cells and gamma chain of the T cell receptor. Lymph node aspirate showed unremarkable T and B lymphoid cells.
  
  
  RESULTS
  The diagnosis of ectopic intrathyroidal thymus was made after the operation.
  
  
  CONCLUSIONS
  Ectopic thymus tissue should be considered in the differential diagnosis of thyroid masses, especially in children.
authors.affiliation: Department of Medicine, Division of Endocrinology, Diabetes and Metabolism University of Miami Miller School of Medicine, Miami, Florida, USA. chernandez@med.miami.edu
authors.forename: Carlos
authors.initials: C
authors.lastname: Hernandez-Cassis
authors.forename: Anna
authors.initials: A
authors.lastname: Poniecka
authors.forename: Claudia K
authors.initials: CK
authors.lastname: Vogel
authors.forename: J Maxwell
authors.initials: JM
authors.lastname: McKenzie
mesh_terms: D002114:Calcinosis / Q000175:diagnosis; D002648:Child; D002828:Choristoma / Q000175:diagnosis*; D003937:Diagnosis, Differential; D006801:Humans; D008297:Male; D013950:Thymus Gland; D013959:Thyroid Diseases / Q000175:diagnosis*; D016606:Thyroid Nodule / Q000175:diagnosis*