title: Radiological features of metastases to the thyroid.
abstract: BACKGROUND
  Thyroid metastases (TM) are uncommon. Dependent on study design, the reported frequency of TM is in the range of 0.1-6% in different analyses. While clinical and histopathological features of TM were well described in the literature, radiological publications consist predominantly of isolated case reports or small series.
  
  
  OBJECTIVE
  To estimate the prevalence, clinical signs, and radiological appearances of TM.
  
  
  METHODS
  From 1997 to 2013, a total of 8849 patients with various disorders of the thyroid gland were treated in our institution. In 33 patients TM were diagnosed. Ultrasound (US) images were available in all patients, computed tomography (CT) of the neck in 16 patients, and magnetic resonance imaging (MRI) in nine patients.
  
  
  RESULTS
  Clinically, most patients (85%) presented with a painless neck mass. Primary tumors were renal cell carcinoma (79%), colorectal cancer (12%), lung cancer (3%), rhabdomyosarcoma (3%), and breast carcinoma (3%). On US, most lesions were irregular in shape with inhomogenous texture. On CT, all TM were hypodense. On T1-weighted images, most TM were inhomogenously iso-to-hyperintense in comparison to the normal thyroid tissue, and slightly hyperintense on T2-weighted images with an inhomogenous contrast enhancement.
  
  
  CONCLUSIONS
  The prevalence of TM was 0.4%. Most of the TM originated from renal cell carcinoma. The identified radiological features of TM should be taken into consideration in the differential diagnosis of thyroid lesions.
authors.affiliation: Department of Radiology, Martin Luther University Halle-Wittenberg, Halle, Germany alex.surow@medizin.uni-halle.de.
authors.forename: Alexey
authors.initials: A
authors.lastname: Surov
authors.affiliation: Department of Surgery, Martin Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Machens
authors.affiliation: Department of Pathology, Martin Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Holzhausen
authors.affiliation: Department of Radiology, Martin Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Rolf Peter
authors.initials: RP
authors.lastname: Spielmann
authors.affiliation: Department of Surgery, Martin Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Dralle
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013961:Thyroid Gland / Q000000981:diagnostic imaging / Q000473:pathology; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000556:secondary*; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography; D055815:Young Adult
keywords: Thyroid metastases; computed tomography (CT); imaging findings; magnetic resonance imaging (MRI); prevalence; ultrasound