title: Collapsing benign cystic nodules of the thyroid gland: sonographic differentiation from papillary thyroid carcinoma.
abstract: OBJECTIVE
  The US features of benign and malignant nodules overlap, and benign thyroid lesions can mimic thyroid malignancy on US. Benign cystic nodules after spontaneous collapse or needle aspiration, can mimic malignant thyroid nodules. Our aim was to evaluate the US features of CBCNs of the thyroid that distinguish such nodules from malignant thyroid nodules.
  
  
  METHODS
  US and clinical findings in 13 patients, each with a single CBCN, were evaluated to determine if they showed >50% cystic content on initial US or CT and >30% decrease in maximum diameter on follow-up US. We compared these findings with those of 26 patients, each with a single surgically confirmed PTMC. US scans were analyzed for internal content, shape, margin, echogenicity, presence of echogenic dots suggesting micro- and macrocalcification, inner isoechoic rim, and low-echoic halo.
  
  
  RESULTS
  Six of the 13 (46%) CBCNs were classified as malignant on US due to their marked hypoechogenicity, microcalcification, or spiculated margins. US features that differed between CBCNs and PTMCs were shape (ovoid-to-round versus taller-than-wide, P = .016); margins (ill-defined versus spiculated, P < .000); low-echoic halo (P < .000); inner isoechoic rim (P < .000) with high negative predictive values (100%, 91%, 91%, and 89%, respectively); and clinically acceptable diagnostic accuracy (59%, 80%, 82%, and 85%, respectively).
  
  
  CONCLUSIONS
  US features helpful for differential diagnosis of CBCNs from PTMCs include shape, margin, and the presence of an inner isoechoic rim and a low-echoic halo. Familiarity with US features suggesting CBCNs may be helpful in reducing unnecessary repeated FNABs.
authors.affiliation: Department of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.
authors.forename: M-S
authors.initials: MS
authors.lastname: Ko
authors.forename: K S
authors.initials: KS
authors.lastname: Jeong
authors.forename: Y K
authors.initials: YK
authors.lastname: Shong
authors.forename: G Y
authors.initials: GY
authors.lastname: Gong
authors.forename: J H
authors.initials: JH
authors.lastname: Baek
authors.forename: J H
authors.initials: JH
authors.lastname: Lee
mesh_terms: D000328:Adult; D002291:Carcinoma, Papillary / Q000000981:diagnostic imaging*; D003560:Cysts / Q000000981:diagnostic imaging*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013961:Thyroid Gland / Q000000981:diagnostic imaging*; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging*; D014463:Ultrasonography / Q000379:methods*