title: Thyroid nodules with minimal cystic changes have a low risk of malignancy.
abstract: OBJECTIVE
  The goal of this study was to determine the risk of malignancy of thyroid nodules with minimal cystic changes.
  
  
  METHODS
  A total of consecutive 1,000 thyroid nodules (≥1 cm) with final diagnoses from twoinstitutions were included in this study. The risk of malignancy of thyroid nodules was analyzed according to the internal content, which was categorized as purely solid, minimally cystic (cystic changes ≤10%), and partially cystic (cystic changes >10%). We also assessed the risk of malignancy of nodules with minimal cystic changes depending on echogenicity and presence of any suspicious ultrasonografic (US) features.
  
  
  RESULTS
  The overall frequency of purely solid, minimally cystic, and partially cystic noduleswas 730/1,000 (73%), 61/1,000 (6.1%), and 209/1,000 (20.9%), respectively, with risks ofmalignancy of 14.8% (108/730), 3.3% (2/61), and 3.3% (7/209), respectively. The risk ofmalignancy of nodules with minimal cystic changes was significantly lower than that of purelysolid nodules (P=0.013). The risk of malignancy of nodules with minimal cystic changes was also lower than that of purely solid nodules in the group of hypoechoic nodules (P=0.063) and in the group of nodules with suspicious US features (P=0.028), but was not significantly different from that of partially cystic nodules regardless of echogenicity or the presence of suspicious US features (P≥0.652).
  
  
  CONCLUSIONS
  Thyroid nodules with minimal cystic changes have a low risk of malignancy, similar to that of partially cystic nodules regardless of echogenicity or the presence of suspicious US features. The US lexicon could define solid nodules as nodules with purely solid internal content in order to enhance the accuracy of estimated risks of malignancy.
authors.affiliation: Department of Radiology, Human Medical Imaging and Intervention Center, Seoul, Korea.
authors.forename: Dong Gyu
authors.identifier: 0000-0001-6422-1652
authors.initials: DG
authors.lastname: Na
authors.affiliation: Department of Radiology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Ji-Hoon
authors.identifier: 0000-0002-6349-6950
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Radiology, Human Medical Imaging and Intervention Center, Seoul, Korea.|Department of Radiology, Incheon Medical Center, Incheon, Korea.
authors.forename: Dea Sik
authors.identifier: 0000-0001-8424-8561
authors.initials: DS
authors.lastname: Kim
authors.affiliation: Department of Radiology, Human Medical Imaging and Intervention Center, Seoul, Korea.|Department of Radiology, New Korea Hospital, Gimpo, Korea.
authors.forename: Soo Jin
authors.identifier: 0000-0001-8233-1388
authors.initials: SJ
authors.lastname: Kim
keywords: Diagnosis; Neoplasm; Thyroid nodule; Ultrasonography