title: Ultrasound classification of solitary renal cysts in children.
abstract: BACKGROUND
  Solitary renal cysts are typically incidentally found in children who have undergone renal ultrasound (US). The main concern is a cystic tumor. There is no US-based grading system for children to guide management.
  
  
  OBJECTIVE
  To evaluate a US-based, modified Bosniak grading system in order to differentiate between simple (grade I or II) and complex (grade II or IV) renal cysts and guide management in children.
  
  
  METHODS
  This was a retrospective (2003-2011) study of 212 children (114 females), age range one day to 17 years (mean 8.4 years), with solitary renal cysts diagnosed by US. Two radiologists, who were independent and blinded to clinical information, graded the cysts using the modified Bosniak classification system. In children with more than one year of follow-up US, the change (>10%) in cyst diameter was evaluated. Inter-observer variability (Kappa) was calculated.
  
  
  RESULTS
  Radiologists one and two saw simple renal cysts in 96.2-96.6% (204-205/212) of the children. Ten children had complex renal cysts, as rated by either of the radiologists. There was good inter-observer agreement (kappa = 0.65) for simple versus complex cysts. In 20.2% (18/89) of the children, the cysts increased in size. A definitive diagnosis was obtained in 8.5% (18/212) of the children. A cystic tumor (multilocular cystic nephroma) was found in one child (Figure) with a complex cyst (graded III by both radiologists).
  
  
  CONCLUSIONS
  The use of a modified Bosniak classification system to grade renal cysts was found to have good inter-observer variability (kappa = 0.65) in differentiating between simple and complex renal cysts. Using this classification, few (<4%) renal cysts were classified as complex. Cystic tumors are rare and the only cystic tumor (multilocular cystic nephroma) was classified as complex renal cysts by the two radiologists. Growth of simple, solitary renal cyst is common (20.2%) and, therefore, if not associated with other imaging findings, is not an indication for a cystic tumor. There were limitations inherent in the retrospective nature of the study and because only one child had a cystic tumor.
  
  
  CONCLUSIONS
  The modified Bosniak classification system demonstrated good inter-observer agreement, and identified the single tumor as a complex cyst. The vast majority of solitary renal cysts in children are simple and if asymptomatic, they require no other imaging evaluation. Complex renal cysts are uncommon and should be evaluated with a pre-intravenous and postintravenous contrast CT scan to exclude a tumor.
authors.affiliation: Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Riley Hospital for Children, 705 Riley Hospital Drive, Room 1053, Indianapolis, IN 46202, USA. Electronic address: bkarmazy@iupui.edu.
authors.forename: B
authors.initials: B
authors.lastname: Karmazyn
authors.affiliation: Department of Radiology, Memorial Hospital of South Bend, 615 N. Michigan Street, South Bend, IN 46601, USA. Electronic address: tawadros.alex@gmail.com.
authors.forename: A
authors.initials: A
authors.lastname: Tawadros
authors.affiliation: Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Riley Hospital for Children, 705 Riley Hospital Drive, Room 1053, Indianapolis, IN 46202, USA. Electronic address: ldelaney@iupui.edu.
authors.forename: L R
authors.initials: LR
authors.lastname: Delaney
authors.affiliation: Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Riley Hospital for Children, 705 Riley Hospital Drive, Room 1053, Indianapolis, IN 46202, USA. Electronic address: mbshelto@iupui.edu.
authors.forename: M B
authors.initials: MB
authors.lastname: Marine
authors.affiliation: Department of Urology, Indiana University School of Medicine, Riley Hospital for Children, 705 Riley Hospital Drive, Room 4230, Indianapolis, IN 46202, USA. Electronic address: mpcain@iupui.edu.
authors.forename: M P
authors.initials: MP
authors.lastname: Cain
authors.affiliation: Department of Urology, Indiana University School of Medicine, Riley Hospital for Children, 705 Riley Hospital Drive, Room 4230, Indianapolis, IN 46202, USA. Electronic address: rrink@iupui.edu.
authors.forename: R C
authors.initials: RC
authors.lastname: Rink
authors.affiliation: Department of Radiology and Imaging Sciences, Indiana University School of Medicine, 950 W. Walnut Street, Room E124, Indianapolis, IN 46202, USA. Electronic address: sajennin@iupui.edu.
authors.forename: S G
authors.initials: SG
authors.lastname: Jennings
authors.affiliation: Department of Urology, Indiana University School of Medicine, Riley Hospital for Children, 705 Riley Hospital Drive, Room 4230, Indianapolis, IN 46202, USA. Electronic address: mkaefer@iupui.edu.
authors.forename: M
authors.initials: M
authors.lastname: Kaefer
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D052177:Kidney Diseases, Cystic / Q000145:classification* / Q000000981:diagnostic imaging* / Q000628:therapy; D008297:Male; D015588:Observer Variation; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014463:Ultrasonography
keywords: Children; Complex cysts; Simple cysts; Solitary renal cysts; Ultrasound