title: Computerized tomography attenuation values can be used to differentiate hydronephrosis from pyonephrosis.
abstract: OBJECTIVE
  To determine the diagnostic value of computerized tomography (CT) in differentiating pyonephrosis from hydronephrosis on the basis of attenuation values (Hounsfield unit-HU).
  
  
  METHODS
  Data of the patients with grades 1-3 hydronephrosis on abdominopelvic CT, who underwent nephrostomy tube placement for decompression of the collecting system, were retrospectively analyzed. Patient demographics and CT findings were recorded along with the first access urine culture results. Three physicians calculated the surface areas and the attenuation values of the dilated collecting systems using the system software. Mean HU of pyonephrosis and hydronephrosis cases was compared.
  
  
  RESULTS
  A total of 105 patients with the mean age of 47.7 ± 15.5 (range 20-80) were included. The interclass correlation coefficient of three physicians was 0.981 for HU measurement and 0.999 for calculation of collecting system surface area. Of the patients, 47 (44.8 %) had pyonephrosis. Mean surface areas of the collecting system were similar in patients with pyonephrosis and hydronephrosis (1481.13 ± 1562.94 vs. 1612.94 ± 2261.4 mm2, p = 0.735). Urine cultures were positive in all patients with pyonephrosis, whereas 12.7 % of hydronephrosis cases had bacterial in first access urine culture. The HU of the patients with pyonephrosis was significantly higher that that of patients with hydronephrosis (13.51 ± 13.29 vs. 4.67 ± 5.37, p = 0.0001). Having a HU of 9.21 or over diagnosed pyonephrosis accurately with 65.96 % sensitivity and 87.93 % specificity.
  
  
  CONCLUSIONS
  Measuring attenuation values of the collecting system may be useful to differentiate pyonephrosis from hydronephrosis. Diagnosing pyonephrosis accurately may avoid septic complications.
authors.affiliation: Department of Urology, Bagcilar Training and Research Hospital, Istanbul, Turkey. emrah.yuruk@yahoo.com.
authors.forename: Emrah
authors.initials: E
authors.lastname: Yuruk
authors.affiliation: Department of Urology, Bagcilar Training and Research Hospital, Istanbul, Turkey.
authors.forename: Murat
authors.initials: M
authors.lastname: Tuken
authors.affiliation: Department of Urology, Bagcilar Training and Research Hospital, Istanbul, Turkey.
authors.forename: Suhejb
authors.initials: S
authors.lastname: Sulejman
authors.affiliation: Department of Urology, Bagcilar Training and Research Hospital, Istanbul, Turkey.
authors.forename: Aykut
authors.initials: A
authors.lastname: Colakerol
authors.affiliation: Department of Urology, Bagcilar Training and Research Hospital, Istanbul, Turkey.
authors.forename: Ege Can
authors.initials: EC
authors.lastname: Serefoglu
authors.affiliation: Department of Urology, Kartal Training and Research Hospital, Istanbul, Turkey.
authors.forename: Kemal
authors.initials: K
authors.lastname: Sarica
authors.affiliation: Department of Urology, Bagcilar Training and Research Hospital, Istanbul, Turkey.
authors.forename: Ahmet Yaser
authors.initials: AY
authors.lastname: Muslumanoglu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001437:Bacteriuria / Q000150:complications / Q000175:diagnosis*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D006869:Hydronephrosis / Q000150:complications / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009403:Nephrostomy, Percutaneous; D053018:Pyonephrosis / Q000175:diagnosis / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: Attenuation value; Computerized tomography; Hounsfield unit; Hydronephrosis; Pyonephrosis