title: Keyhole sign: how specific is it for the diagnosis of posterior urethral valves?
abstract: OBJECTIVE
  Posterior urethral valves (PUV) are the most common cause of renal impairment in boys during early childhood. Although antenatal suspicion of this pathology has become quite common in recent years, prenatal diagnosis remains challenging. The aim of this study was to evaluate the predictive value of different ultrasound criteria currently used to diagnose PUV.
  
  
  METHODS
  We reviewed the antenatal and postnatal files of 54 male patients referred to our center from 2000 to 2006 after detection of fetal bilateral hydronephrosis. The following ultrasound criteria were evaluated in relation to the postnatal diagnosis of PUV: amniotic fluid volume, bladder wall thickness, bladder dilatation and the presence of the 'keyhole sign'.
  
  
  RESULTS
  Forty-two fetuses (77.8%) were suspected to have PUV on prenatal examination. Out of these, 29 (69.0%) had PUV confirmed postnatally. The sensitivity and specificity of the antenatal diagnosis of PUV were 94% and 43%, respectively. Increased bladder wall thickness and bladder dilatation were highly associated with the diagnosis of PUV (P < 0.001). However, a thick-walled bladder was observed in 39.1% and a dilated bladder in 47.8% of the infants with a postnatal diagnosis other than PUV. The presence of the keyhole sign was not found to predict a diagnosis of PUV (P = 0.27).
  
  
  CONCLUSIONS
  In this series the use of classical prenatal ultrasound signs to diagnose PUV showed high sensitivity but low specificity. The best diagnostic indicators were increased bladder wall thickness and dilatation of the bladder. The keyhole sign was not found to be a reliable predictor of PUV.
authors.affiliation: Maternité, Université Paris Descartes, Faculté de Médecine, AP-HP, Hôpital Necker-Enfants Malades, Paris, France. lisbernardes@usp.br
authors.forename: L S
authors.initials: LS
authors.lastname: Bernardes
authors.forename: G
authors.initials: G
authors.lastname: Aksnes
authors.forename: J
authors.initials: J
authors.lastname: Saada
authors.forename: V
authors.initials: V
authors.lastname: Masse
authors.forename: C
authors.initials: C
authors.lastname: Elie
authors.forename: Y
authors.initials: Y
authors.lastname: Dumez
authors.forename: S L
authors.initials: SL
authors.lastname: Lortat-Jacob
authors.forename: A
authors.initials: A
authors.lastname: Benachi
mesh_terms: D005260:Female; D005865:Gestational Age; D006801:Humans; D006869:Hydronephrosis / Q000000981:diagnostic imaging* / Q000196:embryology; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D011256:Pregnancy Outcome; D011379:Prognosis; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal; D014521:Urethra / Q000002:abnormalities / Q000000981:diagnostic imaging* / Q000196:embryology; D001743:Urinary Bladder / Q000002:abnormalities / Q000000981:diagnostic imaging* / Q000196:embryology