title: Presence of the eggshell sign in obstructive uropathy.
abstract: OBJECTIVE
  To analyze the relationship between hydronephrosis due to urinary tract obstruction and the presence of the sonographic eggshell sign, which is a recently described crescent of increased echogenicity at the caliceal/parenchymal interface and possibly an indicator of raised intrarenal pressure.
  
  
  METHODS
  All patients presenting between 1996 and 1999 for surgical management of pelviureteral junction obstruction or congenital posterior urethral obstruction had films reviewed for the presence of the eggshell sign.
  
  
  RESULTS
  Of 94 patients, 40 presented postnatally and 54 had hydronephrosis detected on the antenatal ultrasound scan. Of the postnatal group, 16 (40%) had urethral obstruction, of whom 4 (25%) displayed the eggshell sign; in the 24 with pelviureteral junction obstruction, the echogenic pericaliceal crescent was seen in 5 (20.8%). Of the 54 in the prenatal group, 8 (15.4%) were found to have urethral obstruction, 5 (62.5%) of whom demonstrated the eggshell sign. Of the 46 prenatally diagnosed patients with pelviureteral junction obstruction, 31 (70.5%) displayed the eggshell sign before birth; we were unable to satisfactorily review 2 patients' ultrasound scans.
  
  
  CONCLUSIONS
  Antenatally diagnosed hydronephrosis due to significant urinary tract obstruction seems to be related to the appearance of the eggshell sign on ultrasonography, particularly in those patients with pelviureteral junction obstruction. Those patients without significant caliceal distension and those with renal dysplasia or severe hydronephrosis with low-pressure kidneys were less likely to display the eggshell sign. Although the association with other causes of hydronephrosis is unknown, we believe these figures support the need for further investigation of the eggshell sign as a marker of raised intrarenal pressure to possibly provide another data point in the sonographic evaluation of congenital hydronephrosis.
authors.affiliation: Urology Unit, Royal Children's Hospital, Melbourne, Victoria, Australia.
authors.forename: P A
authors.initials: PA
authors.lastname: Dewan
authors.forename: D
authors.initials: D
authors.lastname: Moon
authors.forename: K
authors.initials: K
authors.lastname: Anderson
mesh_terms: D006801:Humans; D006869:Hydronephrosis / Q000151:congenital* / Q000000981:diagnostic imaging; D011446:Prospective Studies; D014463:Ultrasonography; D014517:Ureteral Obstruction / Q000000981:diagnostic imaging*