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To the Editor:—
The article "Perirenal Contrast Medium" (193:1121, 1965), in which Dockray describes a new roentgenographic sign of neonatal urinary ascites, is of interest. The distinctive roentgenographic halo sign is explained by transudation or extravasation of opacified urine from the kidney into the retroperitoneal space and is described as a perirenal halo. It would appear to us from the roentgenogram that the peripheral nephrogram effect of hydronephrosis as described by Allen et al (Radiology80:203, 1963) is the responsible mecha[ill]m. According to these authors, the nephrogram represents compressed functioning renal parenchyma. Variations of this principle which grossly dilated calyces formed "the crescent sign" were described by Dunbar et al in 1962.LeVine et al (Radiology81:971, 1963) suggested that the crescent sign histologically appeared to be due to retention of contrast material in dilated peripherally displaced renal tubules. The halo sign as described by Dockray
Keeffe EJ, Harrow BR. Hydronephrosis or Neonatal Urinary Ascites. JAMA. 1965;194(9):1024. doi:10.1001/jama.1965.03090220080036