The Crescent Sign

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Abstract
In 1962, Dunbaret al. (1) reported a “crescent” sign in hydronephrosis. This sign was attributed to the contrast material in collecting tubules that had changed their orientation by approximately 90 degrees so as to lie parallel to the renal convexity and close to its surface. This change in orientation is caused by increased pressure in the renal collecting system and is seen only in severe hydronephrosis. It is detectable during the early phases of intravenous pyelography and then disappears as calyces and pelvis are opacified. It is our purpose to present a case of hydronephrosis secondary to ureteropelvic stricture that appears to document Dunbar's explanation for the crescent sign. Case Report J. H. B., a 4-month-old white male, was hospitalized Jan. 4, 1963, because of an upper respiratory infection of ten days duration. The mother reported the presence of a protuberant abdomen since birth and an abdominal mass observed for the first time on the day of admittance. Physical examination revealed a well developed child. The only finding of note was a smooth, cystic mass, slightly mobile, in the right flank extending to the midline. Blood-urea-nitrogen was 25. On intravenous pyelography the initial film showed a large soft-tissue mass in the right side of the abdomen, displacing air-filled structures to the left. Renal outlines could not be visualized. Early films demonstrated crescentic collections of contrast material distributed around the periphery of the right kidney (Figs. 1 and 2). The study was continued for forty minutes. During this time the crescents almost completely disappeared, without opacification of any other structures. The left kidney was hydronephrotic. A diagnosis of either Wilms's tumor or renal cyst was made, with medial extension and compression of the left ureter. The crescents were thought to represent distorted calyces. Cystoscopy revealed a normal bladder and patulous ureteral orifices. Clear urine came from the left ureter but no function was seen on the right side. On Jan. 11, a right nephrectomy was performed. The kidney was huge, cystic in nature, and contained 1,000 c.c. of clear fluid. Examination of the specimen revealed marked hydronephrosis caused by redundant, valve-like mucosal folds at the ureteropelvic junction. Renal substance was atrophic and residual normal parenchyma was found distributed around the periphery of the hydronephrotic sac, especially at its superolateral border. Subsequent intravenous pyelography has revealed increasing hydronephrosis on the left because of ureteropelvic obstruction. Discussion Re-evaluation of the initial intravenous pyelogram disclosed that the crescentic collections of contrast material could not have been distorted calyces, all of which were found to be grossly hydronephrotic.

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