Published in:
01-01-2019 | Classics in Abdominal Radiology
Calyceal crescents (of Dunbar and Nogrady)
Published in: Abdominal Radiology | Issue 1/2019
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In the presence of chronic hydronephrosis, the normal vertical orientation of collecting tubules in the renal medulla may be altered by progressive dilatation of the calyx [1]. The positional change in the tubules, such that they lie parallel to the margin of the dilated calyx as opposed to their normal vertical orientation in the medulla, may produce a “crescent” shape when the tubules are opacified with concentrated contrast material (Fig. 1). Although originally described at conventional excretory urography [1], the appearance may also be seen during CT urography (Fig. 2A–C). The calyceal crescent sign is seen early in the course of the contrast examination and fades as the dilated collecting system becomes opacified [1, 2].
Fig. 1
Vintage shutters with crescent moon-shaped carvings
Fig. 2
A Unenhanced axial CT image demonstrates severe hydronephrosis involving the upper pole of the right kidney. The dilated collecting system contains a small stone (arrow). B Early excretory phase image shows unopacified urine in the dilated upper pole collecting system. C Delayed image obtained with the patient prone shows a thin “crescent” of contrast material along the posterior aspect of the dilated collecting system (arrows), which is now partially opacified
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