Calyceal crescents (of Dunbar and Nogrady)

Excerpt

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].

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