The “stipple sign”

Excerpt

The “stipple” sign describes the unique appearance of a papillary urothelial neoplasm when contrast material in the urinary tract becomes trapped between the papillary projections. The contrast material creates a pattern of tiny dots when viewed en face (Fig. 1a, b) [1‐3], similar to the pattern produced by the artistic technique of stippling (Fig. 2). This uncommon finding was originally described at excretory urography [1], but the pattern can be translated to CT and MR urography. Though fungus balls, and occasionally blood clots, can trap contrast material within their interstices, the pattern tends to be coarser with blood clots and may assume a lamellar appearance with fungus balls [1].

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