"The stipple sign refers to the pointillistic end-on appearance on intravenous pyelography or retrograde pyelography of contrast material tracking into the interstices of a papillary lesion. Because the majority of urothelial carcinomas have a papillary configuration, the presence of this sign should raise the suspicion of UC. While the stipple sign is best seen in large papillary bladder tumours, it can occur anywhere a urothelial tumour expresses papillary architecture."
"Be aware, however, that the stipple sign may also be seen with blood clots and fungus balls, and is not pathognomonic for UC."