Stipple sign | Radiology Signs

Answer:

The stipple sign is the punctate, dotted pattern of contrast trapped within the interstices of a frond-like papillary urothelial tumour, seen within an otherwise lucent filling defect in the renal pelvis or ureter on intravenous urography, retrograde pyelography or the excretory phase of CT urography. Contrast insinuates between the villous fronds of the tumour and produces multiple small dots on the surface of the defect, which is a strong indicator that the defect is a papillary urothelial carcinoma rather than a stone or clot. The two competing causes of a lucent filling defect behave differently: a radiolucent calculus is smooth, sharply marginated, mobile and, decisively, shows high attenuation on unenhanced CT; a blood clot is also non-enhancing but is of high attenuation before contrast, changes shape or resolves on follow-up imaging, and lacks fronds. Tumour, by contrast, is fixed, has an irregular frond surface and enhances, typically by 20 HU or more, which is why a properly performed CT urogram with unenhanced, nephrographic and excretory phases has replaced conventional urography for this problem. Upper tract urothelial carcinoma is often multifocal and mandates evaluation of the entire urothelium including the bladder, and it is associated with Lynch syndrome, aristolochic acid exposure and heavy smoking. Ureteroscopy with biopsy and selective cytology remains necessary for confirmation and grading.

Why is it called so?

Contrast caught in the crevices of the tumour surface produces a stippled or speckled pattern, as though the lesion had been dotted with ink.

Pathophysiology

Papillary urothelial carcinoma grows as delicate fronds of neoplastic urothelium supported by fibrovascular cores that project into the collecting system lumen. The spaces between adjacent fronds are narrow and communicate with the lumen, so opacified urine fills them and is retained there while surrounding urine drains, producing discrete pools of contrast on the tumour surface. Because the fronds are attached to the wall the mass does not move with position change, unlike a calculus, and because it has a vascular stroma it enhances after intravenous contrast, unlike clot. Slow growth within the ureter also allows the wall to dilate around it rather than obstruct abruptly, which is the basis of the related goblet sign.

Alternative names: Stippled appearance of a urothelial filling defect

Other associated named signs: Goblet sign or champagne glass sign of the ureter distal to a slow-growing tumour, and the phantom calyx of infundibular obstruction

References

1. Nakai H, Takahashi H, Wellnitz CV, Stanton ML, Takahashi N, Kawashima A. Imaging of Upper Tract Urothelial Carcinoma. Radiographics. 2024;44(11):e240056. PMID: 39480700.