The vascular "ring" sign in mesoblastic nephroma: report of two cases.

Mesoblastic nephroma (Bolande's tumour) is a rare renal tumour, but, overall, is the most frequent benign renal tumour in childhood and the most frequent renal tumour during the first year of life. It is increasingly diagnosed with US during the fetal period. We report the findings of two patients who showed the "ring" sign, an anechoic ring surrounding the tumour and typical of mesoblastic nephroma. We identified a Doppler signal in the ring in both cases, and pathology confirmed the vascular origin of this sign.