Nephrogenic remnants: occasional ultrasound diagnosis and follow-up.

Nephrogenic remnants (NRs) are nodular collections of undifferentiated renal blastema cells in the postnatal kidney that are recognized as putative precursor lesions of Wilms tumor (WT). NRs may remain stationary, undergo regression, or proliferate. In the last case, there is a high risk for the development of a WT. During infancy, they are most frequently of microscopic size, to be found only at autopsy in approximately 1% of infant kidneys. Approximately 1 out of 100 microscopic lesions persist and grow developing lesions large enough to be seen by ultrasound in the first months of life. We report on a case of NRs in a six year old child, as incidental finding during abdominal ultrasound performed for other purposes. In consideration of the potential evolution in WT, after a period of close surveillance of 14 months, the lesion was resected. Histological examination revealed the presence of NRs, no neoplastic lesions were found. Currently the patient is 16 years old, in good health, and there have been no signs of recurrence.