To evaluate the sonographic involution of prenatally detected multicystic dysplastic kidney (MCDK).

A total of 53 children with unilateral MCDK detected by prenatal ultrasonography between 1989 and 2004 were included in this analysis. All children received conservative management with follow-up visits every 6 months. Follow-up ultrasound examinations were performed at 6-month intervals during the first 2 years after birth and yearly thereafter. A linear mixed effect model was constructed, including MCDK length as the dependent variable and body size parameters and contralateral renal dimensions as independent variables.

The mean follow-up time was 68 months. A total of 334 ultrasound scans were analyzed. The ultrasound scan demonstrated partial or total involution of the MCDK in 48 cases (91%). A consistent negative correlation was found among MCDK length, patient age, and body size parameters. As a whole, the MCDK length reduction was estimated to be 0.29 mm/mo. The rate of reduction was not constant over time and was intense during the first 30 months of age. According to the regression model, MCKD reduced in length by 0.80 mm/mo during the first 30 months of age, 0.26 mm between 30 and 84 months old, and 0.30 mm in children older than 84 months.

Our results suggest a clear tendency of MCDK to decrease in size, with the rate of the involution greater during the first 30 months than the rate in older children.