Mild fetal renal pelviectasis. Differentiation from hilar vascularity using color Doppler sonography

Ultrasound often detects a sonolucent region in the hilum of the fetal kidney. Although this sonolucency is usually assumed to represent mild dilatation of the fetal renal collecting system, in pediatric and adult kidneys blood vessel lumina can simulate pelviectasis. We used color Doppler ultrasound to differentiate the fetal renal collecting system from hilar blood vessels and to evaluate how often blood vessels account for the sonolucent region often demonstrated in the renal hilum during antenatal sonography. Twenty-nine kidneys in fetuses with sonolucent hilar regions greater than 2 mm in anteroposterior (AP) dimension were studied with color Doppler ultrasound. Doppler signal was demonstrated in blood vessels adjacent to, but not within, the sonolucent area in the hilum of all 29 kidneys. Based on the absence of color signal in the sonolucent hilar regions studied, with color signal seen in adjacent blood vessels, these regions were felt to represent mildly dilated collecting systems rather than renal vasculature. We conclude that color Doppler ultrasound can differentiate mild pelviectasis from hilar blood vessels in the fetal kidney. Sonolucent areas measuring 2 mm or greater in AP dimension are unlikely to be attributable to renal vasculature.