Development of the hypodysplastic kidney: contribution of antenatal US diagnosis.

Two cases of fetal perirenal uriniferous pseudocyst were diagnosed in utero with ultrasound studies. The perirenal collections resolved spontaneously in utero. Follow-up examination showed growth impairment of the affected kidney. At birth, no renal function was demonstrated in one case and only slight function in the other case. Pathologic examination showed a highly dysplastic kidney with extravasated urine in the case in which surgery was performed. Some hypodysplastic kidneys apparently result from acute in utero obstruction with secondary pyelocalyceal rupture. Renal dysplasia could render the kidney more vulnerable to such phenomena.