Dysplastic kidney and not renal agenesis is the commonly associated anomaly in infants with seminal vesicle cyst.

To determine whether the association of seminal vesicle cyst (SVC) and renal anomaly in young children correlates with previously reported cases of SVCs in adolescent and adult patients, as congenital SVCs, although rare, are frequently described in association with ipsilateral renal agenesis, mainly in adolescent and adult patients, whereas reports on SVCs in younger children are sparse. We report on nine infants (median age 4 months) with congenital SVCs, all of them associated with ipsilateral dysplastic kidneys. All patients had ultrasonography of the renal system and voiding cysto-urethrography. Magnetic resonance imaging was used in two patients. The SVCs were found incidentally during ultrasonography for the renal anomaly. Three patients had dysplastic and six had multicystic dysplastic kidneys. In previous reported adult cases of SVCs the most common associated renal anomaly was agenesis of the ipsilateral kidney (25 of 44 cases), whereas only one case of dysplastic kidney was reported. As the appearance of renal agenesis might result from a former congenital dysplastic kidney, our findings indicate that cases of ipsilateral renal agenesis in adult patients with congenital SVCs might represent former dysplastic or multicystic dysplastic kidney.