O2220: Posterior Urethral Valves with a Multilocular Cystic Nephroma: a case report

Introduction: Posterior urethral valves (PUV) are congenital urinary tract outflow abnormalities that cause lower urinary tract obstruction in male infants, occurring in approximately 1 in 3,000 to 1 in 8,000 live male births. PUV can cause significant morbidity, including urinary tract infections (UTIs), hydronephrosis, and long-term renal impairment. Multilocular cystic nephroma (MLCN) is a rare, benign renal neoplasm accounting for roughly 2% of pediatric renal tumors, typically presenting in male children under two years of age. While both conditions are individually recognized in pediatric urology, their co-occurrence is exceedingly rare. MLCN has been linked to mutations in the DICER1 gene, which is associated with a range of benign and malignant neoplasms. Here, we present a unique case of a 7-month-old male with coexisting PUV and MLCN who tested positive for a germline DICER1 mutation.

Case Description: The patient, a 7-month-old male, was transferred to Nemours Children’s Health shortly after birth due to antenatal findings of right hydronephrosis and postnatal imaging showing bilateral hydroureteronephrosis. He was born at term via cesarean section to a 42-year-old mother with insulin-managed diabetes mellitus. PUV was diagnosed via voiding cystourethrogram (VCUG), and the patient underwent transurethral ablation of the valves shortly after birth. Imaging during treatment for a febrile UTI, 10 weeks after birth, incidentally revealed an abnormal cystic lesion in the lower pole of the right kidney which was measured to be 1.6x1.8x1.5 cm and initially thought to be segmental renal dysplasia. However, follow-up imaging 4 months later showed rapid lesion growth to 5.8x5.8x5.5 cm. The rapid growth of the mass right warranted surgical intervention and radical nephrectomy was recommended. MRI findings 1 month later demonstrated continued growth (6.7x6.9x6.3 cm) and raised suspicion for MLCN. The patient underwent right radical nephrectomy and repeat cystoscopy. At repeat cystoscopy residual valves were revealed and ablated. Histopathology confirmed MLCN. Given the tumor type, DICER1 testing was performed and returned positive. Postoperative imaging revealed stable hydroureteronephrosis of the remaining kidney.

Discussion: The coexistence of PUV and MLCN, particularly in the context of a positive DICER1 mutation, is exceptionally rare and not previously reported in the literature. Imaging played a critical role in both initial diagnosis and in identifying the renal mass. Although MLCN is benign, rapid growth and indistinguishability from malignancy preoperatively necessitate surgical excision. The persistence of hydronephrosis in the contralateral kidney underscores the importance of long-term surveillance, especially given the increased risk of renal dysplasia in patients with PUV and solitary kidneys.

Conclusion: This case represents the first known report of coexisting PUV and MLCN in a DICER1-positive patient. It highlights the importance of multidisciplinary care, the role of genetic evaluation in rare pediatric tumors and the need for vigilant long-term follow-up in patients with congenital urologic anomalies and genetic predispositions.