Purpose or Case Report: Lower moiety hydronephrosis/ureteropelvic junction (UPJ) obstruction is an uncommon configuration of duplex collecting systems. We sought to characterize its prevalence, appearance and behavior using diuresis renograms (DR).
Methods & Materials: From an IRB-approved database of 2,025 patients with DR performed over a 23-year period, cases of hydronephrosis of the lower moiety of duplex collecting system were identified. Cases with hydroureter, vesicoureteral reflux, and those without follow-up were excluded. Clinical presentation, kidney function and post-furosemide drainage parameters on initial and follow-up DR, as well as outcome data regarding non-obstructive drainage requiring no further follow-up, and obstruction necessitating surgical intervention were reviewed.
Results: Twenty-one kidney units (KU) were identified in 20 patients (13 male, 7 female), including one patient with bilateral duplex systems, for a prevalence of 0.99%. Median age was 0.36 years (range 0.04 to 17.8 years). 14 patients (70%) presented with antenatal hydronephrosis and 6 patients (30%) with abdominal/flank pain, including 2 with co-existing urinary tract infection. 7 were right-sided, 14 were left-sided, 5 partial and 16 complete duplex systems; 20/21 had normal renal function and maintained renal function on follow-up. Mean follow-up period for all patients was 25.1 months. 11 patients had more than one DR. 11 KUs had non-obstructive drainage, 5 upon initial DR and 6 on follow-up. 10 KU’s had obstructed drainage requiring surgery, 5 upon initial DR and 5 on follow-up.
Conclusions: Hydronephrosis of the lower moiety of a duplex system is rare; nearly half of the cases have UPJ obstruction requiring surgical intervention. While most are diagnosed antenatally, almost one third present with abdominal/flank pain. Almost all have normal renal function. Diuresis renography is a valuable tool for the diagnosis and management of this rare clinical entity.