Detailed evaluation of the upper urinary tract in patients with prune belly syndrome using magnetic resonance urography.

INTRODUCTION: Magnetic resonance urography (MRU) has proven to be useful in the setting of complex urologic anatomy. Prune belly syndrome (PBS) patients are known to have malformed and highly variable urinary tract anatomy due to significant dilation and renal dysplasia.

OBJECTIVE: To further characterize the renal and ureteral anatomy and renal function in patients with PBS via MRU.

STUDY DESIGN: Children with PBS undergoing MRU (2006-2011) were identified. Studies were performed to evaluate severe hydronephrosis in all patients. Demographics, previous imaging, and MRU findings were collected. A single radiologist reviewed all studies.

RESULTS: MRU was performed on 13 boys, with a median age of 29.3 months (IQR 6-97). Two patients underwent >1 study for ureteropelvic junction obstruction (UPJ obstruction) and calyceal diverticulum with a solitary kidney, respectively. Hydroureteronephrosis (HUN) was identified in 12 boys (92%), while one (8%) did not have ureteral dilation. All patients demonstrated morphologic abnormalities beyond HUN as follows: five (38%) renal dysplasia; five (38%) scarring; four (31%) calyceal diverticula; and three (23%) thickened bladder. The median renal transit time (RTT) was 6 min (IQR 3.5-10.5), and >8 min (range 8.5-35) in six patients; one patient was ultimately diagnosed with obstruction. The mean serum creatinine was 0.5 ± 0.3 mg/dl. This summary figure is a coronal excretory phase T1 MRU image demonstrating absence of well-defined calyces and a 5-cm calyceal diverticulum (white arrow).

DISCUSSION: This study reports significant anatomic and functional findings on MRU that were not readily apparent when using standard imaging for children with PBS. The high-resolution images and functional data obtained with MRU allowed for visualization of calyceal diverticula and abnormal renal pelvic anatomy not previously described in PBS. In addition, renal dysplasia could be identified with MRU, which is badly characterized in the PBS population outside of renal biopsy studies. Potential limitations of the study included its nature as a small retrospective case series, which limited the ability to compare imaging modalities. Imaging modalities were based on individual clinical needs; therefore, comparison with diuretic renal scintigraphy was limited.

CONCLUSION: MRU provided anatomic and functional details of the urinary tract in children with PBS that allowed for characterization of new renal anatomic abnormalities, including the incidence of calyceal diverticula and renal dysplasia, which have not been previously described. While renal scarring, dysplasia and calyceal diverticula were easily discerned on MRU in ten patients, their clinical significance requires longer follow-up in a larger patient population.