Diagnostic Test Characteristics of Renal Ultrasound Findings for High-Risk Bladder in Spina Bifida

INTRODUCTION: Spina bifida (SB) can cause neurogenic bladder dysfunction and renal deterioration. Guidelines recommend renal ultrasound (RUS) for surveillance, but its utility in screening for high-risk bladder is unclear. We evaluated the performance of RUS findings for detecting high-risk bladder in youth with SB. MATERIALS AND METHODS: We conducted a retrospective cohort study of patients with myelomeningocele at a pediatric SB clinic who had a RUS within three months of urodynamic studies (UDS). RUS parameters included hydronephrosis, thinned parenchyma, hypoplasia, and scarring. High-risk bladder was defined as end-fill pressures/detrusor leak point pressures of 40 cmH2O or greater. We calculated sensitivity, specificity, and overall diagnostic accuracy (AUC) of RUS parameters for high-risk bladder, adjusting for repeat measurements. Various subgroup and sensitivity analyses were performed. RESULTS: We analyzed 575 UDS-RUS dyads from 244 unique patients. Median age was 7.2 years, 70% had ventricular shunts. 25% of dyads had high-risk bladder. Any hydronephrosis by Society for Fetal Urology (SFU) grading demonstrated an overall sensitivity 50%, specificity 57%, and clustered AUC of 55% for detecting high-risk bladder. RUS had similar performance across additional analyses, including non-ambulatory patients, high-grade hydronephrosis (SFU 3-4), any RUS abnormality, and using Urinary Tract Dilation (UTD) grading instead of SFU grading. Any hydronephrosis had higher test sensitivity for high-risk bladder in fuller bladders on RUS (RUS-bladder volume >75% of UDS-bladder capacity). CONCLUSION: RUS should not be used alone as a screening tool to identify high-risk bladder in youth with SB given its limited sensitivity and diagnostic utility. UDS remains an essential and necessary tool for surveilling at-risk bladders.