Configuration and validation of the Toronto Nomogram of Antenatal Ultrasound Index generated from Bayesian meta-regression analysis in predicting posterior urethral valves
Jin Kyu (Justin) Kim1,2, Michael Chua1,2, Armando Lorenzo1,2, Tim Van Mieghem3, Eric Mackay1, Lauren Erdman1, Marta Skreta1, Daniel T. Keefe1, Marisol Lolas1, Priyank Yadav1, Joana Dos Santos1, Mandy Rickard1.
1Division of Urology, Department of Surgery, University of Toronto, Toronto, ON, Canada; 2Division of Urology, The Hospital for Sick Children, Toronto, ON, Canada; 3Division of Maternal Fetal Medicine, Mount Sinai Hospital, Toronto, ON, Canada
Introduction: The keyhole sign is considered to be suggestive of a postnatal diagnosis of posterior urethral valve (PUV). However, not all fetuses with PUV may have this feature, potentially leading to missed diagnoses and symptomatic postnatal presentation. Herein, we configured a nomogram to assess the diagnostic accuracy of the nomogram in comparison to the keyhole sign in predicting a postnatal diagnosis of PUV.
Methods: Antenatal ultrasound indices identified by the Bayesian meta-regression analysis that were highly predictive of PUV were oligohydramnios, bilateral hydronephrosis, bilateral ureteral dilatation, megacystis, bladder thickening, and urinoma. The nomogram was configured as a calculator with the baseline 6% PUV incidence among male fetus with moderate-severe hydronephrosis. The pooled diagnostic odds ratio generated for each diagnostic index was used as a coefficient factor for nomogram configuration to calculate the probability of PUV. The nomogram was validated using our institutional prenatal consultation database (March 2020 to present).
Results: Based on 72 antenatal consults for male infants with moderate to severe hydronephrosis, the keyhole sign has a specificity of 100% and sensitivity of 44%, while the nomogram had specificity of 96.83 and sensitivity of 100%. The keyhole sign had two false negatives and the nomogram had two false positives. The receiver operating characteristic curve showed that the nomogram had a superior area under the curve compared to the keyhole sign (Figure 1). The suggested cutoff using Youdin's index for the nomogram was 95% probability to prevent false positives. The NNS was 2.42 for keyhole sign and 1.03 for our nomogram.
Conclusions: Based on the validation study, we have established that the Toronto Antenatal Ultrasound Indices nomogram calculator for PUV has similar if not better diagnostic accuracy with keyhole sign. The nomogram can be an adjunctive tool to trigger additional post-natal screening for patients who do not present with classic keyhole sign but have high index of suspicion.
