Inter-rater reliability of postnatal ultrasound interpretation in infants with congenital hydronephrosis

The most common measurements of hydronephrosis are the anterior-posterior (AP) diameter and the Society for Fetal Urology (SFU) grading systems. To date, the inter-rater reliability (IRR) of these measures has not been compared in the postnatal period. The objectives of this study were to compare the IRR of the AP diameter and the SFU grading system in infants and to determine whether ultrasound findings other than pelvicalyceal dilation are associated with higher SFU grades.

Initial postnatal ultrasounds of infants seen from February 1, 2011, to January 31, 2012, with a primary diagnosis of congenital hydronephrosis were included for review. Ultrasound images were de-identified and reviewed by four pediatric urologists. IRR was calculated using the intraclass correlation (ICC) measure. A paired t test was used to compare ICCs. Associations between SFU grade and other ultrasound findings were tested using Chi-square or Fisher's exact tests.

A total of 112 kidneys in 56 patients were reviewed. IRR of the SFU grading system was high (right kidney ICC = 0.83, left kidney ICC = 0.85); however, IRR of AP diameter measurement was higher (right kidney ICC = 00.97, left kidney ICC = 0.98; p < 0.001). Renal asymmetry (p < 0.001), echogenicity (p < 0.001), and parenchymal thinning (p < 0.001) were significantly associated with SFU grade 4 hydronephrosis on bivariable and multivariable analysis.

The SFU grading system is associated with excellent IRR, although the AP diameter appears to have higher IRR. Physicians may consider ultrasound findings that are not explicitly included in the SFU system when assigning hydronephrosis grade, which may lead to variability in use of this classification system.