3DUS as an alternative to MRI for measuring renal volume in children with autosomal dominant polycystic kidney disease

Background: Total kidney volume, measured by magnetic resonance imaging (MRI), is a validated disease progression marker in adults with autosomal dominant polycystic kidney disease (ADPKD). However, in childhood, MRI is burdensome, explaining the need for alternatives.

Methods: Kidney volume (KV) was evaluated in 30 children with ADPKD, using three-dimensional ultrasound (3DUS), applying the ellipsoid method and manual contouring (KV_{3DUS-ellipsoid,} KV_3DUS-contour respectively); manual contouring on MRI (KV_MRI), and the ellipsoid method on two-dimensional ultrasound (2DUS, KV_2DUS). Correlations and differences were evaluated using Pearson's r and Wilcoxon signed-rank tests, and variability using Bland-Altman plots.

Results: All ultrasound volumetry methods showed significantly lower mean (± SD) KV (mL), compared with MRI-KV_2DUS: 159 (±101); K_{3DUS-ellipsoid}: 169 (±105); KV_3DUS-contour: 185 (±110); KV_MRI: 206 (±130); all p < 0.001. All had a strong correlation with KV_MRI: 2DUS: r = 0.96; 3DUS-ellipsoid: r = 0.89 and 3DUS-contour: r = 0.94. Both before and after correction factor application, Bland-Altman plots showed lower variability and absolute error for KV_3DUS-contour vs KV_2DUS and KV_{3DUS-ellipsoid}.

Conclusions: Compared with MRI, ultrasound volumetry was prone to underestimation. However, KV_3DUS-contour represents a valuable alternative for MRI in early ADPKD. Although more time-consuming, KV_3DUS-contour is recommended over KV_2DUS for estimation and follow-up of KV in ADPKD children, given its smaller error.