Kidney volume estimations with ellipsoid equations by magnetic resonance imaging in autosomal dominant polycystic kidney disease.

BACKGROUND Kidney volume (KV) becomes clinically relevant in autosomal dominant polycystic kidney disease (ADPKD) management. KV can be conveniently estimated (ceKV) using ellipsoid volume equations with three axes measurements; however, the accuracy and reliability are unknown. METHODS KVs of 347 kidneys in 177 consecutive ADPKD patients were determined with a volumetric method (standard-KV), and ceKV was calculated using six different ellipsoid equations with three axes measurements using magnetic resonance imaging. The inter- and intraobserver reliabilities were analyzed using intraclass correlation coefficients (ICCs). Ellipsoid-KVs were obtained by linear regression analysis between standard-KV and ceKVs, and six ellipsoid-KVs were validated with a bootstrap model. RESULTS The ICCs of intra- and interobserver reliabilities in standard-KV and axes measurements were highly reliable. All ceKVs underestimated standard-KV and % differences between ceKV and standard-KV were reduced by ellipsoid-KVs. Bootstrap analyses suggested that six ellipsoid-KVs reliably simulated standard-KV. CONCLUSION Among six ellipsoid-KVs, ellipsoid-KV3 = 84 + 1.01 x π/24 × Length × (sum of two width measurements)(2) relatively accurately simulated the standard-KV. Kidney volume estimation using ellipsoid equations is reliably applied to clinical management of ADPKD while recognizing wide scattering in the difference between estimated and volumetrically measured kidney volume.