Longitudinal Multi-Modality MRI–Ultrasound Cyst-Level Analysis of Polycystic Kidney Disease in a Feline Model: A Proof-of-Concept Study

Abstract Polycystic kidney disease (PKD) in Persian cats is commonly monitored using total kidney volume (TKV); however, this kidney-level metric does not capture heterogeneity in individual cyst dynamics. Here, a standardized longitudinal imaging framework integrating volumetric magnetic resonance imaging (MRI) with serial ultrasound (US) is presented, enabling cyst-level analysis in a feline PKD model followed over two years. MRI-based volumetry quantified individual cyst growth rates and identified structural coalescence events, defined as the persistent loss of visible boundaries between adjacent cysts without implying luminal communication. Serial US provided high-frequency temporal context and supported MRI-defined trends, rather than replacing MRI-based structural assessment. The analysis revealed marked asymmetric progression, with significant enlargement and coalescence of right-sided cysts, while left-sided cysts remained stable. This dual-modality approach demonstrates the feasibility of integrating volumetric MRI with serial ultrasound for longitudinal cyst-level analysis, enabling the identification of asymmetric progression and cyst-level structural remodeling that may be overlooked by kidney-level volumetrics alone. Although based on a single case, this study demonstrates the feasibility of a standardized MRI–ultrasound workflow and provides a methodological framework for future validation in larger cohorts.