Longitudinal Multi-Modality MRI–Ultrasound Cyst-Level Analysis of Polycystic Kidney Disease in a Feline Model

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 reproducible 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 reproducible loss of visible boundaries between adjacent cysts without implying luminal communication. Serial US provided high-frequency temporal context and supported MRI-defined trends. 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 that the integration of volumetric MRI with serial ultrasound enables the identification of unilateral acceleration and cyst-level structural remodeling that may be overlooked by kidney-level volumetrics alone. Although limited to a single case, the standardized and open-source workflow establishes a reproducible framework with potential applicability to human autosomal dominant PKD imaging research.