Active Surveillance for Small Renal Mass: Indications, Imaging, and When to Intervene

Summary Active surveillance (AS) is a nephron-sparing strategy for small renal masses (SRMs, ≤4 cm) that balances the indolent natural history of most SRMs against the morbidity of intervention. This review consolidates SRM definition, epidemiology, and growth kinetics; outlines patient/tumor selection criteria and progression triggers; details diagnostic evaluation and structured follow-up protocols; and presents outcomes, challenges, and controversies. Finally, we discuss emerging molecular, radiomic, and artificial-intelligence tools to refine AS and conclude with a forward-looking perspective on precision surveillance.