Active surveillance of small renal masses

Most renal masses incidentally detected by cross-sectional images are benign, being mainly cysts, and if they are malignant, they are indolent in nature with limited metastatic potential. Enhanced renal masses less than 4 cm in size are known as small renal masses (SRMs), and their growth rate (GR) and the possibility of developing metastasis are extremely low. Delayed intervention of SRMs by closed and routine imaging follow-up known as active surveillance (AS) is now an option according to urological guidelines. Radiologists have a key position in AS management of SRMs even unifocal and multifocal (sporadic or associated with genetic syndromes) and also in the follow-up of complex renal cysts by Bosniak cyst classification system. Radiologists play a key role in the AS of both unifocal and multifocal (sporadic or associated with genetic syndromes) SRMs as well as in the follow-up of complex renal cysts using the Bosniak cyst classification system. Indeed, radiologists must determine which patients with SRMs or complex renal cysts can be included in AS, establish the follow-up radiological test algorithm to be used in different scenarios, perform measurements in follow-up tests, and decide when AS should be discontinued. The purpose of this article is to review the indications and management of AS in SRMs, especially focused on specific scenarios, such as complex renal cysts and multifocal renal tumors (sporadic or hereditary). In this work, the authors aimed to provide a thorough review of imaging in the context of active surveillance of renal masses.