What is the recommended follow-up imaging schedule for simple renal cysts?

From the Guidelines

Simple renal cysts that meet all criteria for being benign on initial imaging, such as those classified as Bosniak I, typically do not require routine follow-up imaging unless the patient develops symptoms. The Bosniak classification, updated in 2019, is a useful tool for predicting the risk of malignancy in renal cystic masses, with Bosniak I cysts having approximately 0% malignancy risk 1. For cysts with minimal complexity but considered likely benign (Bosniak category II), a single follow-up imaging study at 6-12 months may be performed to ensure stability.

Some key points to consider in the follow-up of simple renal cysts include:

• The extremely low malignancy risk of simple cysts, which is less than 1% 1
• The importance of avoiding unnecessary radiation exposure, healthcare costs, and patient anxiety
• The need to identify rare cases where a seemingly simple cyst may evolve to show more complex features over time
• The use of follow-up imaging to monitor for any changes in size or characteristics of the cyst, with a typical follow-up schedule of 6 months initially, then annually for 3-5 years for cysts with more concerning features (Bosniak category IIF)

It is essential to weigh the benefits of follow-up imaging against the potential risks and costs, and to individualize the follow-up approach based on the specific characteristics of the cyst and the patient's overall health status. For simple renal cysts with classic benign features, no further imaging is generally recommended unless the patient develops symptoms, as supported by the European Association of Urology guidelines on renal cell carcinoma 1.

From the Research

Follow-up Imaging Schedule for Simple Renal Cysts

• The recommended follow-up imaging schedule for simple renal cysts is not strictly defined, but studies suggest that most simple renal cysts increase in size over time without developing complex features 2.
• A study found that 86% of simple renal cysts increased in size over time, with 78% increasing by ≥6% in volume per year, but none developed septations or solid components on follow-up examinations 2.
• For asymptomatic simple renal cysts, no follow-up imaging is indicated 2.
• The Bosniak classification is widely used to categorize cystic renal lesions, but it is based on computed tomography (CT) findings, and ultrasonography (US) is often used for long-term follow-up due to its noninvasiveness and low cost 3, 4.
• For simple renal cysts that become symptomatic or complicated, non-conservative management options such as sclerotherapy, laparoscopy, and percutaneous endoscopic ablation may be considered 5.

Imaging Modalities for Simple Renal Cysts

• Ultrasonography (US) and computed tomography (CT) are commonly used imaging modalities for diagnosing and evaluating simple renal cysts 3, 4.
• CT is often used for initial evaluation, while US is used for long-term follow-up due to its noninvasiveness and low cost 3.
• Magnetic resonance imaging (MRI) may also be used in some cases, especially for lesions that are difficult to classify or remain indeterminate after CT 4.

Factors Affecting Follow-up Imaging

• The natural history of the cyst, presence of symptoms and/or complications, and patient choice are factors that affect the treatment decision and follow-up imaging schedule for simple renal cysts 5.
• The size and growth rate of the cyst, as well as the patient's overall health and medical history, may also influence the follow-up imaging schedule 2, 6.