Does a 67‑year‑old woman with a 0.9 cm simple renal cyst in the left kidney require any follow‑up imaging or clinical surveillance?

Management of Small Simple Renal Cysts in a 67-Year-Old Woman

A 67-year-old woman with a 0.9 cm simple renal cyst requires no follow-up imaging or clinical surveillance of any kind. 1

Rationale for No Follow-Up

• Simple renal cysts are extremely common benign lesions that arise from the renal parenchyma and are not associated with malignant transformation when they meet strict criteria for a simple cyst (thin smooth wall, no septations, no solid components, anechoic fluid content). 1, 2

• The size of this cyst (0.9 cm) is well below any threshold that would warrant concern. Even cysts up to 10 cm in diameter that maintain simple characteristics do not require routine surveillance. 3, 2

• Asymptomatic simple renal cysts require neither treatment nor follow-up, regardless of size, as long as they maintain their simple morphology. 2

Natural History of Simple Renal Cysts

• While 86% of simple renal cysts increase in size over time (mean growth rate of 0.1 cm/year), this growth is not associated with the development of complex features such as septations or solid components. 1

• In a longitudinal study following 222 simple renal cysts over a mean of 7.5 years, none developed malignant characteristics despite the majority increasing in size. 1

• Enlargement of asymptomatic simple renal cysts does not indicate the need for follow-up imaging. 1

When Follow-Up Would Be Indicated

• Follow-up imaging is only mandatory if the cyst shape becomes irregular or develops complex features (septations, wall thickening, solid components, or enhancement on contrast imaging). 2

• Symptomatic cysts (causing pain, hematuria, hypertension, or infection) require intervention, but this patient's incidental finding does not fall into this category. 2, 4

Critical Distinction: Renal vs. Ovarian Cysts

It is important to note that the O-RADS classification system referenced in some of the provided evidence 3, 5, 6 applies exclusively to ovarian-adnexal lesions, not renal cysts. The management algorithms for ovarian cysts differ substantially from renal cysts and should not be applied to this patient's kidney finding.

Practical Recommendation

Document the finding as a benign simple renal cyst in the medical record and reassure the patient that no follow-up is needed. 2 If future imaging is performed for unrelated reasons and the cyst develops complex features (which is exceedingly rare), then re-evaluation would be appropriate at that time. 7, 2