Management of a 1.2 cm Simple Renal Cyst
No follow-up imaging or treatment is required for this asymptomatic 1.2 cm simple renal cyst on the left kidney inferior pole. 1
Rationale for No Intervention
Simple renal cysts are benign lesions that do not require surveillance or specific treatment in asymptomatic patients. 1 The imaging findings in this case demonstrate all characteristics of a simple cyst:
- Small size (1.2 x 1 x 1 cm)
- Well-defined margins
- No septations, wall thickening, or solid components
- Located in typical position (inferior pole)
Natural History Evidence
The majority (86%) of simple renal cysts increase in size over time, but this growth is not associated with development of complex features or malignant transformation. 1 In a longitudinal CT study following 222 simple renal cysts over 7.5 years, none developed septations or solid components despite 78% increasing by ≥6% in volume per year. 1
When Imaging Follow-Up Would Be Indicated
Follow-up imaging is only warranted if:
- The cyst develops complicated variations (new septations, wall thickening, solid components, or internal echoes), which would raise concern for malignancy 2
- Symptoms develop, including flank pain, hematuria, hypertension, or palpable mass 3
- The cyst becomes infected, presenting with fever and localized pain 4
Critical Distinction from Indeterminate Masses
This case differs fundamentally from an indeterminate renal mass. The ACR Appropriateness Criteria specify that homogeneous masses measuring <20 HU on unenhanced CT or 10-20 HU on contrast-enhanced CT are considered benign cysts requiring no further evaluation. 5 Your ultrasound findings are consistent with a simple cyst meeting these benign criteria.
Common Pitfall to Avoid
Do not confuse simple cyst growth with need for surveillance. 1 Providers and patients often become concerned when cysts enlarge on incidental imaging, but size increase alone without development of complex features does not warrant continued monitoring or intervention in asymptomatic patients. 1