What is the approach to managing renal cysts?

Management of Renal Cysts

The management of renal cysts should follow the Bosniak classification system, with simple cysts (Bosniak I and II) requiring no intervention or follow-up, Bosniak IIF cysts requiring surveillance, and Bosniak III/IV cysts often requiring intervention when oncologic benefits outweigh risks. 1, 2, 3

Classification and Risk Assessment

• Renal cysts should be classified using the Bosniak classification system which predicts malignancy risk: Bosniak I and II (simple cysts) have ~0% risk, Bosniak IIF ~10% risk, Bosniak III ~50% risk, and Bosniak IV ~100% risk of malignancy 1, 2, 4
• Simple renal cysts are characterized by well-defined margins, absence of internal echoes on ultrasound, and no contrast enhancement on CT or MRI 2, 3
• High-quality, multiphase, cross-sectional abdominal imaging is essential to optimally characterize renal cysts, including assessment of complexity, degree of contrast enhancement, and presence or absence of fat 1
• Ultrasonography is the preferred initial imaging modality for detecting and monitoring simple renal cysts due to its non-invasive nature, lack of radiation, and cost-effectiveness 3, 5

Management Algorithm Based on Cyst Type

Simple Renal Cysts (Bosniak I and II)

• No intervention is required for asymptomatic simple renal cysts 2, 4, 6
• No routine follow-up imaging is necessary for confirmed Bosniak I and II cysts 2, 7
• Symptomatic simple cysts may require intervention, with aspiration and sclerotherapy as first-line treatment 7
• Simple aspiration alone is ineffective and leads to cyst recurrence; aspiration should be accompanied with injection of a sclerosing agent 7

Bosniak IIF Cysts

• Active surveillance with repeat imaging in 6-12 months is recommended 2
• CT or MRI with and without contrast is preferred for follow-up imaging 2, 4
• Changes in cyst characteristics during surveillance (development of internal septations, wall thickening, solid components, calcifications, or irregular enhancement) warrant further investigation 4

Complex Cystic Masses (Bosniak III and IV)

• For Bosniak III cysts, cautious surveillance is a reasonable alternative to primary surgery, as surgery constitutes overtreatment in approximately 49% of cases 1
• For Bosniak III/IV cysts where oncologic benefits outweigh risks, intervention is recommended 1, 2
• Nephron-sparing approaches should be prioritized, especially in patients with solitary kidney, bilateral tumors, known familial RCC, or preexisting chronic kidney disease 1, 2, 3
• Active surveillance is an option for initial management of patients with small (<2 cm) Bosniak III/IV complex cystic renal masses 1, 2

Interventional Options

• Laparoscopic cyst decortication may be considered for symptomatic cysts that fail aspiration and sclerotherapy 8
• Partial nephrectomy should be prioritized for cT1a renal masses when intervention is indicated 1, 2
• The transperitoneal laparoscopic approach should only be used for simple renal cysts, while the retroperitoneal approach may be better for complicated renal cysts 8
• For confirmed malignant cysts, negative surgical margins should be a priority while preserving as much normal parenchyma as possible 1

Role of Renal Mass Biopsy

• Core biopsies are not recommended for cystic renal masses due to low diagnostic yield unless areas with a solid pattern are present (Bosniak IV cysts) 1, 3, 4
• Renal mass biopsy should be considered when a mass is suspected to be hematologic, metastatic, inflammatory, or infectious 1
• Never assume a nondiagnostic biopsy indicates benignity 3, 4

Follow-up Recommendations

• For patients with treated benign renal masses, occasional clinical evaluation and laboratory testing for sequelae of treatment is sufficient without routine periodic imaging 1, 2
• For patients with treated malignant renal masses, periodic medical history, physical examination, and laboratory testing should be performed 1
• A solitary cyst in childhood requires follow-up imaging as it may be a sign of ADPKD in children with a positive family history 3, 4

Special Considerations

• Changes in the characteristics of a simple renal cyst during surveillance warrant further investigation with CT or MRI due to increased risk of malignancy 4
• Consider referral to nephrology for patients with high risk of CKD progression, including those with eGFR less than 45 ml/min/1.73 m², confirmed proteinuria, or diabetics with preexisting CKD 1
• Treatment success for symptomatic cysts should be defined by symptom relief rather than volume reduction 4