What is the appropriate management for a patient with a renal cyst?

Management of Renal Cysts

The management of renal cysts should be based on the Bosniak classification system, with simple renal cysts (Bosniak I and II) requiring no intervention or follow-up when asymptomatic, while complex cysts (Bosniak III and IV) typically warrant surgical intervention due to their higher malignancy risk. 1, 2

Classification and Diagnosis

• 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 1, 3
• Simple renal cysts are characterized by well-defined margins, absence of internal echoes on ultrasound, and no contrast enhancement on CT or MRI 1, 3
• High-quality, multiphase, cross-sectional abdominal imaging should be obtained to optimally characterize renal masses, including assessment of tumor complexity, degree of contrast enhancement, and presence or absence of fat 4
• 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
• MRI may be superior for characterizing renal lesions when iodinated contrast cannot be administered 4

Management Algorithm Based on Cyst Type

Simple Renal Cysts (Bosniak I and II)

• No intervention or follow-up is required for asymptomatic simple renal cysts regardless of size 1, 2, 5
• Treatment success is defined by symptom relief rather than volume reduction 1
• For symptomatic simple cysts, management options include:
  • Percutaneous aspiration with sclerotherapy as first-line treatment 6, 7
  • Laparoscopic cyst decortication for recurrent or very large symptomatic cysts 6
  • Retroperitoneal approach is generally preferred, especially in infected or hydatid renal cysts 6

Moderately Complex Cysts (Bosniak IIF)

• 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
• Changes in cyst characteristics during surveillance (development of internal septations, wall thickening, solid components, calcifications, or irregular enhancement) warrant further investigation 1, 2

Complex Cysts (Bosniak III and IV)

• Intervention is recommended when the anticipated oncologic benefits outweigh the risks 4, 2
• Nephron-sparing approaches should be prioritized, especially in patients with solitary kidney, bilateral tumors, or preexisting chronic kidney disease 2
• For cT1a tumors (<7 cm), partial nephrectomy is recommended when intervention is indicated 4
• Active surveillance is an option for initial management of small (<2 cm) complex cystic renal masses, with short-term cancer-specific survival rates exceeding 95% in well-selected patients 4, 2
• Thermal ablation may be considered as an alternative approach for the management of cT1a renal masses <3 cm in size 4

Special Considerations

• Symptomatic cysts may present with flank pain, hematuria, hypertension, or infection 6, 8
• Simple renal cysts may be associated with hypertension, particularly when multiple cysts are present 1
• A solitary cyst in childhood requires follow-up imaging as it may be a sign of autosomal dominant polycystic kidney disease (ADPKD) in children with a positive family history 1, 3
• Core biopsies are not recommended for cystic renal masses due to low diagnostic yield unless areas with a solid pattern are present 1, 2
• Never assume a nondiagnostic biopsy indicates benignity 1, 2

Treatment Outcomes

• Percutaneous aspiration and sclerotherapy with ethanol for simple renal cysts has shown complete resolution in 22% of cases and significant size reduction in most others 7
• Symptomatic relief occurs in approximately 75% of patients following ethanol sclerotherapy 7
• Laparoscopic decortication is highly efficacious and associated with high satisfaction rates with minimal morbidity for symptomatic cysts that fail aspiration and sclerotherapy 6