What is the treatment and management for a cyst on the kidney?

Management of Kidney Cysts

The management of kidney cysts depends on their classification, with simple cysts (Bosniak I and II) typically requiring no treatment unless symptomatic, while complex cysts (Bosniak III and IV) may require surgical intervention due to their malignant potential. 1

Classification and Diagnosis

• Kidney cysts should be characterized using the Bosniak Classification of Cystic Renal Masses, which determines the likelihood of malignancy 1
• High-quality, multiphase, cross-sectional abdominal imaging (MRI, CT scan) is essential to properly characterize renal masses, including assessment of tumor complexity, degree of contrast enhancement, and presence or absence of fat 2
• For suspected renal malignancy, a comprehensive metabolic panel, complete blood count, and urinalysis should be obtained 2
• In patients with a solid or complex cystic renal mass, CKD stage should be assigned based on glomerular filtration rate (GFR) and degree of proteinuria 2

Management Based on Cyst Type

Simple Cysts (Bosniak I and II)

• Asymptomatic simple cysts (Bosniak I and II) require no further evaluation or follow-up 1
• When a solitary cyst is detected in childhood, follow-up imaging is recommended as this may be an early sign of polycystic kidney disease 2
• If simple cysts become symptomatic (pain, infection, hemorrhage, hypertension), treatment options include:
  • Percutaneous aspiration with sclerotherapy as first-line treatment 3
  • Surgical decortication for recurrent or very large symptomatic cysts 3
  • Laparoscopic approaches are highly effective with minimal morbidity 3

Complex Cysts (Bosniak III and IV)

• Complex cysts (Bosniak III and IV) have malignant potential and typically require surgical intervention 1
• For patients with a solid or Bosniak 3/4 complex cystic renal mass, a urologist should lead the counseling process and consider all management strategies 2
• Intervention is recommended when the anticipated oncologic benefits outweigh the risks of treatment and competing risks of death 2
• Options include:
  • Partial or total nephrectomy
  • Ablation therapy
  • Active surveillance in select cases 2

Special Considerations for Active Surveillance

• For patients with a solid or Bosniak 3/4 complex cystic renal mass where risk/benefit analysis is equivocal, renal mass biopsy should be considered for further risk stratification 2
• Follow-up imaging should be obtained approximately 3-6 months later to assess for interval growth 2
• Active surveillance with potential delayed intervention may be pursued if the patient understands and accepts the associated oncologic risks 2
• For small renal masses <2cm, the oncologic risk is very low, making active surveillance an acceptable option, especially in patients with limited life expectancy 2

Management of Cysts in Polycystic Kidney Disease

• In autosomal dominant polycystic kidney disease (ADPKD), management focuses on controlling blood pressure, managing pain, and preserving kidney function 2
• Renin-angiotensin system inhibitors (ACEi or ARB) are recommended as first-line treatment for hypertension in ADPKD patients 2
• For patients with ADPKD aged 18-49 years with CKD G1-G2 and BP >130/85 mm Hg, a target BP of ≤110/75 mm Hg is recommended 2
• Pain management may include analgesics, spinal-cord stimulation for refractory pain, and nephrectomy only in cases of severe intractable pain 2

Management of Cyst Complications

Cyst Infection

• For suspected kidney cyst infection, diagnostic features include serum C-reactive protein ≥50 mg/l or white blood cell count >11 × 10^9/l 2
• Blood cultures should be obtained if kidney cyst infection is suspected 4
• Treatment requires 4-6 weeks of antibiotic therapy, preferably with lipid-soluble antibiotics (e.g., trimethoprim-sulfamethoxazole, fluoroquinolone) for better cyst penetration 2

Polycystic Liver Disease

• Treatment options for symptomatic polycystic liver disease include aspiration sclerotherapy, transarterial embolization, laparoscopic cyst fenestration, combined partial hepatectomy, or liver transplantation in severe cases 2
• The choice of treatment depends on liver phenotype, with aspiration sclerotherapy suitable for one or few large dominant cysts, while diffuse disease may require more invasive approaches 2

Follow-up Recommendations

• Patients with treated malignant renal masses should undergo periodic medical history, physical examination, laboratory studies, and imaging to detect signs of metastatic spread or local recurrence 2
• Laboratory testing should include serum creatinine, estimated glomerular filtration rate, and urinalysis 2
• For patients with pathologically-proven benign renal masses, occasional clinical evaluation and laboratory testing are recommended, but routine periodic imaging is generally not required 2

Pitfalls and Caveats

• Simple fluid aspiration without sclerotherapy is ineffective and leads to cyst recurrence 5
• Prenatally-detected "simple" renal cysts may not actually be simple - over half may have modified diagnoses on follow-up, requiring serial imaging 6
• The distinction between Bosniak II and III cysts can be challenging due to interobserver variability, which may influence treatment decisions 7
• In patients with suspected kidney cyst infection, it's important to differentiate from cyst hemorrhage or kidney stones 2