From the Guidelines
A renal cyst requiring further evaluation should be assessed with additional imaging studies, typically starting with a dedicated renal ultrasound if not already performed, and if concerning features are present, a contrast-enhanced CT scan or MRI should be obtained, as recommended by the European Association of Urology guidelines 1.
Evaluation of Renal Cysts
When evaluating a renal cyst, it is essential to consider the Bosniak classification system, which helps determine the risk of malignancy and guides management decisions. The Bosniak classification system categorizes cysts into five categories based on CT or MRI diagnostic criteria, with Bosniak I and II cysts generally being benign and requiring no follow-up, while Bosniak IIF cysts need periodic imaging surveillance every 6-12 months for 3-5 years.
Imaging Modalities
The choice of imaging modality depends on the specific characteristics of the cyst and the clinical context. Computed tomography (CT), ultrasound (US), and magnetic resonance imaging (MRI) are the imaging modalities used to detect and characterize renal masses (RMs) as solid or cystic 1. Contrast-enhanced US can be helpful in specific cases, and CT and MRI cannot reliably distinguish oncocytoma and fat-free angiomyolipoma from malignant renal neoplasms.
Management of Complex Cysts
Bosniak III and IV cysts have a higher risk of malignancy and typically warrant urological consultation for possible surgical intervention. Patients should be monitored for symptoms such as pain, hematuria, or signs of infection. Simple cysts (Bosniak I) are common, occurring in over 50% of people over age 50, and usually require no treatment unless symptomatic. Complex cysts need evaluation because approximately 40-60% of Bosniak III and 85-100% of Bosniak IV cysts represent renal cell carcinoma.
Additional Considerations
Patients with multiple or bilateral cysts should also be assessed for polycystic kidney disease, especially if there is family history. The American Urological Association (AUA) guidelines recommend that clinicians obtain high-quality, multiphase, cross-sectional abdominal imaging to optimally characterize and clinically stage the renal mass, and that patients with suspected renal malignancy should undergo comprehensive metabolic panel, complete blood count, and urinalysis, with metastatic evaluation including chest imaging to evaluate for possible thoracic metastases 1.
From the Research
Renal Cyst Evaluation
- A renal cyst is considered for further evaluation when it exhibits certain features such as calcification, high attenuation, septations, multiple locules, enhancement, wall thickening, or nodularity 2.
- The Bosniak classification is a valuable tool for clinicians to categorize renal cysts and determine the need for further evaluation or surgery 3.
- Computed tomography (CT) is the gold standard for evaluating renal cysts, but other imaging modalities such as ultrasound and magnetic resonance imaging (MRI) can also be useful 2, 3, 4.
Imaging Modalities
- Ultrasound can be useful for further evaluation of homogeneously hyperattenuating renal lesions detected on CT, with a sensitivity and specificity of 81.8% and 92.9%, respectively 4.
- CT can overestimate lesion distance to skin compared to ultrasound, which can affect the choice of biopsy method 4.
- MRI can provide additional information on the signal intensity of the cyst, which can help in differentiating between benign and malignant lesions 2.
Management
- Lesions that are multiloculated or demonstrate enhancement, wall thickening, or nodularity usually require surgery 2.
- When multiple features are present, the mass should be managed according to its most aggressive feature 2.
- Percutaneous biopsy of complex renal cysts can be well tolerated and accurate in the majority of cases, but the decision to biopsy should be made on a case-by-case basis, considering the risks and benefits 3.