What is the recommended screening and management approach for a patient with a Bosniak (Bosniak classification system) 2F renal cyst?

From the Guidelines

For a patient with a Bosniak 2F renal cyst, the recommended approach is active surveillance with follow-up imaging, as the malignancy risk is significant, with rates ranging from 10.9% to 38% in different studies 1. The management of Bosniak 2F renal cysts is crucial due to their potential for malignancy.

• The Bosniak classification system is used to determine the likelihood of malignancy in cystic renal masses, with Bosniak 2F lesions having a higher risk due to their complex features.
• According to a retrospective study of 156 Bosniak IIF lesions, 10.9% of the lesions progressed to malignancy between 6 months and 3.2 years 1.
• Another study of 312 prospectively classified Bosniak lesions found a malignancy rate of 38% for Bosniak IIF lesions 1.
• The recommended surveillance approach includes initial contrast-enhanced CT or MRI at 6 months, followed by annual imaging for 5 years.
• If the cyst remains stable in size and complexity during this period, surveillance can be discontinued, but if it demonstrates growth or increasing complexity, it should be upgraded to a higher Bosniak category and managed accordingly, potentially requiring surgical intervention.
• The goal of surveillance is to balance the risk of malignancy with the risk of unnecessary surgical intervention, allowing for early detection and treatment of potentially malignant lesions while avoiding overtreatment of benign lesions.
• The use of contrast-enhanced CT or MRI is essential for evaluating these lesions, as it helps to identify enhancing nodules, walls, or thick septa within the cystic mass, which are key to determining the probability of malignancy using the Bosniak classification 1.

From the Research

Bosniak 2F Screening Approach

The recommended screening and management approach for a patient with a Bosniak 2F renal cyst involves regular follow-up imaging to monitor for potential progression to malignancy.

• The majority of Bosniak 2F lesions remain benign, but a minor part may progress to malignancy 2, 3.
• Contrast-Enhanced Ultrasound (CEUS) is a promising diagnostic imaging modality for the follow-up of complex renal cystic lesions, offering higher spatial and temporal resolutions than CT or MRI, as well as an excellent safety profile and low financial costs 2.
• CT-guided biopsy can be used to differentiate malignancies and benign lesions needing intervention from benign complex cysts in Bosniak 2F and 3 renal cysts, with a sensitivity of 0.71 for malignancies, 0.87 for benign lesions needing intervention, and 0.91 for benign complex cysts 4.

Imaging Features and Follow-Up

Imaging features such as septa number, septa/wall thickness, and protrusions can be assessed using both CT and MRI, with increased septa number and more protrusions identified on MRI 5.

• The Bosniak Classification version 2019 (Bosniak.v2019) has improved specificity compared to the original Bosniak Classification, with maintained sensitivity and higher overall accuracy 5.
• Regular follow-up imaging is essential, as progression to malignancy can occur within 6 months to 3.2 years 3, and the majority of small Bosniak category 2F lesions remain stable or regress during active surveillance 6.

Management Considerations

Management considerations for Bosniak 2F renal cysts include:

• Active surveillance with regular follow-up imaging to monitor for potential progression to malignancy 6.
• CT-guided biopsy to differentiate malignancies and benign lesions needing intervention from benign complex cysts 4.
• Consideration of the patient's overall health and preferences when determining the best course of management.
• The use of CEUS as a diagnostic imaging modality for follow-up, due to its excellent safety profile, easy accessibility, and low financial costs 2.