ESOU 2019: Diagnosis and Treatment of Cystic Renal Masses: Classification and Role of Cross-Sectional Imaging

Prague, Czech Republic ( Dr. Alessandro Volpe presented the classification and role of cross-sectional imaging in the treatment of cystic renal masses. Dr. Volpe notes that there are three kinds of renal masses: solid, cystic, and mixed; renal cell carcinomas (RCCs) are generally solid, but 5-7% are cystic.

Dr. Volpe highlighted the CT Bosniak classification of renal cysts, the aim of which is to classify renal cysts according to the risk of malignancy:

  • Bosniak I: these are simple, benign cysts with a 0-2% risk of malignancy. These cysts are hairline-thin walled, without septations, calcifications or solid components. They are the same density as water, with no enhancement with contrast. There is no need to follow these cysts.
  • Bosniak II: these are also benign cysts with a 0-5% chance of malignancy. These may contain a few hairline thin septa, fine calcifications in the cyst wall or septations, and are uniformly high-attenuated lesions <3 cm. These cysts have sharp margins without contrast enhancement and there is no need for follow-up imaging.
  • Bosniak IIF: these are low risk cysts with a 17-25% risk of malignancy and more hairline-thin septa than Bosniak II cysts. They have minimal enhancement, minimal thickening, and calcifications. There is no enhancing soft tissue and are totally intrarenal and well marginated non-enhancing high attenuation lesions ≥3 cm in size. These cysts are observed and followed expectantly.
  • Bosniak III: these are indeterminate cysts with a 30-54% risk of malignancy with thickened irregular walls or septa. These cysts do enhance and the recommendation is for surgical excision.
  • Bosniak IV: these are malignant cysts with 90-100% risk of malignancy. They have enhancing soft-tissue components and the recommendation is for surgical excision.
Dr. Volpe notes that MRI imaging is used for selected patients if CT is not possible or is inconclusive. MRI often has better resolution, contrast, and characterization of cystic lesions compared to other imaging modalities. When comparing CT vs MRI, CT provides information on (i) function and morphology of the contralateral kidney, (ii) primary tumor extension, (iii) venous involvement, (iv) assessment of lymph nodes, and (v) visualize the condition of the adrenal glands and liver. Furthermore, CT imaging is the tool of choice for characterizing renal masses. MRI may add information to the CT, such as (i) solid enhancing components in complex cystic masses, (ii) high resolution of cystic lesions (Bosniak IIF), (iii) assess fat content in low-fat AMLs, and (iv) locally advanced malignancy/venous involvement if poorly defined on CT scan.

The role of percutaneous biopsy for characterization of cystic renal masses has recently been addressed in a systematic review and meta-analysis1. Whereas the estimate for sensitivity of solid renal masses is 99.1%, it is only 83.6% for cystic renal masses. As such, the EAU guidelines state “core biopsies have low diagnostic yield for cystic renal masses and should not be recommended in these cases unless areas with a solid pattern are present (Bosniak IV cysts)”.

Dr. Volpe concluded with several take-home messages:

  • The Bosniak classification remains the standard for characterization of cystic masses
  • CT is the cross-sectional imaging of choice
  • MRI is indicated if CT is not possible or inconclusive
  • Percutaneous biopsy is not recommended

Presented by: Alessandro Volpe, MD, University of Eastern Piedmont Hospital, Maggiore Della Carita Hospital, Novara, Italy

Written by: Zachary Klaassen, MD, MSc – Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, Twitter: @zklaassen_md, at the 16th Meeting of the European Section of Oncological Urology, #ESOU19, January 18-20, 2019, Prague, Czech Republic

1. Marconi L, Debastani S, Lam TB, et al. Systematic review and Meta-analysis of Diagnostic Accuracy of Percutaneous Renal Tumour Biopsy. Eur Urol 2016 Apr;69(4):660-673.

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Diagnosis and Treatment of Cystic Renal Masses: Role of Contrast Enhanced Ultrasound