Introduction:

To re-evaluate the former Bosniak classification (BC) version 2005 (v2005) of Bosniak III and IV cystic renal masses (CRM) using the new BC version 2019 (v2019) by computed tomography (CT) correlated with contrast-enhanced ultrasound (CEUS) and pathological findings to develop a better classification and avoid unnecessary surgeries.

Methods:

This retrospective unicentric review of Bosniak III and IV CRM according to BC-v2005 with pathological verification between January 2014 and June 2019, compared the classification of CRM by BC-v2005 with the BC-v2019 criteria by CT, correlated with CEUS and pathological findings.

Results:

Of 57 CRMs included, 51% previously considered as CRM with BC-v2005 were reclassified as solid by BC-v2019 and CEUS analysis. No benign CRM considered Bosniak III by v2005 was downgraded with v2019, while 9 previous Bosniak III v2005 benign CRM were upgraded to Bosniak IV. Four different patterns were found, two for benign CRM presenting with irregular septa and/or walls and no nodules (inflammatory and cystic nephroma patterns) and two for malignant CRM showing convex acute angle margin nodules (papillary and clear cell patterns).

Conclusion:

The classification of CRM by BC-v2019 was upgraded and solid, with no downgrading compared to BC-v2005. The use of four different patterns to differentiate CRM: those with enhancing irregular septa and/or irregular walls and no nodules (inflammatory and cystic nephroma patterns) versus those with enhancing nodules with acute angles (papillary and renal cell patterns); allows better treatment selection (active surveillance or surgery according to a benign or malignant classification), thereby avoiding unnecessary surgical intervention.

Funding: N/A