# Defining new radiological patterns to improve classification of Bosniak III and IV cystic renal masses

## TL;DR

This study introduces new radiological patterns to better classify Bosniak III and IV cystic kidney masses, improving the distinction between benign and malignant cases.

## Contribution

The paper proposes four new radiological patterns for classifying Bosniak III and IV cystic renal masses, enhancing diagnostic accuracy compared to existing classifications.

## Key findings

- Twenty-four percent of Bosniak III-IV lesions were reclassified as solid tumors using the 2019 Bosniak criteria.
- Acute-angle nodules were a statistically significant indicator of malignancy.
- Proposed patterns (CRM-IP, CRM-CNP, CRM-PP, CRM-CCP) improved classification of benign and malignant lesions.

## Abstract

We aimed to compare Bosniak III and IV cystic renal masses (CRM) using Bosniak classification version 2005 (BC-v2005) versus BC-v2019 and analyze radiological findings and patterns of benignity and malignancy.

We retrospectively reviewed all Bosniak III-IV CRMs using BC-v2005 at our center with four-phase CT confirmed pathology, between January 2014 and June 2019. Two radiologists independently re-evaluated each lesion using both BCs, including findings of benignity and malignancy. Bosniak III-IV CRMs were classified in four radiological patterns: inflammatory (CRM-IP), cystic nephroma (CRM-CNP), papillary (CRM-PP), and clear cell (CRM-CCP). Characteristics of patterns were compared.

Out of 97 patients, 57 Bosniak III-IV CRMs met the inclusion criteria. Twenty-four (42.10%) lesions were reclassified as solid tumours using BC-v2019. Any lesion was downgraded to IIF or lower. Nine (15.78%) lesions were upgraded to Bosniak III-IV CRMs by BC-v2019, despite benign lesions. The presence of acute-angle nodules was the only statistically significant sign of malignancy (p < 0.01). All benign lesions, not considered solid, were included in the two patterns of benignity, characterized by thickened septa and/or wall and without acute-angle nodules. All malignant CRMs presented two patterns of malignancy, proposed as acute-angle nodules. All clear cell carcinomas presented with hyperenhancing acute-angle nodules in the arterial phase. Pattern classification was better for BC-v2005 and BC-v2029, differentiating benign and malignant CRM.

The proposed four radiological patterns improved performance than BC-v2019 in classifying benign lesions (CRM-IP and CRM-CNP) and malignant ones (CRM-PP and CRM-CCP), with wall and septa thickening and acute-angle nodules as relevant biomarkers.

The online version contains supplementary material available at 10.1007/s00261-025-05092-7.