Validation of the updated Bosniak classification (2019) in pathologically confirmed CT-categorised cysts
Number:28ESURABS0040
Type:Scientific Electronic Presentation
Authors: Magdalena Szewczyk-Bieda, Leo Morgan, James Lucocq, Ketan Rathod, Ghulam Nabi
Keywords:Bosniak classification, New Bosniak classification system 2019, renal cyst characterisation
SECTIONS
Objectives
·The Bosniak classification stratifies renal cysts using radiological appearances to predict the risk of malignancy and guide management.
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·Categorising cysts according to the original 2005 Bosniak classification has a number of shortcomings. It suffers from subjective criteria, significant interobserver variation and frequent inappropriate resection of benign cysts (1).
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·The updated Bosniak classification in 2019 sought to address this by revising the criteria, with the intent of categorising a higher proportion of cysts in lower risk groups and reduce benign cyst resections (2).
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·The aim of the present study was to compare the diagnostic accuracy and inter-observer agreement of the...

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Material and methods

 

·All patients with complex renal cysts diagnosed between January 2009 and December 2019, from a catchment 420,000 people in the east of Scotland, were recorded.
 
·Those without dual or triple-phase characterisation CT, and a resected/biopsied Bosniak cyst with histopathology, were excluded.
 
·The dual phase CT protocol was a non-contrast acquisition followed by a nephrographic phase (100 seconds). When triple phase was used an arterial (20-30 seconds) phase was included.
 
·Resected/biopsied cysts were categorised according to Bosniak classifications (v2005 and v2019) and the diagnostic accuracy was assessed with reference to histopathological analysis.
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Figure 1. Example of CT protocol for a Bosniak IV cyst (v2019). A – pre-contrast; B – arterial phase; C – nephrographic phase
Results
·61 complex renal cysts were included in the study, identified in 59 patients (median age 62 years; M:F = 1.3:1.0)
 
·The malignancy rate of the cohort was 83.6% (51/61).
 
·When using v2019, a higher proportion of malignant cysts were categorised as Bosniak ≥III (88.2% vs. 84.3%) and a significantly higher percentage were categorised as Bosniak IV (68.9% vs. 47.1%; p=0.049).

 

·v2019 upgraded a significant number of Bosniak IIF/III cysts (32.8%), due either enhancing wall or septal nodularity.

 

·In comparison to v2005, v2019 would have resulted in less benign cyst resections (13.5% vs. 15.7%).
 
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Figure 2. Categorisation of benign and malignant cysts, v2005 and v2019
Conclusions
·The present study demonstrates an improvement in the diagnostic accuracy of v2019 compared to v2005. A higher proportion of malignant cysts are categorised as Bosniak ≥III, and a significantly higher percentage were categorised as Bosniak IV.
 
·For v2019, enhancing nodules within cyst walls or septa were the primary reason for cyst upgrades from Bosniak IIF/III to IV.
 
·Using v2019, the rate of malignant cyst resection increases whilst the rate of benign cyst resection decreases.
 
·Interobserver agreement for v2019 was worse than v2005. This differs to other studies which have shown either no difference or that v2019 improves interobserver agreement (3). This may reflect the use of both...

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Figure 3. Pre-contrast (left) and nephrographic phase (right) images of a cyst upgraded from Bosniak III to IV by v2019. Note the enhancing nodular wall thickening medially

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