Nyquist sampling theorem and Bosniak classification, version 2019: effect of thin axial sections on categorization and agreement

Objective To determine if CT axial images reconstructed at current standard of care (SOC; 2.5–3 mm) or thin (≤ 1 mm) sections affect categorization and inter-rater agreement of cystic renal masses assessed with Bosniak classification, version 2019. Methods In this retrospective single-center study, 3 abdominal radiologists reviewed 131 consecutive cystic renal masses from 100 patients performed with CT renal mass protocol from 2015 to 2021. Images were reviewed in two sessions: first with SOC and then the addition of thin sections. Individual and overall categorizations are reported, latter of which is based on majority opinion with 3-way discrepancies resolved by a fourth reader. Major categorization changes were defined as differences between classes I–II, IIF, or III–IV. Results Thin sections led to a statistically significant major category change with class II for all readers individually ( p = 0.004–0.041; McNemar test), upgrading 10–17% of class II masses, most commonly to class IIF followed by III. Modal reason for upgrades was due to identification of additional septa followed by larger measurement of enhancing features. Masses categorized as class I, III, or IV on SOC sections were unaffected, as were identification of protrusions. Inter-rater agreements using weighted Cohen’s kappa were 0.679 for SOC and 0.691 for thin sections (both substantial). Conclusion Thin axial sections upgraded up to one in six class II masses to IIF or III through identification of additional septa or larger feature. Other classes, including III–IV, were unaffected. Inter-rater agreements were substantial regardless of section thickness. Key Points • Thin axial sections (≤ 1 mm) compared to standard of care sections (2.5–3 mm) led to identification of additional septa but did not affect identification of protrusions . • Thin axial sections (≤ 1 mm) compared to standard of care sections (2.5–3 mm) can upgrade a small proportion of cystic renal masses from class II to IIF or III when applying Bosniak classification, version 2019 . • Inter-rater agreements were substantial regardless of section thickness .