Figure 3:

Distinguishing wall and septa irregularity from nodules by using the Bosniak classification of cystic renal masses, version 2019. Images show examples of convex protrusions within 30-mm Bosniak III and Bosniak IV cystic masses (measurements are to scale). Enhancing convex protrusions that arise from a wall or septa are either nodules (any size if they have acute margins with the walls or septa, or ≥ 4 mm if they have obtuse margins with the wall or septa [a feature of Bosniak IV]) or irregular thickening (≤3 mm if they have obtuse margins with wall or septa, a feature of Bosniak III). Size measurements are obtained perpendicular to the wall or septum of origin. If convex protrusion(s) are on both sides of a wall or septum, the cumulative perpendicular distance is used and excludes the thickness of the underlying wall or septum. Orange features have acute margins and blue features have obtuse margins. Bosniak III features are examples of focal irregular thickening. Bosniak IV features are examples of nodules.