Table 3 The Bosniak renal cyst classification system – adapted from reference [59]
Bosniak I  • Simple cyst  o Hairline-thin wall, no septations, no calcifications, no solid components  o Management: Nil  o Malignant potential: Approximately 0 % |  |
Bosniak II  • Minimally complex  o May contain a few hairline-thin septa with no perceivable enhancement, fine calcification or short segment of thicker calcification in wall or septa, or uniformly high-attenuation lesions on CT <3 cm that are sharply marginated and do not enhance  o Management: Nil  o Malignant potential: Approximately 0 % |  |
Bosniak IIF  • Minimally complex  o Multiple hairline-thin septa, perceived septal enhancement but no measureable enhancement, minimal wall thickening, calcification may be thicker and nodular, no enhancing soft tissue components, or totally intra-renal non-enhancing high-attenuating renal lesions >3 cm  o Management: Ultrasound or CT follow-up  o Malignant potential: Approximately 5 % |  |
Bosniak III  • Indeterminate  o Thickened irregular or smooth walls or septa with measureable enhancement  o Management: Partial nephrectomy or radiofrequency ablation  o Malignant potential: Approximately 55 % |  |
Bosniak IV  • Clearly malignant  o All criteria of Bosniak III but also contain discrete enhancing soft tissue components independent of the wall or septa  o Management: Partial or complete nephrectomy  o Malignant potential: Approximately 100 % |  |