Category I. simple benign cysts showing homogeneity, water content, and a sharp interface with adjacent renal parenchyma, with no wall thickening, calcification, or enhancement. Category II. cystic lesions with one or two thin (≤ 1 mm thick) septations or thin, fine calcification in their walls or septa (wall thickening > 1 mm advances the lesion into surgical category III) and hyperdense benign cysts with all the features of category I cysts except for homogeneously high attenuation. A benign category II lesion must be 3 cm or less in diameter, have one quarter of its wall extending outside the kidney so the wall can be assessed, and be nonenhancing after contrast material is administered. Category IIF minimally complicated cysts that need follow-up. This is a group not well defined by Bosniak but consists of lesions that do not neatly fall into category II. These lesions have some suspicious features that deserve follow-up up to detect any change in character. Category III. true indeterminate cystic masses that need surgical evaluation, although many prove to be benign. They may show uniform wall thickening, nodularity, thick or irregular peripheral calcification, or a multilocular nature with multiple enhancing septa. Hyperdense lesions that do not fulfill category II criteria are including in this group. Category IV. nonuniform or enhancing thick wall, enhancing or large nodules in the wall, or clearly solid components in the cystic lesion. Enhancement was considered present when lesion components increased by at least 10 H.
Number of septae Group 1No septae Group 21-4 septae Group 35-9 septae Group 4>9 septae Thickness of wall and/or septae Group 1Wall only Group 2Hairline thin Group 2FMinimally thickened Group 3Grossly thickened (>1mm) and irregular Israel et al. Radiology 2004;231:365-71
Bosniak Cat. n. malignancies/ n. in group RefIIIIIIIV 0/221/85/1126/29 -0/44/75/5 ½1/74/137/10 0/74/54/46/6 0/1529/4918/18 -3/288/29- --28/179*- --17/28- 0/111 /210/1012/12 Total1/5710/54109/33074/80 % CANCER1.718.533.092.5 Warren et al. BJUI 2005;95:939-42
41 patients with Stage IIF Nearly 6yrs FU 36 masses remained unchanged on CT 3 masses got smaller These were considered benign 2 lesions increased in size and were removed, both were RCC’s Israel G, Bosniak Ml. Am J Roentgenol 2003;181:627-3
Does Stage IIF improve accuracy of Bosniak classification? O’Malley et al. J Urol 2009;182(3):1095 112 pts Stage IIF81 pts Stage III31 pts Median FU of 15 months 14.8% of Bosniak IIF lesions progressed in complexity (median of 11 months) No differences in tumour or patient characteristics for cysts that progressed and those that remained stable 33 patients with Stage III cysts had surgery Malignancy rate 81.8% Suggests increased accuracy of classification by low rate of progression (14.8%) for Bosniak IIF, and very high rate of malignancy in Stage III group (81.8%)
Stage INo FU Stage IINo FU Stage IIFScan @ 6/12 and 1yr If no evidence of progression – discharge? Or Scan @ 6/12, 1yr and 2yrs and then discharge? Stage III/IVSurgical exploration
No good quality studies to answer question of FU Subjective assessment on USS, less so on CT It appears that if Stage IIF diagnosed accurately Low risk of progression ~ 15% - 20% Progression occurs on average around 1yr Would be sensible that accurate rpt imaging reflects this Classification based on CT, but role for MRI or CEUS Individual patients choice re balance of risk and FU or exploration?