Mr Will Finch MBBS BSc(Hons) MRCSUrology SpREdith Cavell Hospital

When to….Discharge, survey or operate

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 1 No septae Group 2 1-4 septae Group 3 5-9 septae Group 4 >9 septae

Thickness of wall and/or septae Group 1 Wall only Group 2 Hairline thin Group 2F Minimally thickened Group 3 Grossly thickened (>1mm)

and irregular

Israel et al. Radiology 2004;231:365-71

Bosniak Cat. n. malignancies/ n. in group

Ref I II III IV

[5] 0/22 1/8 5/11 26/29

[15] - 0/4 4/7 5/5

[16] ½ 1/7 4/13 7/10

[17] 0/7 4/5 4/4 6/6

[18] 0/15 29/49 18/18

[19] - 3/28 8/29 -

[20] - - 28/179* -

[21] - - 17/28 -

[23] 0/11 1 /2 10/10 12/12

Total 1/57 10/54 109/330 74/80

% CANCER 1.7 18.5 33.0 92.5

Warren et al. BJUI 2005;95:939-42

37 patients

Stage II 6 pts No cancers Stage IIF 10 pts 2 cancers (20%) Stage III 14 pts 4 cancer (30%) Stage IV 7 pts 6 cancer (86%)

Stage I&II No Follow up required Stage IIF Indeterminate risk requires

FU Stage III&IV Surgical management

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 IIF 81 pts Stage III 31 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 I No FU

Stage II No FU

Stage IIF Scan @ 6/12 and 1yrIf no evidence of

progression – discharge?

Or Scan @ 6/12, 1yr and 2yrs

and then discharge?

Stage III/IV Surgical 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?