Page 2 - CUA guideline on the management of cystic renal lesions

Managing cystic renal lesions

Evidence synthesis cohort. The authors demonstrated very good interobserver
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and intraobserver variation among uro-radiologists. Most of
the observed variation was seen among cysts categorized as
Bosniak classification – Introduction Bosniak II, IIF, and III. It is the panel’s opinion that when there
is disagreement or doubt regarding the classification of a renal
Renal cysts can be easily identified using standard med- cyst, such case should be presented at a multidisciplinary
ical imaging and, in most cases, a histological diagnosis meeting. (Level of evidence: 4; Recommendation: D)
is not required. However, lesions that are more complex
may require a more detailed characterization to allow for Description of Bosniak classification
determination of differential diagnoses and subsequent
management approach. By means of the Bosniak classification, renal cystic lesions
The Bosniak renal cyst classification was initially described can be categorized in increasing order according to risk of
4
in 1986 and was later updated to add a new category called malignancy as follows (Table 1):
category IIF. It was originally described using computed
5
tomography (CT) imaging, but other modalities, such as mag- Bosniak category I
netic resonance imaging (MRI), ultrasound (US), or contrast-
enhancement ultrasound (CEUS), are now being used to help Lesions classified as category I are simple renal cysts and rep-
better delineate these lesions. 6-10 The panel believes that if resent the majority of renal lesions detected by abdominal
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a complex cyst is first identified on US, contrast-enhanced imaging. These lesions are characterized by their regular con-
axial imaging should be performed to better characterize the tour and a clear interface with the renal parenchyma. They do
cyst. (Level of evidence: 4; Recommendation: D) not contain any septa, or calcifications, nor do they demonstrate
Although the Bosniak classification remains the most com- enhancement following intravenous contrast agent injection.
monly used classification to characterize renal cysts, it has They are homogeneous, with fluid attenuation varying from
traditionally been subject to poor interobserver agreement. 5, 0–20 HU on CT scan. These lesions are also easily identifiable
11-17 Nevertheless, a recent report by Graumann et al has valid- by US and appear as thin-walled, anechoic lesions with pos-
ated the reproducibility of the updated classification in a large terior enhancement and sharply marginated smooth walls. 5,8

Table 1. The Bosniak classification and management recommendations
Bosniak classification – key findings Recommendations
Bosniak category I (simple renal cyst)
• Usually round or oval shape • No followup required
• Anechoic with posterior enhancement on US
• Regular contour with clear interface with renal parenchyma
• No septa, calcification or enhancement
Bosniak category II
• Thin septum (<1 mm) • No followup required
• Fine calcification (often small, linear, parietal, or septal)
• Small hypderdense cyst (<3 cm; >20 HU)
• No perceived contrast enhancement
Bosniak category IIF
• Cyst unequivocally categorized as category II or III cysts • Followup recommended
• Multiple thin septa or a slightly thickened, but smooth septa • Imaging at 6 months and 12 months after diagnosis and then annually
• Calcifications – thick or nodular for at least 5 years if no progression.
• No perceived contrast enhancement
• Large hyperdense cysts (≥3 cm)
Bosniak category III
• Uniform wall thickening and/or nodularity • Surgical excision is suggested
• Irregular, thickened, and/or calcified septa • Conservative management and RFA in select cases
• Contrast-enhancing sept
Bosniak category IV
• Wall-thickening • Malignant until proven otherwise
• Gross, irregular, and nodular septal thickening • Surgical excision is suggested
• Solid contrast-enhancing component, independent of septa • Potential role for pretreatment RTB (of solid component) to confirm
malignancy
• RFA and conservative management in select cases
US: ultrasound; RFA: radiofrequency ablation; RTB: renal tumour biopsy.

CUAJ • March-April 2017 • Volume 11, Issues 3-4 E67