Evaluation of Bosniak category IIF complex renal cysts

Abstract

Purpose: To evaluate moderately complex renal cysts of Bosniak category IIF.

Materials and methods: The regional ethics committee approved the study. In the period 2003-2009, radiological CT reports of 8,402 CT examinations of the kidneys were analysed retrospectively by one radiologist. All complex cystic lesions in the kidney (n = 550 in the same number of patients) were reclassified according to the Bosniak classification by two radiologists in consensus. If a patient had more than one lesion, only the highest Bosniak category was recorded. All Bosniak IIF lesions with ≥2-year follow-up were included in the study.

Results: Thirty-two Bosniak IIF lesions were found. Five lesions (16 %) were upgraded during follow-up and the patients were offered surgery. Pathology of three lesions showed papillary carcinoma, clear cell renal carcinoma and chronic inflammation, respectively. Due to comorbidity the remaining two patients were followed with CT without intervention. Ten lesions (31 %) with follow-up periods >5 years had no further radiological changes and clinical follow-up was stopped.

Conclusion: The use of Bosniak category IIF is clinically applicable, resulting in an overall surgical nephron-sparing approach to complex renal cysts.

Teaching points: • The Bosniak classification is used to categorise complex renal cystic masses • BIIF cysts behave mostly as benign lesions • Radiological progression in complexity occurs in only 16 % of cases • BIIF category seems promising for clinical application, potentially avoiding unnecessary surgery.

Fig. 1

Flowchart

Fig. 2

Transversal baseline a corticomedullary phase CT image of a 61-year-old male with a moderately complex renal cystic lesion showing minimal thickening of the wall and septa without enhancement (arrow), interpreted as BIIF. Transversal b corticomedullary phase and c nephrographic phase CT images after 4-year follow-up: The lesion progressed in complexity with enlargement of the intrarenal component leading to up-classification to BIII. Pathological diagnosis was clear cell renal carcinoma, primarily located focally in the septum

Fig. 3

Transversal baseline a corticomedullary phase CT image of a 61-year-old male with a moderately complex renal cystic lesion showing minimal thickening and calcification of the wall without enhancement (arrow), interpreted as BIIF. After 2-year follow-up the lesion progressed in complexity with a more irregular wall and was up-classified to BIII. Transversal b corticomedullary phase and c nephrographic phase images showing slightly thickened, partially calcified wall without measurable contrast enhancement (arrowhead) after the lesion had been up-classified. Pathologic diagnosis was papillary renal cell carcinoma

Fig. 4

Corticomedullary phase CT images in a transversal plane and b coronal plane of a 68-year-old male with a moderately complex renal cystic lesion (arrow) showing hairline-thin smooth septa and wall with minimal thickening and calcification of septa without measurable contrast enhancement (arrowhead). There was no progression of the lesion after 5-year follow-up

Fig. 5

Transversal a non-contrast, b corticomedullary phase and c nephrographic phase CT image of a 66-year-old female with a moderately complex renal cystic lesion (arrow) showing few septa without measurable contrast enhancement (arrowhead), interpreted as BIIF. During the last 3-year follow-up, the lesion progressed in size but not in complexity. Note the small hemangioma in the liver

Fig 6

Transversal a non-contrast, b corticomedullary phase and c nephrographic phase CT image of a 70-year-old female with an indeterminate complex renal cystic mass (arrow) showing multiple septa with calcification and a suspicious nodular area without measurable contrast enhancement. The arrowheads show one example of such a suspicious area. The lesion was interpreted as BIIF but very close to a BIII and has been stable for the first 2 years of follow-up

Fig 7

Transversal a non-contrast, b corticomedullary phase and c coronal nephrographic phase CT image of a 69-year-old female with a moderately complex renal cystic mass (arrow) showing the wall and some septa containing thick and nodular calcification (arrowhead). The lesion was interpreted as BIIF; no progression was seen after 4 years of follow-up

Fig. 8

Baseline transversal a non-contrast, b corticomedullary phase and c nephrographic phase CT image of a 64-year-old female with an indeterminate complex renal cystic mass (arrow) showing multiple septa with calcification and some slightly thickened septa with perceived enhancement (arrowhead). The lesion was interpreted as BIIF and has been stable for the first 3 years with MRI follow-up (not shown)

Fig 9

Transversal a non-contrast, b corticomedullary phase and c nephrographic phase CT image of a 85-year-old male with a typical benign BII exofytic hyperdense cyst (arrow) measuring 35 HU in all phases

Fig 10

CT images of an 85-year-old male with a large renal cell tumour on the right side (not shown) and a left-sided indeterminate complex renal cyst with thickened enhancing wall, categorised as BIII. The patient underwent right-sided nephrectomy and percutaneous cryoablation on the left side. Transversal corticomedullary phase CT images of (a) baseline and (b) 3 month after right-sided nephrectomy. The BIII lesion (arrow) is almost solid after 3 months, indicating aggressive behaviour. No progression was seen at 6-month follow-up imaging after percutaneous cryoablation (c)