Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment

We examined the relationship between tumor size and malignancy among solid renal tumors, and the relationship between tumor size and RCC subtype within tumors with renal cell carcinoma (RCC). We identified 2,770 adult patients who underwent radical nephrectomy or nephron sparing surgery for sporadic unilateral nonmetastatic solid renal tumors between 1970 and 2000. All pathology specimens were reviewed by a urological pathologist for diagnosis, and in RCC tumors, for histological subtype and nuclear grade. There were 376 benign (12.8%) and 2,559 (87.2%) malignant tumors. The percentage of benign tumors decreased from 46.3% for those less than 1 cm to 6.3% for those 7 cm or greater. Among RCC tumors the percentage that were clear cell increased from 25.6% for those less than 1 cm to 83.0% for tumors 7 cm or greater, while the percentage that were papillary decreased from 74.4% for those less than 1 cm to 10.0% for tumors 7 cm or greater. No RCC tumors less than 1 cm were chromophobe compared to 7.0% of tumors 7 cm or greater. The percentage of malignant tumors that were high grade RCC increased from 2.3% for those less than 1 cm to 57.7% for RCC tumors 7 cm or greater. Only 1% of all tumors less than 1 cm and 9.2% of all tumors less than 2 cm were high grade malignancies. As tumor size increased there was a significant increase in the odds of having a malignant compared to a benign tumor, clear cell compared to papillary RCC and high grade compared to low grade malignancy.

The radiologic diagnosis of renal cysts (and their differentiation from renal neoplasms) has come a long way since the 1950s when the approach was surgical exploration, unless clinically contraindicated, for every renal mass detected using urography. Nephrotomography, renal angiography, and cyst puncture have contributed over the ensuing years to the differentiation of cyst from tumor. However, for the most part, sonography and CT (or a combination of these when necessary) have become the main diagnostic techniques for evaluating renal masses, and with their use we have never been more accurate, noninvasive, and relatively economically efficient. The more widespread use of CT has enabled serendipitous discovery of many small renal carcinomas, the removal of which should result in an improvement in the overall cure rate of patients with renal parenchymal neoplasms. On the other hand, we are also discovering many more cysts than we have previously. We must be on guard, therefore, against discovering lesions for which we are unable to establish a radiologic diagnosis of benignity, because this will only increase the need for exploratory surgery once again. It is thus imperative that imaging studies be performed with great care, that diagnoses be based on rigid criteria, and that more experience with difficult lesions be gained so that the proper approach to treatment will be determined. If we are able to accomplish this, then the present radiologic age can be remembered as a time when great advances in the evaluation of renal masses were made, with resultant improved patient management and cure of disease.