Role Of Biopsy In Complex Cystic Renal Masses

The recommended treatment for complex cystic masses is either observation or surgery, which traditionally has meant nephrectomy, partial nephrectomy, enuclea-tion, or, more recently, laparoscopic surgery. Increasingly, radiofrequency ablation and cryosurgery are becoming options in patients who are not standard operative candidates. In the United States, unequivocal imaging diagnosis of renal malignancy is usually followed by surgical intervention without other confirmation. Biopsy is rarely performed, being reserved for selected cases where the patient has a known primary nonrenal tumor or lymphoma and biopsy is necessary to direct appropriate therapy.

One recent paper, however, advocates the biopsy of Category III cystic renal masses to avoid unnecessary surgery in the cases that prove to be benign. Harisinghani et al. described the results of CT-guided biopsies of 28 Bosniak Category III lesions (34). Fine needle aspirations and core biopsies were obtained of the suspicious areas of the cyst wall, septa, or calcification in multiple passes. Seventeen (61%) of the lesions were malignant and 11 (39%) were benign. The benign cases were followed up for periods of one to two years (median 18 months).

This study was subject to criticism, however, for misclassification of at least some lesions and inadequate period of follow-up in the benign group to assure stability (35). The authors' claim of a negative predictive value of biopsy of 100% has not been achieved by other investigators. In another study that included 16 cystic renal masses, Rybicki et al. showed percutaneous biopsy was only 33% sensitive with a negative predictive value of 87% (36). The authors do not advocate biopsy in these cases because of these results. Pathologists agree that the sensitivity of percutaneous biopsy in diagnosing cystic renal cell carcinoma is very low, rendering a negative result highly unreliable, a fact that should be communicated to the clinician (37). To be confident that a tumor will not manifest aggressive behavior, pathologic analysis of the entire lesion is mandatory (3). Another criticism of biopsy of cystic lesions is that less tissue is obtained, and it is well known that sampling errors can occur due to tumor cellular heterogeneity even in core solid tumor specimens. A false negative rate of 20% and a false positive rate of 34% were reported by Goethuys et al. in intraoperatively obtained renal mass core biopsies (38).

In addition to continued uncertainty, any biopsy may sufficiently alter a lesion's imaging characteristics to make follow-up for stability (which may be required in the case of a negative biopsy result) more confusing. Finally, complications of renal biopsy, such as pneumothorax, bleeding, pseudoaneurysm, infection, and tumor spill, are rare, but cannot be disregarded (35,36). Given the low sensitivity of biopsy for cystic renal cell carcinoma and the lingering problem of false negatives, Category III cystic renal masses appropriately classified with proper CT technique should be evaluated surgically (35-37).

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