Potential pitfalls in the frozen section evaluation of parenchymal margins in nephron-sparing surgery

With advances in radiographic imaging, there has been an increase in the incidental detection of small renal cell carcinomas, with a resultant increase in partial nephrectomies for these tumors. Partial nephrectomy often necessitates assessment of renal parenchymal margins by frozen section. To determine the most common problematic "lesions" encountered on renal parenchymal margins, we evaluated all diagnostically challenging frozen sections that had been referred to a genitourinary pathologist. Frozen sections with detached atypical cells and crushed tubules were the most common lesions that presented diagnostic uncertainty. We found that normal constituents of renal parenchyma, namely tubules and glomeruli, can be mistaken for neoplasia. Neoplastic tubules of low-grade renal cell carcinomas may be misinterpreted as thickly cut, crushed benign tubules, and the significance of tubulopapillary "adenomas" in frozen sections is unclear. The present report highlights diagnostic difficulties that pathologists may encounter on frozen sections of renal parenchymal margins.