Fine-needle aspiration of cystic lesions of the kidney - Morphologic spectrum and diagnostic problems in 41 cases

Although imaging studies show the nature of most cystic lesions of the kidn ey (RCs), many RCs require fine-needle aspiration (FNA)for accurate diagnos is. interpretation of the FNAs remains challenging. The FNA specimens of 41 RCs were reviewed and correlated with imaging studies. Final diagnoses for 30 cytologically benign lesions were simple cyst (28), acquired cystic kid ney (1), and cystic renal carcinoma (1). The fluid from the benign cysts di splayed macrophages, epithelial cells from the cyst lining, tubular cells, neutrophils, and Liesegang rings. Fluid from the acquired cystic kidney and the cystic renal cell carcinoma showed features similar to those of the be nign cysts. The 9 cases with "suspicious" cytology included 5 complex cysti c lesions displaying rare but atypical epithelial cell clusters, 3 low-grad e renal cell carcinomas with many mildly atypical papillary clusters of epi thelial cells, and 1 simple benign cyst with many tubular cells. The 2 cyto logically malignant lesions were cystic renal cell carcinomas with abundant tumor cells with partially clear cytoplasm and atypical nuclei admired wit h abundant macrophages and lymphocytes; I case developed in a kidney with a cquired cystic disease. Simple cysts remain the most frequently aspirated R Cs, but complex cystic lesions are increasingly recognized. Since many RCs are composed of independent loculi, a nonrepresentative sample is a potenti al problem, and cytologic-radiologic correlation becomes mandatory. The "su spicious" patterns identified in this study should serve as diagnostic guid elines and set the foundation for future validation.