Fine Needle Aspiration Using Improved Agar Microbiopsy is Highly Concordant With Renal Mass Final Diagnosis and Subclassification

Purpose: Computerized tomography and ultrasound are usually sufficient for preoperative evaluation of renal masses greater than 5 cm. For renal masses less than 5 cm additional histological evaluation could improve diagnosis and treatment decisions. We investigated the concordance between an improved agar microbiopsy technique and conventional cytology for diagnosing renal tumors. Materials and Methods: We performed fine needle aspiration in 40 renal masses after nephrectomy using a 22 gauge needle, obtaining multiple blind aspirations from the tumor surrounded by Gerota's fascia. Four conventional smears were prepared from each aspiration. An alcohol Carbowax™ solution was drawn up in the syringe and expelled in a vial. The fluid in the vial was processed according to our modified agar microbiopsy method using an additional cycle of centrifuging the hot sediment mixed in agar. Histological sections were prepared for light microscopy and immunohistochemistry. Cytology smears and agar microbiopsy sections were evaluated by 2 pathologists blinded to the definitive histological diagnosis. Results: The series consisted of 28 renal cell carcinomas, including 25 clear cell, 2 chromophobe and 1 papillary lesions, 7 urothelial cell carcinomas, 3 oncocytomas, 1 angiomyolipoma and 1 unclassified malignant tumor. Agar microbiopsy was concordant with the final histological diagnosis in 39 of 40 cases (correlation 0.98). Classic cytology was concordant with definitive histology in 21 of 40 cases (correlation 0.52). In 5 of 40 cases cytology identified malignancy but did not subtype the tumor correctly. Of the aspirates 15% contained too few diagnostic cells. Conclusions: Ex vivo fine needle aspiration using an improved agar microbiopsy block technique is highly concordant (98%) with the final diagnosis and subclassification of renal masses. Future validation using an in vivo pretreatment setting is needed to determine its clinical value.

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