Diagnostic value of processing cytologic aspirates of renal tumors in agar cell (tissue) blocks

Objective: To adapt a method enabling utilization of most of the harvest from a fine needle aspirate in an effort to improve diagnostic accuracy in the assessment of a renal tumor in a single histologic slide. Study Design: In a series of 43 renal tumors, 2 fine needle aspirations were performed, 4 smears were prepared after each aspiration for conventional cytology and the remaining aspirate was processed for the improved agar microbiopsy (AM) method. Conventional cytology slides, AM slides and surgical specimens were diagnosed separately, after which the diagnoses were compared. Immunohistochemistry was performed as required on the AM sections. Surgical specimens served as the gold standard. Results: In 53% of conventional cytologic smears, the cellular yield was sufficient to render a correct diagnosis. In 12% the diagnosis was incorrect, in 21% only a differential diagnosis could be formulated, and in 14% too few diagnostic cells were present in the conventional smears for a cytologic diagnosis. It was, however, possible to correctly diagnose histologic sections from 97% of AM tissue blocks. In 11 cases this was facilitated with immunohistochemistry. In only 1 case did the AM tissue block contain too few cells to formulate a diagnosis; the conventional cytologic sample in this case contained enough diagnostic cells. In all cases the AM diagnosis was confirmed in the definitive surgical specimen. Conclusion: Our AM technique for processing fine needle aspirates from renal tumors results in a major enhancement of diagnostic accuracy of such aspirates and should be valuable in the preoperative diagnosis of large, as well as small, renal tumors.