Aetiology of non-diagnostic renal fine-needle aspiration cytologies in a contemporary series

OBJECTIVES: To determine the aetiology of non-diagnostic renal fine-needle aspiration cytologies (FNACs) in a contemporary series. PATIENTS AND METHODS: We retrospectively reviewed our institutional database of renal FNACs performed between 1995 and 2005. There were 118 patients with renal lesions that underwent FNAC. Indications for FNAC were indeterminate complex renal cysts, significant medical comorbidities, previous history of malignancy, multiple bilateral renal lesions, and suspected metastatic disease. A cytotechnologist was present during the FNA procedure to perform Diff-Quik staining and ensure an adequate sample of cells were obtained. Except for seven (six open, one ultrasound-guided), all of the FNACs were performed with CT guidance. RESULTS: The median (range) number of passes for each FNAC session was 2.7 (1-6). Of the 16 FNACs performed for indeterminate complex renal cysts, nine (56%) were adequate with the cytodiagnosis of benign cysts. Of the seven inadequate specimens, three had benign cysts and another three were non-diagnostic due to acellularity. Therefore, the technical failure rate was 19% (3/16) for indeterminate complex renal cysts. The last patient had a cytodiagnosis of benign cyst and the final histological diagnosis of renal cell carcinoma (RCC; papilllary, grade III). Therefore, this represents a sampling error (false negative rate) of 0.8% (1/118). For the 102 solid renal masses, 22 (22%) had inadequate specimen by Diff-Quik staining. The technical failure rate (inability to obtain sufficient epithelial cells) was 16% (16). In 18 patients, immunocytochemistry (ICC) was used to differentiate primary renal parenchymal tumours from others such as transitional cell carcinoma (TCC), lymphoproliferative, colon, and lung. There were two FNACs with misdiagnosis (2%), where ICC was not used. In both, the cytodiagnosis was TCC and the final histological diagnosis was RCC in one and atypical urothelium in another. CONCLUSIONS: Non-diagnostic renal FNACs can be attributed to misdiagnosis (2%), sampling error (0.8%) and technical failure (16%).