Cytomorphology and morphometry of small round-cell tumors in the region of the kidney

Small round-cell tumors (SRCTs), with malignant cell components measuring 10 m or less in diameter with scanty cytoplasm in alcohol-fixed smears, pose a diagnostic challenge at fine-needle aspiration cytology (FNAC), especially when they are situated in and around the kidney and need facilities such as electron microscopy, immunohistochemistry, tissue culture, and cytogenetics for their subtyping. A precise cytodiagnosis of SRCTs is important because a definite diagnosis is mandatory in preoperative diagnostic workup for presurgical chemotherapy in these cases. With this view in mind, an attempt has been made to diagnose SRCTs in the region of the kidney based on cytomorphology and morphometry alone so as to facilitate its diagnosis in a simple cytology laboratory of a developing country where facilities for auxiliary techniques are not easily available. Of 2,028 abdominal aspirates in a 12-yr period, 36 SRCTs were diagnosed in the region of the kidney by correlating with histology, radiology, and clinical features. The smears were studied for cellularity, morphology, pattern of cell arrangement, and smear background and morphometrically analyzed using an ocular micrometer. An aspirate with preponderant malignant round cells that were larger or double the size of red blood cells in air-dried smears or measured less than 10 micro in diameter in alcohol-fixed smears was considered as a small blue-cell tumor. Twenty-one were diagnosed as Wilms' tumor (WT), 10 were diagnosed as neuroblastoma (NB), 3 were ganglioneuroblastoma (GNB), 1 was a cellular congenital mesoblastic nephroma (CMN), and 1 was an adrenocortical carcinoma (ACC). Cell clusters with neuropil and cytoplasmic processes were diagnostic of NB, ganglion cells of GNB, and blastema with tubular differentiation in WT. Aspirates from CMN and ACC were considered as simulators/mimickers of SRCT because they had superficial resemblance to SRCT and their differentiating cytomorphological features observed at histology were too subtle to be noted at cytology. The latter were appreciated only on retrospective analysis after histological confirmation.Thus, morphometry in correlation with cytology, clinical history, physical findings, and radiological data is helpful in guided FNA for a definite diagnosis of SRCT in the region of the kidney. One needs to keep in mind the mimickers of small round-cell lesions at this anatomic site.