The cytological diagnosis of paediatric renal tumours.

Fine needle aspiration cytology (FNAC) is used for preoperative diagnosis of paediatric renal tumours, especially in centres where preoperative chemotherapy is advocated in Wilms' tumour. This review focuses on salient cytological features in specific paediatric renal tumours, the approach to resolving a differential diagnosis and the role of ancillary methods in diagnosis of paediatric renal tumours. Crucial differential diagnoses include distinguishing: Wilms' tumour from benign tumours in the kidney like multicystic nephroma or congenital mesoblastic nephroma; aggressive non-Wilms' tumours of kidney like rhabdoid tumour of kidney; and Wilms' tumour from other paediatric round cell sarcomas like neuroblastoma, non-Hodgkin lymphoma etc. An approach based on classifying smears according to their cellular patterns as triphasic, round cell, spindle cell or epithelioid cell type assists in classifying paediatric renal tumours on cytology. Immunocytochemistry for WT1, cytokeratin, synaptophysin, leucocyte common antigen and MIC2 will aid in evaluating round cell tumours in the renal region, while WT1, bcl2, vimentin and desmin will be useful for spindle cell tumours in that region. Extra material can also be evaluated for demonstration of specific cytogenetic abnormalities in these tumours. A checklist of common tumours in a particular age group, relevant clinical information, awareness of distinctive and overlapping cytological features, and appropriate use of immunocytochemistry with cytogenetics go a long way in ensuring an accurate cytological diagnosis. Used judiciously, FNAC is as effective a tool as a core biopsy for preoperative diagnosis of paediatric renal tumours, and with experience a 92% accuracy rate can be achieved.