The cytomorphologic spectrum of Wilms tumour on fine needle aspiration: a single institutional experience of 110 cases.

OBJECTIVE

To analyse the cytomorphologic spectrum of Wilms tumour (WT) on aspirates, the largest series reported to date.

STUDY DESIGN

Adequate aspirates from paediatric renal tumours over a period of 17 years were reviewed and selected if subsequent excision showed WT or aspirates were diagnostic for WT and clinical/radiological evidence consistent with that diagnosis. Smears were re-examined for the proportion of components, degree of pleomorphism and mitosis.

RESULTS

Of 110 aspirates, smears were triphasic in 44 (40.0%), biphasic (blastema and tubules) in 36 (32.7%) and monophasic (blastema alone) in 30 (27.3%). Stromal predominance was seen in 11 aspirates (10.0%) and five showed rhabdomyoblastic differentiation; all 11 were triphasic. Mean mitotic rate was 9.3/5000 cells (range 4-39/5000). Nuclear atypia not amounting to anaplasia and without atypical mitoses was seen in 15 (13.6%); these presented diagnostic problems. Two aspirates (1.8%) were considered anaplastic (unfavourable), both having atypical mitoses. Criteria similar to histology (i.e. 3-fold or more variation in nuclear size, marked hyperchromasia with bizarre nuclei and atypical mitoses in a biphasic or triphasic aspirate) helped in distinguishing anaplastic WT. Histopathological correlation in 67 cases showed good correlation of blastemal predominance, stromal predominance and anaplastic histology with the corresponding cytology. However, 9/27 (33.3%) triphasic tumours had only blastemal cells on corresponding aspiration because of sampling error. Cytokeratin was positive in 4 of 20 aspirates with blastema alone.

CONCLUSIONS

Aspirates from WT were triphasic or biphasic in the majority (72.7%), permitting cytological diagnosis, which was improved by cytokeratin immunocytochemistry. Blastemal and stromal predominance on histology correlated well with cytology, but many triphasic tumours showed only blastema on aspiration. Anaplastic WT can be detected on aspirates using criteria similar to histology.