Atypical cytological presentation of granular cell tumour: Tumour-associated fibrosis may affect fine-needle aspiration cytology accuracy

The cytological features of granular cell tumour (GCT) are generally quite typical but, in some cases, the fine needle aspiration cytology (FNAC) diagnosis of GCT may be difficult or impossible because of unusual sites of onset or equivocal cytological features. In this report, two GCTs with atypical FNAC features are described in order to investigate the causes and provide possible diagnostic tips. From a series of nine histologically proven GCTs, two inconclusive FNAC cases were retrieved. Smears were poorly cellular showing isolated naked nuclei, anisonucleosis, granular chromatin and occasional small nucleoli. The background was finely granular in one case. Histological controls of these cases revealed marked fibrosis. Tumour-associated fibrosis in GCT is variable and does not seem to influence clinical behaviour but it influences the harvest and the integrity of granular cells collected by FNAC. When GCT smears are poorly cellular, attention should be paid to the granular background and to the few granular cells, if any, as they might be the only features to suggest a GCT.