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Discordance between fine-needle aspiration cytology and histopathology in patients with mucoepidermoid carcinoma of parotid gland.

INTRODUCTION
Fine-needle aspiration cytology (FNAC) is an important diagnostic tool used preoperatively for the diagnosis of parotid lump. Mucoepidermoid carcinoma comprises 5-10% of all salivary gland tumours. It poses a diagnostic challenge on FNAC with high false negative rate. The objective of this study was to evaluate the discordance between cytology/FNAC and histopathology in patients with mucoepidermoid carcinoma.


MATERIAL AND METHODS
A cross-sectional study was conducted from 1 January 2010 to 31 December 2014. Patients aged 18 years and above with FNAC or histopathology suggestive of mucoepidermoid carcinoma were identified. FNAC when compared with histology (gold standard) was classified into true positive (presence of mucoepidermoid carcinoma correctly diagnosed on FNAC), true negative (absence of mucoepidermoid carcinoma correctly diagnosed on FNAC), false positive (FNAC incorrectly diagnosed mucoepidermoid carcinoma), false negative (FNAC failed to diagnose mucoepidermoid carcinoma).


RESULTS
A total of 16 patients fulfilled our eligibility criteria. Seven cytological samples were true positive (ie correctly diagnosed mucoepidermoid carcinoma by FNAC), eight cytological specimens were false negative (ie could not pick up mucoepidermoid carcinoma on FNAC). One case was false positive on cytology (ie diagnosed mucoepidermoid carcinoma on FNAC but was reported to be Warthin's tumour on histopathology) and none were true negative.


CONCLUSION
FNAC is not reliable for diagnosis of mucoepidermoid carcinoma. More than 50% of our patients had discordant results between cytology and histology. We recommend a high index of suspicion for mucoepidermoid carcinoma given the poor yield of cytology.