The pursuit of understanding multinucleated giant cells in indeterminate and malignant thyroid cytology samples.

Background: Multinucleated giant cell (MGC) present in a variety of non-neoplastic and neoplastic lesions of the thyroid on cytology samples. We aimed to investigate whether certain MGC features that can help us in routine cytopathology practice.

Method: One hundred and thirty seven cases thyroid fine-needle aspiration material, which was diagnosed as indeterminate or malignant according to the Bethesda categorization, were reviewed. All cytomorphological features of the MGCs were documented. These features correlated with Bethesda categories and the final diagnosis of the subsequent surgical specimen.

Results: The presence of the MGCs was identified in 42% of the samples (58 cases-total 236 MGCs). Eighty eight of them (37%) had dense cytoplasm, 148 of them had foamy cytoplasm. The mean number of dense and foamy MGC per case was higher in the malignant category (3.2 for dense MGC and 6 for foamy MGC per case). All dense MGCs were found to be in patients with papillary thyroid carcinoma (PTC). Remarkably, follicular patterned lesions had less often dense MGC compared to papillary patterned lesions (16.6% and 46.8% respectively). We detected a nuclear irregularity in 49 dense MGC (55%), groove-like features in 24 dense MGC (27.2%), and presence of some material/cell in 8 dense MGC (9%).

Conclusion: The presence of dense MGC is an important finding for guiding accurate Bethesda categorization, especially in indeterminate and malignant categories. Besides, the presence of some material or cell in MGCs cytoplasm can be an important indicator for the prognosis of the PTC cases.