Marginal vacuoles in fine-needle aspirates of follicular thyroid carcinoma

Marginal vacuoles (MV) found in Giemsa-stained fine-needle aspirates of the thyroid gland have been observed in toxic and also in non-toxic goiters. The aim of our retrospective study was to disclose the incidence and diagnostic significance of MV in 46 smears from 43 patients with primary and/or metastatic follicular thyroid carcinoma (FTC). Typical MV, MV-like structures, or both were found in 14 of 36 specimens (39%) of the primary tumor and in four of seven specimens (57%) obtained from metastases of FTC. No association between the appearance of MV/MV-like structures and degree of tumor differentiation was demonstrated. On the other hand, MV or/and MV-like structures were more frequently (69%) documented in hyperthyroid patients (P < 0.05). Accordingly, our study demonstrated relatively frequent appearance of MV or MV-like structures in FTC independent of tumor differentiation. Their appearance, however, seems to be associated with hyperthyroidism.