Predictive value of fine-needle aspiration of the thyroid in the classification of follicular lesions.

BACKGROUND

Fine-needle aspiration has been less valuable in the diagnosis of follicular lesions than for other neoplasms of the thyroid. It has been observed that follicular carcinoma is found in microfollicular, but not macrofollicular lesions, and this has served as a guide to management for many surgeons. The authors attempted to determine what cytologic parameters might usefully distinguish these types of follicular lesion.

METHODS

The histologic findings and cytology of 56 thyroid lobectomies for follicular lesions that had adequate preoperative fine-needle aspiration of the thyroid (FNAT) were reviewed. Histologic specimens were classified into macrofollicular, mixed, and microfollicular groups. Cytologic features examined included the presence of colloid, irregularity of cell arrangements within groups, the presence and size of flat and folded cell sheets, three-dimensional clusters, and microfollicles and macrofollicles.

RESULTS

Of the histologic specimens, 15 were preponderantly (> 70%) microfollicular, 19 were mixed, and 22 were predominantly (> 70%) macrofollicular. Three cytologic features were useful in their distinction: none of the predominantly microfollicular but 24% of the mixed and predominantly macrofollicular had abundant colloid (P = 0.048). Likewise, none of the predominantly microfollicular but 27% of the mixed and predominantly macrofollicular had large follicles (P = 0.026). Finally, 73% of the predominantly microfollicular but only 37% of the mixed and predominantly macrofollicular showed irregularity or crowding of cells in groups (P = 0.018).

CONCLUSIONS

Used in combination, abundant colloid, regular spacing, and large follicles are helpful in distinguishing macrofollicular and mixed lesions from microfollicular ones, which have a higher malignant potential.