Intranuclear cytoplasmic inclusions and nuclear grooves in fine needle aspiration smears of papillary thyroid carcinoma and its variants: advantage of the count under an oil-immersion objective over a high-power objective.

OBJECTIVE

To determine the advantage of examining fine needle aspiration (FNA) smears of papillary thyroid carcinoma (PTC) under a 100 x oil-immersion objective, which is capable of optically sectioning the cells.

STUDY DESIGN

Two hundred neoplastic cells were counted under a high-power (40x) objective as well as oil-immersion (100x) objective in 54 PTC cases classified into variants: 14 follicular neoplasms, 8 Hürthle cell neoplasms, 5 medullary thyroid carcinomas and 9 hyperplastic lesions. The counts of cells with 2 important diagnostic features of PTC, intranuclear cytoplasmic inclusions (INCIs) and grooved nuclei, were compared between various groups and between high-power and oil-immersion objectives in each group.

RESULTS

Cytomorphologic features, such as INCI and nuclear grooves, were visible usually under 2 or 3 focal planes under the oil-immersion objective as opposed to a single plane under the high-power objective. In PTC cases, the mean cell count, 10.1 (+/- 1.75 SE) with INCIs, under the oil-immersion objective was significantly higher than the count, 6.1 (+/- 1.32 SE), under the high-power objective (p = 0.023). INCIs were not observed under the high-power objectives in 11 (20.4%) PTC cases, but in 5 (45.5%) of these they were visible under the oil-immersion objective. In PTC the mean cell count, 88.0 (+/- 4.96 SE), with grooved nuclei under the oil-immersion objective was also significantly higher than the count, 69.5 (+/- 4.87 SE), under the high-power objective (p = 0.010). Under the high-power objective, < 20.0% of cells with grooved nuclei were observed in 12 (22.2%) cases of PTC. However, examination under the oil-immersion objective revealed > or = 20.0% cells with grooved nuclei in 9 (75%) of these. In PTC the mean cell counts with INCIs as well as grooved nuclei under the oil-immersion objective were significantly higher than those of follicular neoplasms, Hürthle cell neoplasms, medullary carcinoma and hyperplastic lesions.

CONCLUSION

In PTC, examination of FNA smears for INCIs and grooved nuclei under an oil-immersion objective was diagnostically more useful as compared to a high-power objective.