Abstract

There is a lot of difficulty in the diagnosis of follicular lesions of the thyroid by fine needle aspiration cytology(FNAC). The main purpose of this report is offering more guidance regarding the cytologic appearance to distinguish follicular neoplasm from nodular goiter and laying stress on the presence of mixed group. The histologic and cytologic findings of 23 follicular neoplasms and 13 nodular (adenomatous) goiters were reviewed. Histologic specimens were classified into the microfollicular(MIF), mixed(MIX), and nodular goiter(NG) groups. The comparison of histologic patterns with histologic diagnosis revealed that all the lesions with predominantly microfollicular, trabecular, or solid pattern were follicular carcinoma and all the lesions with predominantly macrofollicular pattern were nodular goiter. The distinguishing cytologic features for the MIF group were irregular cell arrangement in cell groups(100%, p=0.00001), absence of atrophic follicular cells(100%, p=0.0007), abundant microfollicles(100%, p=0.002), pleomorphic nuclei(100%, p=0.002), not predominant syncytial smear pattern(100%, p=0.002), heterochromatin(100%, p=0.032), absence of macrofollicles(100%, p=0.038), scant colloid(100%, p=0.04), clear background(83%, p=0.00006), and uniform sized follicles(83%, p=0.014). And regular cell arrangement(honeycomb appearance) in cell groups(85%, p=0.0000), atrophic change of follicular cells(69%, p=0.0002), syncytial smear pattern(54%, p=0.006), monomorphic nuclei(85%, p=0.008), and hemorrhagic background(100%, p=0.027) were characteristic features of the NG group. Seventeen out of 36 cases(47%) were the MIX group composed of combined cytologic features of the MIF and NG groups. Therefore the frequent presence of the MIX group is considered to be main cause of the difficultyin the diagnosis of follicular lesions by FNAC. The mixed morphologic feature may support the hypothesis of a biologic "continuum" between nodular goiter and follicular neoplasm of thyroid gland.

• Keywords: Fine needle aspiration cytology;Follicular neoplasm;Nodular goiter;Thyroid;