Lately, we did fine-needle aspiration on a right thyroid mass of a 47-year-old woman, which showed microfollicular neoplasm with numerous intranuclear inclusions on the cell block hematoxylin and eosin (H&E) slides (Fig. 1). The simultaneous fine-needle aspiration biopsy specimen air-dried Diff-Quick-smeared slides and alcohol-fixed Papanicolaou-stained smeared slides showed microfollicular lesion without the evidence of intranuclear inclusions. To exclude the possibility of follicular variant of papillary carcinoma, the thyroid mass was excised. The surgical excision H&E slides (Fig. 2) showed complete absence of intranuclear inclusions after scrupulous examination.
Unanimously recognized by most of the pathologists, the cytological features of thyroid papillary carcinoma include intranuclear inclusions, 1 nuclear grooves, 2 enlarged and oval nuclei, Orphan Annie-eyed optically clear nuclei, 3 powdery chromatin, 2 dense and metaplastic cytoplasm, high cellularity, papillary clusters without vessels, 1 viscoid colloid, multinuclear giant cells, psammoma bodies, 1 etc. Intranuclear inclusions are one key criterion for the diagnosis of thyroid papillary carcinoma in fine-needle aspiration biopsy. Many pathologists never forget to search for well-defined intranuclear inclusions for definite diagnosis of thyroid papillary carcinoma, but the sensitivity ranges from 54.17 to 100%. According to literature reports, intranuclear inclusions can be seen in fine-needle aspiration biopsy specimens of non-neoplastic thyroid lesions, i.e., Hashimoto's thyroiditis, or benign thyroid tumors, i.e., follicular adenoma, or other thyroid malignancies, i.e., medullary carcinoma or follicular carcinoma.
In our case, the discovery of intranuclear inclusions in the cell block could be a pitfall for pathologists in training. But the finding was questionable because of