The ‘dark nucleus’ and disruptions of follicular architecture: possible new histological aids for the diagnosis of the follicular variant of papillary carcinoma of the thyroid

The ‘dark nucleus’ and disruptions of follicular architecture: possible new histological aids for the diagnosis of the follicular variant of papillary carcinoma of the thyroid Aims: In order to facilitate the diagnosis of malignancy in solitary thyroid nodules which are non-invasive low-grade tumours, i.e. follicular variant of papillary carcinoma (FVPC) for which few histological discriminators exist, a search was made for additional diagnostically useful histological features. Methods and results: Haematoxylin and eosin (H & E)-stained sections of 70 resection specimens of solitary thyroid nodules were re-evaluated by a panel of three pathologists, and their consensus and original diagnoses compared. In addition, H & E- and periodic acid–Schiff-stained sections were evaluated for various histological features and sections were stained by various immunohistochemical markers to evaluate their discriminative powers. The above features were also assessed in a group of 24 papillary carcinomas of the thyroid (PTCs) associated with regional metastases. The finding of ‘Orphan Annie eye’ nuclei was the best indicator of malignancy, and was closely related to the presence of nuclear grooves and cells with dense, dark nuclei. In addition, distorted follicular architectural features, i.e. ‘interconnecting cell masses’ and ‘fenestration’, were also significant indicators of malignancy. Tumours diagnosed as FVPCs had a significantly lower incidence of associated lymph node metastases than the classical PTCs. Conclusions: The use of optically clear nuclei as a diagnostic criterion when found only focally may not be sufficiently stringent in distinguishing FVPCs from follicular adenomas. When classical histological indicators of malignancy are equivocal, the diagnosis of FVPC may be facilitated by the above-mentioned features.