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 thyroi d nodules which are non-invasive low-grade tumours. i.e. follicular variant of papillary carcinoma (FVPC') for which Few histological discriminators e xist, a search was made for additional diagnostically useful histological f eatures. Methods and results: Haematoxylin and eosin (H & E)-stained sections of 70 resection specimens of solitary thyroid nodules were re-evaluated by a pane l of three pathologists, and their consensus and original diagnoses compare d, In addition. H &- E- and periodic acid-Schiff-stained sections were eval uated for various histological features and sections were stained by variou s 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 'Orp han Annie eye' nuclei was the best indicator of malignancy, and was closely related to the presence of nuclear grooves and cells with dense, dark nucl ei. In addition. distorted follicular architectural Features, i.e. 'interco nnecting cell masses' and 'fenestration', were also significant indicators of malignancy. Tumours diagnosed as FVPCs had a significantly lower inciden ce of associated lymph node metastases than the classical PTCs, Conclusions: The use of optically clear nuclei as a diagnostic criterion wh en found only focally may not be sufficiently stringent in distinguishing F VPCs from follicular adenomas. When classical histological indicators of ma lignancy are equivocal, the diagnosis of FVPC may be facilitated by the abo ve-mentioned features.