Fine needle aspiration cytology, histology and MIB-1 proliferative index in a case of dyshormonogenetic goitre.

The fine needle aspiration (FNA) cytologic findings along with histology and MIB-1 proliferative index in a case of dyshormonogenetic goitre is presented. A 12-year old female child from non-endemic zone presented with a isotopically cold solitary thyroid nodule with a history of goitre being present since birth. Past history of any neck irradiation or maternal ingestion of any goitrogen during the antenatal period and family history of goitre were negative. FNA cytology revealed an extremely cellular preparation with predominantly microfollicular pattern without colloid. Nuclei were round to oval, slightly enlarged with evenly distributed chromatin and inconspicuous nucleoli. Larger tissue fragments also showed foci of solid cell groups with nuclear crowding, overlapping and loss of polarity in addition to the prevalent microfollicular pattern. Occasional tissue fragments showed solid groups of trapped follicular epithelial cells in the matrix of fibrocollagenous tissue. Histology showed an intensely hyperplastic follicular cells with nodule formation, irregular fibrosis, pseudo capsular or vascular wall invasion mimicking malignancy. Immunohistochemistry for calcitonin was negative but thyroglobulin was positive. MIB-1 (Ki-67) proliferation index varied from 0.05 to 0.26 (mean 0.13) in the hyperplastic nodules versus 0.9 to 2.1 (mean 1.34) in the hyperplastic solid microfoci scattered amidst the grossly normal appearing thyroid tissue. The possible cytologic diagnostic pitfalls in favor of follicular neoplasm is discussed.