Insular carcinoma of the thyroid: report of a case with intact insulae and microfollicular structures

A case of insular carcinoma of the thyroid is presented, in which a prominence of microfollicular structures resulted in difficulty in distinguishing it from a follicular neoplasm of the thyroid. The patient presented with a single discrete thyroid nodule, aspiration of which yielded markedly cellular smears containing cells lying singly, in tight clusters and microfollicles. Criteria for separation of insular carcinoma of the thyroid from follicular neoplasms include the presence of intact insulae, high cellularity, and the presence of small amounts of necrotic debris.