Histological and fine needle aspiration cytological features of Hashimoto thyroditis‐associated ‘angiomatoid’ papillary thyroid carcinoma

A SFT of the thyroid affects adults and presents as a slow-growing mass composed of fibroblast-like spindle cells; cytological smears show predominantly discohesive slender spindle-shaped cells and fragments of collagenized stromal tissue, as described previously. Similarly an inflammatory pseudotumour of the thyroid gland may be considered in the differential diagnosis although this is a rare lesion demonstrating fibrohistiocytic and myofibroblastic proliferation: the lesion is positive for vimentin and muscle-specific actin but negative for cytokeratin. We believe that the most important factor for making a correct diagnosis of SETTLE is awareness of this entity. This diagnosis must be considered in young patients who present with a swelling in the neck in the region of the thyroid and who do not fit into the usual thyroid tumours on cytomorphology. Immunocytochemistry is very useful in excluding other spindle cell predominant entities especially a medullary carcinoma, a synovial sarcoma and a solitary fibrous tumour, which are the major differential diagnoses of SETTLE.