Fine‐needle aspiration cytology of metastatic spindle cell follicular thyroid carcinoma: A case report

Abstract

Follicular thyroid carcinoma, spindle cell variant is extremely rare. The tumor is predominantly composed of spindle cells with a fusiform appearance that are arranged in intersecting fascicles. Fine‐needle aspiration biopsy of this entity has not been previously described. We report a case of a 58‐year‐old woman who presented with metastasis to a left neck lymph node 15 years after the original diagnosis. Fine‐needle aspiration cytology showed numerous bland, spindled to epithelioid cells with thin, elongated, and plump nuclei with finely granular chromatin and inconspicuous nucleoli. The tumor cells had a moderate amount of cytoplasm with occasional elongated cytoplasmic tails. The cells were arranged in irregular aggregates with a fascicular pattern or singly dispersed. The tumor cells demonstrated positive staining for pan‐keratin, PAX8, thyroid transcription factor‐1, and thyroglobulin, which confirmed thyroid primary origin.