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

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.