Post-fine-needle aspiration spindle cell nodules of the thyroid (PSCNT).

Postoperative spindle cell proliferations have been well described in the lower genitourinary tract. These lesions show an exuberant proliferation of spindle cells with bland cytology and numerous mitoses. We report similar lesions in the thyroid gland of 10 patients who had undergone fine-needle aspiration (FNA). The proliferations were nodular, measured 1 to 7 mm, and were relatively circumscribed and nonencapsulated. In most cases, they were limited to the central part of the preexisting thyroid lesions and showed plump spindle cells with a rich network of thin-walled blood vessels and an inflammatory component constituted mainly of histiocytes and few lymphocytes. Mitotic figures were exceedingly rare. Immunostains showed diffuse positivity with smooth muscle actin, suggesting a myofibroblastic nature to the spindle cell component, and endothelial markers highlighted a network of thin-walled blood vessels. The histiocytic component stained with the macrophage marker CD68. The degree of cellularity was variable and may be related to the interval between FNA and surgery, size of the biopsy needle, and undetermined host response factors. We believe it is important to recognize these nodules as posttraumatic benign lesions without clinical consequence to avoid misdiagnosis of other lesions in thyroid-containing spindle cells, such as anaplastic carcinoma, medullary carcinoma, and sarcoma.