Postoperative spindle cell nodule after thyroidectomy: a case mimicking recurrence with anaplastic transformation of thyroid cancer.

Background: Here, we report a case of a postoperative spindle cell nodule that mimicked recurrence with anaplastic transformation after thyroidectomy.

Methods: The course of the disease is described. The mass was studied morphologically and immunohistochemically.

Results: A 31-year-old woman underwent total thyroidectomy for papillary thyroid carcinoma. A mass suspected of recurrence was found 14 months later and caused dysphagia and dyspnea. An (18)F-fluorodeoxyglucose positron emission tomographic ((18)F-FDG-PET) scan showed a lesion with high uptake; however, a fine-needle aspiration biopsy (FNAB) was inconsistent with recurrent cancer. The mass was resected and was composed of elongated spindle cells, with eosinophilic cytoplasm within a myxoid background. Immunohistochemical staining was strongly positive for vimentin, focally positive for smooth muscle actin, desmin, and p53, and negative for cytokeratin AE1/AE3, Cam5.2, epithelial membrane antigen (EMA), and anaplastic lymphoma kinase (ALK-1).

Conclusion: Although postoperative spindle cell nodules are rare after thyroid surgery, it should be considered in the differential diagnosis for recurrent masses at the operative site.