Abstract
A 49-year-old female presented with a nontender mass in the neck. Fine-needle aspirate revealed spindle cells in a vaguely whorled pattern. The cells were fairly uniform and had elongated nuclei with fine chromatin. It was diagnosed as a cellular spindle cell neoplasm of uncertain histogenesis. Total thyroidectomy was performed revealing a well-circumscribed mass in the right lower pole extending substernally for 2 cm. The tumor was highly cellular and characterized by fascicles of spindle cells, focally displaying a biphasic pattern. The glandular component had a tubopapillary pattern. Occasional small mucous cysts were found adjacent to the tumor and in the opposite lobe, suggesting that the tumor might have arisen from the epithelial inclusions or remnants of branchial pouch within the thyroid. The spindle cells were immunoreactive for cytokeratin, epithelial membrane antigen, and vimentin and negative for thyroglobulin, calcitonin, chromogranin, desmin, myoglobin, and actin. Ultrastructurally, the spindle cells had abundant tonofilaments and well-developed desmosomes. These findings are consistent with a newly described entity, spindle epithelial tumor with thymus-like element (SETTLE), an intrathyroid lesion with a potential for delayed metastasis. Int J Surg Pathol 4(3):00-00, 1997
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