Abstract

The presence of neuroendocrine cells is putative in thyroid hyalinizing trabecular tumor (HTT), although this entity requires a differential diagnosis from paraganglioma or medullary carcinoma of the thyroid, due to similarity of the growth pattern of the cells. Here, we present a case of HTT with a mixture of endocrine cells stained positive for somatostatin, chromogranin A and Grimelius' silver impregnation. The histology and results of other immunostainings were consistent with the features typical for HTT. In the world literature to date, only two cases of HTT with endocrine cells, including the current case, have been reported. Nevertheless, the cases may indicate the diversified differentiation of cells in HTT and may, in part, account for the resemblance of HTT to paraganglioma and medullary carcinoma.

Spindle cell metaplasia in thyroid adenoma or carcinoma is rare and its pathological features are not well characterized. Distinction of this entity from medullary or anaplastic carcinoma has an important clinical implication. We encountered a case of thyroid follicular adenoma associated with spindle cell metaplasia. It showed "tumor in tumor appearance" and neoplastic spindle cells were positive for thyroglobulin, thyroid transcription factor-1, vimentin and focally chromogranin A and somatostatin (SS). MIB-1 index was <1%. Ultrastructure of the spindle cells was reminiscent of follicular cell origin. From the findings from our case, spindle cell metaplasia appears to be a benign clinical entity, suggestive of multidirectional differentiation of follicular cells.