Abstract

We report a case of hyalinizing trabecular adenoma of the thyroid gland with its immunohistochemical and ultrastructural features. A 53 year-old euthyroid woman presented a well defined small cold nodule on a thyroid iodine scan. Microscopically, oval and elongated tumor cells were arranged in trabeculae, clusters and a "zellballen" pattern resembling paraganglioma with scattered follicles. Nuclear features were characterized by fine nuclear grooves, acidophilic intranuclear cytoplasmic inclusions and perinucleolar halos. Abundant extracellular eosinophilic fibrohyaline matrix resembling amyloid were also noted. Immunostaining of tumor cells was positive for thyroglobulin and negative for calcitonin. In addition, tumor cells displayed an unexpected, unique cytoplasmic immunoreactivity for MIB1. Electron microscopy revealed euchromatic nuclei with grooves, intranuclear cytoplasmic inclusions, intermediate filament stuffed cytoplasms and abundant extracellular basal lamina material.

• Keywords: Hyalinizing trabecular adenoma;Thyroid gland;Paraganglioma-like adenoma