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.
Hyalinizing trabecular adenoma is an uncommon benign thyroid tumor that is recently described in the literature. This tumor is easily confused with medullary carcinoma on surgical specimens and with papillay carcinoma on cytologic specimens. Herein we report the cytologic characteristics of a case of histologically proven hyalinizing trabecular adenoma of the thyroid gland. Cytologically, the aspirate showed trabecular or individually dispersed polygonal cells with finely stippled chromatin pattern, nuclear grooves, and eosinophilic nuclear pseudoinclusions. No colloid materials were noted in the background.
Hyalinizing trabecular adenoma of the thyroid gland is a rare benign neoplasm predominantly diagnosed in middle-aged women. Carney et al. first described this entity that may mimic paraganglioma, medullary carcinoma and papillary carcinoma in 1987. We describe cytologic and histopathologic features of a case of hyalinizing trabecular adenoma combined with occult papillary carcinoma in the opposite lobe. A 55-year-old woman presented with nontender palpable mass of the right neck for 6 months. The aspirate was cellular and contained small clusters and sheets of epithelial cells with abundant filamentous, vacuolated, and ill-defined cytoplasm. The nuclei were slightly pleomorphic and showed nuclear overlapping, nuclear grooves, and intranuclear cytoplasmic inclusions. Histologic examination showed hyalinizing trabecular adenoma in the right lobe and occult papillary carcinoma in the left lobe.