Abstract
Background: Hyalinizing trabecular adenoma (HTA) is a rare benign thyroid tumor that is easily confused with papillary and medullary carcinoma.
Case: We experienced a case of HTA of the thyroid gland coexisting with a papillary carcinoma. A 53-year-old female complaining of a neck nodule had two strumae. The left struma was 1.5cm in diameter, and the right one was 2.0 cm in diameter. Aspiration biopsy cytology was performed for both strumae. Since nuclear grooves and pseudoinclusions were identified in both tumors, we diagnosed both tumors as papillary carcinoma. Microscopically, the left tumor was a well differentiated papillary carcinoma, but the right one was encapsulated and tumor cells were arranged in a trabecular pattern with hyalinized stroma. The cytoplasma of the right tumor cells was eosinophilic. Most nuclei were round or oval, and both nuclear grooves and pseudoinclusions were frequent. PAS reaction of the hyalinized stroma was positive, and cytoplasmic immunoreactivity for thyroglobulin was observed, but CEA and Calcitonin were both negative, so the right tumor was diagnosed as HTA. MIB-1 immunostaining of the cytoplasm and cell membrane of the right tumor was positive, and provided a useful finding in this case of HTA.
Conclusion: It may be difficult to differentiate HTA from papillary carcinoma cytologically in the same thyroid gland.
