A case of black thyroid associated with hyalinizing trabecular tumor

Black thyroid is an uncommon phenomenon of black pigmentation of thyroid parenchyma induced by chronic minocycline therapy. Thyroid tumors associated with black pigmented thyroid are rare. We describe here a 42-year-old woman with a black thyroid associated with hyalinizing trabecular tumor (HTT). The patient presented with a palpable left-sided thyroid nodule. She had taken minocycline for aphthous stomatitis and an oral ulcer for 9 years. The findings of fine needle aspiration biopsy and BRAF mutation analysis suggested a papillary carcinoma. The patient underwent a near-total thyroidectomy with central compartment node dissection. The surgical specimen showed a diffuse black thyroid and a 2-cm non-pigmented, well-circumscribed nodule in the left thyroid. Histopathologically, numerous black pigmented follicular epithelial cells and colloid were seen throughout the thyroid parenchyma, and the nodule was composed of elongated, polygonal cells in trabecular arrangement and dense hyaline stromas. The tumor cells showed a strong positive cytoplasmic reaction to Ki 67. All of these findings suggested a HTT, or a hyalinizing trabecular variant of papillary carcinoma, arising in a black thyroid. To our knowledge, this is the first case of black thyroid associated with HTT.