Black thyroid adenoma - Clinical, histochemical, and ultrastructural features

A 22-year-old woman with a "hot" thyroid nodule who was being treated with minocycline for severe acne vulgaris is presented. A partial thyroidectomy specimen revealed a black adenoma. Microscopically, the black pigment was f ound in the follicular cells and the colloid of the adenoma. The pigment wa s bleached with potassium permanganate and was Fontana-Masson stain positiv e. It was negative for iron, periodic acid-Schiff, and acid-fast Ziehl-Neel sen stains. All these feature suggest a melanin-like pigment. However, elec tron microscopic examination revealed a dense osmophilic material present w ithin the lysosomes of the follicular cells. No melanosomes were present. T wenty-six previously reported cases are reviewed, and the possible mechanis ms for the deposition of the pigment in the adenoma and its relation to min ocycline degradation products are discussed.