Until now, the use of acetic and lactic acid for the treatment of thyroid nodular lesions, as well as histopathologic changes in the thyroid tissue after their intrathyroidal injections has not been described. The aim of this study is to evaluate macro- and microscopic changes in rat normal thyroid tissue induced by single intrathyroidal injection of acetic acid (AA) and lactic acid (LA) in different concentrations, as well as the influence of intrathyroidal acid injection on function of the recurrent laryngeal nerves. Male Wistar rats were divided into two groups of 50 (Group A and B). Rats of each group were divided into the subgroups of five. In each subgroup of Group A and B, AA and LA water solutions of different concentrations (0%, 2.5%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 80%), respectively, were injected into the right thyroid lobe. From Group A and B, 7 and 8 rats died, respectively (after injections of 50-80% AA and LA solutions). After 4 weeks post AA or LA injection the thyroid along with the surrounding tissues was excised and assessed macro- and microscopically in all rats that survived. Before the injection and just before the second operation, the vocal cord function was evaluated. Our results show that both, acetic and lactic acid of different concentrations damage rat normal thyroid tissue after a single intrathyroidal injection. The minimal concentrations of acetic and lactic acid that cause lethal changes in rat normal thyroid tissue are 20% and 10%, respectively. Acetic and lactic acid in the concentrations of 40% and 50%, respectively, and higher can cause injury of the tissues adjacent to the thyroid.

        Key words: acetic acid - lactic acid - thyroid nodule - percutaneous injection