Thyroid cryotherapy in an experimental rat model.

In recent years cryotherapy has been more and more frequently used for the treatment of tumors of different organs. Until now, the use of cryotherapy for the treatment of thyroid lesions, as well as histopathologic changes in thyroid tissue after cryotherapy, has not been described. Nitrous oxide cryotherapy of one thyroid lobe in twenty 12-week male Wistar rats was performed. After 2 and 4 weeks, the cryotreated thyroid lobe and the second lobe along with a part of the trachea, esophagus, and the subhyoid muscles adhering to the thyroid were excised and assessed macro- and microscopically. The macroscopic evaluation, performed 2 and 4 weeks postcryotherapy, revealed atrophy of the cryotreated lobe in 4 and 3 rats, respectively, and reduction of the cryotreated lobe dimensions in 6 and 7 rats, respectively. In the specimens of the lobes excised 2 weeks following cryotherapy, examined microscopically, necrosis, granulomatous inflammation, hemorrhages, and hemosiderin deposits were found most often, whereas in the specimens of the lobe excised after 4 weeks lymphocytic inflammation and fibrosis were mainly observed. No microscopic changes were observed in the thyroid lobes that were not frozen or in the parathyroid glands located inside these lobes or extrathyroidally, either ipsilaterally or contralaterally to the cryotreated thyroid lobes. There was no microscopic damage to other tissues adjacent to the thyroid gland. No rat developed vocal cord dysfunction after cryotherapy and no significant changes in serum calcium level before and after cryotherapy were observed. The results obtained show that it is possible to cryoblate thyroid tissue without damaging the tissues adjacent to the thyroid, as well as to spare function of the recurrent laryngeal nerves and parathyroid glands.