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 cr yotherapy of one thyroid lobe in twenty 12-week male Wistar rats was perfor med. After 2 and 4 weeks, the cryotreated thyroid lobe and the second lobe alone with a part of the trachea, esophagus, and the subhyoid muscles adher ing to the thyroid were excised and assessed macro- and microscopically. Th e macroscopic evaluation, performed 2 and 4 weeks postcryotherapy, revealed atrophy of the cryotreated lobe in 4 and 3 rats, respectively, and reducti on of the cryotreated lobe dimensions in 6 and 7 rats, respectively In the specimens of the lobes excised 2 weeks following cryotherapy, examined micr oscopically, necrosis, granulomatous inflammation, hemorrhages, and hemosid erin deposits were found most often, whereas in the specimens of the lobe e xcised after 4 weeks lymphocytic inflammation and fibrosis were mainly obse rved. No microscopic changes were observed in the thyroid lobes that were n ot frozen or in the parathyroid glands located inside these lobes or extrat hyroidally, either ipsilaterally or contralaterally to the cryotreated thyr oid lobes. There was no microscopic damage to other tissues adjacent to the thyroid gland. No rat developed vocal cord dysfunction after cryotherapy a nd no significant changes in serum calcium level before and after cryothera py were observed. The results obtained show that it is possible to cryoblat e thyroid tissue without damaging the tissues adjacent to the thyroid, as w ell as to spare function of the recurrent laryngeal nerves and parathyroid glands. (C) 1999 Academic Press.