Thyroid cryotherapy in an experimental rat model-topography of temperature during therapy and functional results

The aim of this study was to investigate post cryotherapy thyroid function status of normal rat thyroid tissue and to determine the topography of temperature of cryotreated tissues and of tissues adjacent to them. Nitrous oxide cryotherapy was performed in 40 male Wistar rats. They were divided into four groups of 10. In group I, the right thyroid lobe was subjected to cryotherapy and the left lobe was not frozen. In group II, both thyroid lobes were cryotreated. In group III, the right lobe was frozen and the left lobe was excised. In group IV, the thyroid was subjected to neither cryotherapy nor surgery. During cryotherapy, the temperature in various places of the thyroid and in the surrounding tissues was measured. Serum thyrotropin concentrations were determined before an experiment and 4 weeks after in all rats. The results of temperature measurements proved that it is possible to limit cryotherapy to certain areas of thyroid tissue and to spare the neighboring tissues, because they are not subjected to temperatures that are damaging. The effectiveness of cryotherapy was confirmed by functional effect. Cryotherapy changed function of thyroid tissue. There was a statistically significant difference between mean baseline and follow-up concentrations in rats of groups II and III. In both groups hypothyroidism occurred post cryotherapy.