Diagnostic scintigraphy in postoperative staging and follow-up of differentiated thyroid carcinoma.
In the last decade new knowledge has been acquired on the cellular and molecular biology, growth and prognostic factors responsible for the clinical evolution and response to therapy of differentiated thyroid carcinoma. At the same time, the procedures for early diagnosis of small (occult), poorly aggressive thyroid tumors as high resolution neck sonography combined with fine needle aspiration have greatly advanced. This led to reconsider the definition of the most adequate management with a more frequent use of combined radiochemotherapy and surgery for aggressive forms and simple lobectomy for occult tumors. These progressive changes in the therapeutic approach required the diversification of corresponding follow-up protocols of differentiated thyroid carcinoma. The efforts of radiologists and nuclear physicians in particular, were focused on two sectors: 1) the early visualization of metastases no longer able of radioiodine uptake where, therefore, this radionuclide cannot be used for diagnosis or therapy; 2) the diagnosis of metastases in patients undergoing subtotal thyroidectomy. In these cases, 131I has no role in imaging and the determination of serum TG is not very significant. To assess the diagnostic role of nuclear medicine in these situations, the main characteristics of radioiodine scintigraphy with particular reference to the use of high 131I doses and of recombinant human TSH, the diagnostic potentialities of scintigraphy with the most common oncotropic tracers other than 131I were analyzed.