Diagnostic imaging of differentiated thyroid carcinoma.

The role of diagnostic imaging in differentiated thyroid carcinoma is analyzed. 99mTc-pertechnetate 123I and 131I scintigraphy allows the evaluation of nodules with their differentiation in cold (hypofunctioning) and hot (functionally autonomous) nodules; thyroid carcinomas are cold nodules even if most of them are benign. On sonography thyroid nodules are well visualized with the definition of their site, number, size (not very useful parameters for the diagnosis of malignancy), echoic structure, and vascularization on color Doppler. The sonographic findings suggestive of differentiated thyroid carcinoma are: solid and hypoechoic structure, irregular ill-defined margins, absent or discontinuous peripheral ring, microcalcification, intranodular vascularization, local lymphadenopathies. These findings are characteristic but not pathognomonic, mostly for papillary carcinoma, while in the frequently isoechoic follicular carcinoma microcalcification and lymph node metastases are rare. Only the finding, although rather infrequent, of the dissemination to adjacent structures (muscles and vessels) is a definite indication for malignancy of a thyroid nodule. Color Doppler sonography plays a major role in the postoperative staging and follow-up, in combination with thyroglobulin determination and 131I whole body scintigraphy and it allows the detection of local and/or laterocervical lymph node recurrence. The most typical sonographic findings of metastatic lymphadenopathy are the roundish shape (length/anteroposterior diameter ratio-L/A < 1.5), not visible or displaced nodal hilum, thickened cortical layer with echoic structure similar to that of thyroid parenchyma, at times with microcalcification, cortical vascularization and dismantled angioarchitecture. CT and MRI are occasionally more useful to evaluate the substernal or retrosternal extension of voluminous thyroid masses and to identify local or distant metastases.