[Critical reflections on differentiated carcinoma of the thyroid: difficulties, doubts and differential-diagnosis problems]

This work reviews the problems associated with the diagnosis of well differentiated carcinomas of the thyroid (follicular and papillary), which anatomically and clinically can show characteristics not readily distinguishable from those found in thyroid hyperplasia and adenomas. Some features of atypical adenomas and Hurthle cell tumors are detailed, in particular the borderline malignancy of the latter. We have examined the histological parameters useful in diagnosis of follicular carcinoma (cellular polymorphism and size variability with increased and atypical mitoses, invasion of the capsule and vessels, metastasis to lymph nodes and distant organs) and of papillary carcinoma (true papillae, large and crowded nuclei displaying a "ground glass" appearance with grooves and cytoplasmic inclusions and psammoma bodies). The limitations of these parameters are discussed with emphasis on frozen section examination when the lack of time limits examination to few and small tissue fragments. Invasion of the capsule and vessels is not easily detected and the "ground glass" nucleus and presence of grooves are not evident. The biological behavior of well differentiated carcinomas is discussed and, although unpredictable and variable in the single case, is generally that of a slow growing tumor. It is partially influenced by the age of the patient, size and stage of the tumor, invasion of the capsule and vessels and metastatic spread. We have observed that the biological behavior, apparently different in the follicular and papillary forms, appears identical for both tumors when a large number of cases are analyzed. Mention is made of the various surgical choices (total thyroidectomy, subtotal thyroidectomy, lobectomy, different surgical procedures which take into account the various risk factors). No statistically significant differences in recurrences and metastatic spread are obtained by electing more or less aggressive surgery with or without extensive dissection of cervical lymph nodes.