CQ21. Is It Possible to Diagnose Follicular Carcinoma on Preoperative FNA or Intraoperative Frozen Section Diagnosis?
Follicular carcinoma is defined as “a malignant tumor arising from follicular epithelial cells lacking the typical findings of the nuclei for papillary carcinoma,” but the diagnosis is extremely difficult. The follicular structure of follicular carcinoma is often very well differentiated, to the extent that it is difficult to discriminate from that of the normal thyroid. Generally, structural atypia, cellular atypia and nuclear atypia are important findings to establish malignant tumors. These atypia are clearly observed in FNA specimens of most papillary carcinomas and the treatment strategy for papillary carcinoma can be determined preoperatively. However, follicular carcinoma can be diagnosed only when the presence of capsular and/or vascular invasion is identified on pathological examination, requiring the tissue specimens from a number of lesions, including the whole capsule. A follicular tumor with these pathological findings is diagnosed as follicular carcinoma and in their absence as follicular adenoma. The above-mentioned atypia is not included in the diagnostic criteria of follicular carcinoma.
KeywordsPathological Examination Vascular Invasion Papillary Carcinoma Normal Thyroid Follicular Carcinoma
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