Factors Impacting Thyroid Fine Needle Aspiration Cytology and Algorithm for Cytological Diagnosis in the Japanese System for Reporting FNA Cytology

Since borderline/precursor thyroid tumors are now established in the thyroid tumor classification, the next required step is to establish cytological categories to accomodate these tumors. How to handle these categories is the key for diagnostic system for thyroid FNA cytology. The Japanese diagnostic system is a histological-oriented classification by which the indeterminate category is sub-classifies into follicular adenoma/follicular carcinoma (RAS-like tumor) lineage and papillary carcinoma (BRAF-like tumor) lineage. The author proposed several histological type oriented classifications of thyroid FNA cytology in this chapter which were modified from the Japanese system. The author believes they are useful for selection of optimal molecular tests and/or ancillary tests for more definite diagnoses of indeterminate nodules. This is the key to solve the problems with the so-called indeterminate categories. With the aide of available clinical tests, including molecular tests, more definite diagnosis will help reduceing numbers of diagnostic surgery and over treatment of indolent thyroid tumors.