Follicular neoplasm of the thyroid—vanishing cytologic diagnosis?

Abstract

The significance of making a diagnosis of follicular neoplasm on fine needle aspiration (FNA) biopsy remains a controversial issue, considering that the diagnosis of follicular carcinoma is based on histological criteria and the significantly decreasing incidence of follicular carcinoma in the general population. On FNA the main differential diagnoses of follicular neoplasm includes follicular variant of papillary carcinoma (FVPC), follicular adenoma, follicular carcinoma and benign solitary nodule occurring in a goiter. Several studies have looked at immunohistochemical and molecular markers to distinguish benign from malignant lesions but none of them have proved to be infallible. Although, FVPC is a distinct entity from the follicular neoplasm group, it is not always possible to separate it from the other follicular lesions because of overlapping cytologic features and often-sporadic presence of nuclear features, follicular variant of papillary carcinoma remains the main pitfall in a diagnosis of follicular neoplasm. Since a significant number of cases that are malignant on follow-up are usually FVPC, consequently, follicular neoplasm is an essential diagnostic consideration on FNA. In addition, follicular carcinoma, despite a decreasing incidence continues to be a real entity. Therefore, it is essential that follicular neoplasm continue to be part of our diagnostic repertoire.