Diagnosis of Follicular Neoplasm

Abstract

There are several reporting systems of thyroid cytopathology. And the aspirate of follicular neoplasm is diagnosed in different terminology in each reporting system. However, each reporting system has similar diagnostic criteria for follicular neoplasm. The category for follicular neoplasm refers to cellular aspirate comprised of monotonous follicular cells with a microfollicular pattern and scant or absent colloid and exclusion of cases with papillary carcinoma type nuclear features. Also, the samples composed exclusively of Hurthle/oncocytic cells are included in this category in all reporting systems. According to the fifth edition of the 2022 WHO classification of tumors of endocrine and neuroendocrine organs, follicular nodules comprise benign tumors, low-risk neoplasms, and malignant neoplasms. And the cytologic findings of follicular adenoma/carcinoma or Hurthle cell adenoma/carcinoma overlap with other thyroid follicular-patterned lesions, including nodular hyperplasia, noninvasive follicular thyroid neoplasm with papillary-like nuclear features, and even follicular variant papillary carcinoma. Although there are reported cytologic features for follicular thyroid carcinoma or Hurthle cell carcinoma, such as more cellularity, more trabecular patterned microfollicle, prominent nucleoli, and large cell dysplasia, the limitations in the cytologic interpretation of follicular-patterned lesions are present. The precise diagnosis for these lesions should be made after thoroughly examining surgical specimens to confirm capsular and/or vascular invasion. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2019, 2023, corrected publication 2024.