Follicular nodules are the most common source of diagnostic difficulties in the practice of surgical pathology of the thyroid. This is due to a variety of factors, the most salient of which is the lack of well-defined criteria and evidence-based data for the diagnosis of these lesions.
To discuss some of the assumptions that have been accrued over the years regarding the criteria by which we evaluate such lesions.
The information presented herein is based on review of the literature and the author's personal experience.
Thyroid nodules with a predominant follicular growth pattern span the range from benign lesions (hyperplastic nodules, adenomatoid nodules, follicular adenomas) to malignant neoplasms (follicular carcinoma, follicular variant of papillary carcinoma) with a host of intermediate or indeterminate lesions found in between. Advances in immunohistochemistry and molecular pathology have not yet provided a reliable way of separating the borderline or intermediate cases. Low-grade and intermediate or borderline follicular-patterned thyroid lesions are those most often prone to difficulties for interpretation. Newer and potential future approaches for the evaluation of these lesions are discussed.