Histopathology of Encapsulated Follicular-Patterned Thyroid Tumors

Abstract

Abstract Encapsulated follicular-patterned thyroid tumors remain diagnostically challenging for pathologists, including experts. The differential diagnosis typically includes hyperplastic/adenomatous nodule, follicular adenoma, follicular thyroid carcinoma, and follicular variant of papillary thyroid carcinoma (FVPTC). Noninvasive follicular thyroid neoplasm with papillary-like features is a new terminology that was recently proposed for a subset of noninvasive FVPTC that has a highly favorable outcome and can be treated in a conservative manner. This is in contrast to invasive-encapsulated FVPTC that clinically behaves similar to follicular thyroid carcinoma and infiltrative FVPTC that behaves like classic PTC. In this review, the differential diagnosis of encapsulated follicular-patterned thyroid neoplasms is discussed, including noninvasive follicular thyroid neoplasm with papillary-like features and its recently revised pathologic criteria. Commonly encountered diagnostic challenges and pitfalls are also reviewed, including criteria for capsular and vascular invasion and minimal diagnostic features of papillary thyroid carcinoma.