Ans. is 'c' i.e., Capsular invasion Differentiating feature of follicular adenoma from follicular carcinoma. o The hallmark of all follicular adenomas is the presence of on intact ,wall-formed capsule encircling the tumor. o Careful evaluation of the integrity of the capsule is therefore critical in distinguishing follicular adenomas from follicular carcinomas which demonstrate capsular and /or vascular invasion . o Huhle cells are seen both in follicular adenomas and follicular carcinoma (Note -Huhle cells are also seen in hashimoto thyroiditis) Differentiation of follicular adenoma from multinodular goiter Multinodular goiter lacks well formed capsule while follicular adenoma has well formed capsule. o Multinodular goiter produce less compression of the adjacent thyroid parenchyma ,while follicular adenoma comresses the adjacent thyroid. o In multinodular goiter the involved and uninvolved (normal ) thyroid have similar growth pattern , on the other hand growth pattern within the adenoma is distinct from the adjacent non- neoplastic thyroid.