A well differentiated follicular carcinoma of thyroid can be best differentiated from a follicular adenoma by:

Ans is 'c' i.e. Vascular Invasion Repeat All India 09Differentiation between follicular carcinoma and follicular adenoma is dependent on histological criteria of capsular and vascular invasion.This invasion cannot be determined with the preoperative use of FNA cytology. It requires histological analysis. Robbins writes- "While nuclear features are helpful in distinguishing papillary from follicular neoplasms, they are of little value in distinguishing follicular adenomas from minimally invasive follicular carcinomas. This distinction requires extensive histologic sampling of the tumor-capsule-thyroid interface to exclude capsular and/or vascular invasion. The criterion for vascular invasion is applicable only to capsular vessels and vascular spaces beyond the capsule; the presence of tumor plugs within intra-tumoral blood vessels has little prognostic significance. "