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

.If FNAC repo says follicular adenoma, then hemithyroidectomy is done. If histology repo says follicular carcinoma (capsular and vascular invasion) then completion total thyroidectomy is done. Completion thyroidectomy is done usually within 7 days or after 3 weeks. If frozen section biopsy proves carcinoma then total thyroidectomy is done.FNAC is not very useful in follicular carcinoma as it is difficult to differentiate it from follicular adenoma as main feature in follicular carcinoma is capsular invasion/vascular invasion which are not made out in FNAC. ref:SRB&;s manual of surgery,ed 3,pg no 414