Thyroid follicular carcinoma is almost entirely unifocal.( papillary carcinoma may be multifocal in 20% of cases.) The extent of the tumor pseudocapsular involvement by follicular cells must be determined for separation between low risk and high risk follicular cancers. Minor involvement includes scattered cells in a portion of the tumor pseudocapsule with occasional blood vessel invasion, while major involvement implies extensive breaching of the tumor pseudocapsule, exttensive blood vessel involvement , or thyroid follicular cells outside the tumor pseudocapsule. In minor involvement, there is no alteration of the survival curve from normal population but in major involvement, the mortality rate may be as high as 50 percent.