Slide 2.17
A follicular carcinoma is composed of uniform cells forming small follicles containing colloid. Nuclear features of papillary carcinoma are not present.

Note the thick fibrous capsule which is focally penetrated by tumor cells (capsular invasion).

Slide 2.18
Within the capsule of this nodule there is a focus of vascular invasion (arrow), consisting of nests of tumor cells within an endothelial-lined space.