Slide 2.15
This 6.0 cm well-circumscribed, hemorrhagic nodule centered in the isthmus was diagnosed as follicular carcinoma (capsular and vascular invasion were identified microscopically). Note the beefy-red, glistening normal thyroid parenchyma in the right and left lobes. This lesion would be difficult to separate from a follicular adenoma based on gross examination only. Follicular carcinoma is the second most common form of thyroid cancer (10-20% of cases).

Slide 2.16
Another case of follicular carcinoma. In this case the tumor is tan-white, solid, and infiltrative, with multiple smaller nodules budding from the central mass. Microscopically, capsular and vascular invasion (the hallmark of follicular thyroid carcinoma) were identified.