General and Systemic Histopathology, C601&C602
How do we distinguish an adenoma from a malignant lesion in the thyroid? What features tell us this is benign? Does it have any malignant potential?
The three principal things distinguishing this as a benign adenoma are: (1) a defining capsule, (2) the follicles and follicular cells are distinct and different from the surrounding thyroid tissue and (3) there is compression (as opposed to invasion) of the surrounding normal thyroid. Principal feature of malignancy of the thyroid would include papillary growths of the tumor, an invasive growth pattern and nuclear atypia of the malignant cells. At least these rules apply for the most common form of thyroid cancer. So far as I am aware, and adenoma has no malignant potential.