Table 7.

Thyroid Histopathology Using a 5-Point Grading Scale

Follicular cell height
Grade 1	Prominent number of follicles (>25%) were lined by an attenuated epithelium with scant eosinophilic cytoplasm and a flattened hyperchromatic nucleus. The majority of the remaining follicles were lined by a low cuboidal epithelium with a round to oval nucleus and a cell height that was ≤1.5× the height of the nucleus.
Grade 2	Most follicles were lined by a cuboidal to slightly columnar epithelium, often with a flocculent to finely vacuolated eosinophilic cytoplasm, round to oval nucleus, and the cell height which was ≤2× (twice) the height of the nucleus.
Grade 3	Most follicles were lined by a slightly columnar epithelium with a foamy to vacuolated eosinophilic cytoplasm and a round nucleus; the cell height is 2× to 2.5× the height of the nucleus.
Grade 4	Similar nuclear and cytoplasmic characteristics as described for Grade 3 above. Most follicles were lined by a distinctly columnar epithelium with a cell height 2.5× to 3× the height of the nucleus.
Grade 5	Most follicles were lined by a distinctly columnar epithelium with a cell height >3× the height of the nucleus.
Colloid area
Grade 1	Absence of colloid or decreased colloid in >67% of thyroid follicles.
Grade 2	Same as Grade 1 above, except the condition affected 34–66% of the follicles.
Grade 3	Most follicles were small, even at the periphery, with 25–33% being collapsed with no visible colloid or decreased amount of colloid.
Grade 4	Most follicles contained variable amounts of eosinophilic to grayish-pink colloid with the peripheral follicles generally being larger with more abundant colloid compared to the innermost follicles.
Grade 5	Most follicles were filled with eosinophilic colloid with only a slight variation in follicular size.