Table 3.

Histologic Criteria for the Diagnosis of Variants of Papillary Thyroid Carcinoma

Variant	Proportion of variant tumor cells	Major histologic features
Follicular variant	Exclusively	No true papillae, follicular growth, PTC nuclear features
Tall cell variant	≥30%	Growth: elongated follicles, closely packed papillae Tall cells: two to three times taller than wide, abundant eosinophilic cytoplasm, sharply delineated cell borders
Columnar cell variant	≥30%	More elongated cells than tall cell variant, pseudostratified hyperchromatic nuclei, lack conventional PTC nuclei, subnuclear cytoplasmic vacuole
Hobnail variant	≥30%	Loss of cellular cohesion, micropapillary, apically located nuclei, prominent nucleoli, pleomorphic nuclei, mitosis
Solid variant	All or nearly all	Solid, trabecular, or nested (insular) growth, PTC nuclear features, absence of high mitotic figures and/or necrosis
Diffuse sclerosing variant	NA	Dense sclerosis, numerous psammoma bodies, lymphatic invasion, chronic lymphocytic thyroiditis, squamous metaplasia
Other variants	Predominantly (>50%)

PTC, papillary thyroid carcinoma; NA, not available.