Answer: Papillary carcinoma, tall cell variant

Histology: On gross inspection, there is a 4 cm mass centered in the thyroid with extension into peithyroidal soft tissues. Microscopically, the tumor demonstrates a “hyperpapillary” architecture – long delicate papillary fronds run in parallel arrays. The cells lining the fibrovascular cores are elongated and have cytoplasm that is tall (i.e. cytoplasm that is at least twice as high as it is wide) and eosinophilic. The nuclei tend to be uniformly aligned without significant overlapping or stratification. Longitudinal nuclear grooves and intranuclear inclusions are readily identified.

Discussion: The tall cell variant of papillary thyroid carcinoma (PTC) is recognized as an aggressive subtype of PTC. Compared to conventional PTC, it tends to involve an older group of patients, and it tends to present at a higher tumor stage with an increased occurrence of extrathyroidal extension, local recurrence and metastatic spread.

As first described by Hawk and later by Hawk and Hazard, the tall cell subtype of PTC is defined by the presence of elongated cells that are twice as tall as they are wide. Most would agree that the tall cells must comprise at least 30% of the cell population before designating a PTC as a tall cell variant. Unlike the columnar cell variant, the nuclei are not stratified but are more uniformly aligned. The distinction is important because the tall cell variant is not as aggressive as the columnar variant. Not only are the cells tall, but they have oncocytic-like cytoplasm. Accordingly, they commonly enter the differential diagnosis of oncocytic neoplasms including Hurthle cell carcinoma. In contrast to Hurthle cell neoplasms, the nuclear atypia of PTC, including intranuclear inclusions and contour irregularities, are well developed in the tall cell variant.