Answer: Papillary carcinoma, diffuse sclerosing type

Histology: Grossly, a mass was not apparent, though the thyroid gland was diffusely enlarged. A “gritty” texture was noted on cut section. Histologically, at low power the gland was characterized by bands of fibrosis, chronic thyroiditis with germinal centers, and abundant calcifications. At higher power, it was evident that virtually every angiolymphatic space was occupied by carcinoma and/or psamomma bodies. The tumor exhibit papillary architecture with foci of squamous metaplasia.

Discussion: The diffuse sclerosing variant is a very rare form of papillary thyroid carcinoma typically affects children or young adults, and has a strong female predominance. The tumor is characterized by:
1) diffuse involvement of the thyroid gland, often without a grossly evident mass;
2) bands of sclerosis;
3) a lymphocytic infiltrate;
4) extensive lymphovascular invasion;
5) abundant psammoma bodies; and 6) squamous metaplasia.

Diffuse sclerosing variant is considered an aggressive form of thyroid cancer, with higher rates of lymph node and distant metastases. However, in large series this tumor seems to have a favorable outcome, perhaps due to the generally young age of the patients.