Answer: Papillary thyroid carcinoma

Histology: The tumor a well circumscribed nodule that appears distinct from the remainder of the thyroid. On low magnification, most of the tissue in the nodule appears similar to the surrounding normal thyroid. Focally, within the nodule, paler more crowded areas are seen. On higher magnification the nuclei in these crowded areas are noted to be overlapping, large, and optically clear. Nuclear grooves are also occasionally observed. Other areas with rudimentary papillary formations can be seen.

Discussion: A well-circumscribed nodule is seen which contains predominantly bland follicles. Scattered throughout this nodule are areas with features including enlargement of the nuclei, clearing of the chromatin, nuclear overlapping and nuclear grooves. These features are diagnostic of papillary carcinoma and are helpful in distinguishing this nodule from follicular adenoma and graves disease, which would have more benign appearing nuclei. Since multiple areas with these classic features for papillary carcinoma were seen scattered throughout the nodule, the diagnosis of follicular variant of papillary thyroid carcinoma was made, rather than papillary microcarcinoma arising in an adenomatoid nodule.

Papillary carcinoma of the thyroid is associated with the RET oncogene. The overall prognosis for patients with papillary cancer is excellent. Extra-thyroid extension into soft tissues of the neck is seen in approximately twenty five percent of patients. Involvement of cervical lymph nodes is very common and does not adversely affect the prognosis. Factors that are associated with a worse prognosis are age greater than forty years, extra thyroid extension, large tumor size, multicentricity, distant metastasis, and presence of anaplastic foci.