Diagnosis: Follicular neoplasm of thyroid
• The photomicrograph shows a highly cellular specimen containing follicular cells arranged in a microfollicular pattern. This appearance combined with finding scanty or no colloid is suggestive of a follicular neoplasm. Rosette-like microfollicles may not appear as well formed as those in the photomicrograph. Clusters or small, tight aggregates of follicular cells may be seen.
• The follicular cell nuclei are enlarged and often are overlapping. Single naked nuclei (lacking cytoplasm) also are common. Inspissated colloid may be present within the clusters.
• Differentiating follicular adenoma from well-differentiated follicular carcinoma often is impossible based on cytomorphology alone. In well-differentiated follicular carcinoma, especially, only minimal cytologic atypia may be present. Surgical excision with histologic examination is necessary for reliable distinction between follicular adenoma and follicular carcinoma. Although a papillary architecture is absent in the follicular variant of papillary thyroid carcinoma, the nuclear features of this neoplasm are present.
• Hürthle cell tumors are composed almost exclusively of a relatively monotonous population of oncocytic (Hürthle) cells present singly and in clusters.
• Differentiating follicular neoplasia from adenomatous hyperplasia (in nodular goiter) sometimes may be challenging. Large flat sheets of follicular cells, focal oncocytic (Hürthle cell) metaplasia, and abundant colloid favor the latter diagnosis. Fine needle aspiration biopsy of Hashimoto thyroiditis yields oncocytic (Hürthle) cells and a lymphoplasmacytic infiltrate.
