Follicular Thyroid Adenoma with Papillary Architecture

     A 23-year-old woman underwent left thyroid lobectomy and isthmusectomy for a 2 cm diameter firm mass on the left side of the neck that was also visualized on ultrasonography. The specimen consisted of a 22-gram thyroid gland composed of the left lobe, isthmus and a pyramidal lobe. Cut section of the left lobe showed a 3.5 cm diameter solitary, discrete and encapsulated mass with a tan lobulated and solid cut surface. The rest of the thyroid tissues had red-brown meaty cut surfaces.      Microscopic section shows a follicular-patterned proliferation enclosed by a thin fibrous capsule with frequent Sanderson polster-like papillary excrescences. (Figures 1 and 2) Both the follicular and the papillary structures are lined by cuboidal to columnar follicular epithelial cells that had ample eosinophilic to pale cytoplasm and uniformly sized, minimally enlarged, generally round, and monolayered nuclei without nuclear grooving, folds, pseudoinclusions, and chromatin clearing. There are no mitotic figures seen. Some of the papillary structures have delicate vascular cores. (Figure 3) There are no psammoma bodies noted. The follicles contain variable amounts of pale eosinophilic colloid ranging from colloid-poor crowded follicles to those with ample colloid that have frequent peripheral scalloping. (Figure 4) Exhaustive sections failed to disclose capsular or vascular invasion. Based on the microscopic features, a diagnosis of follicular adenoma with papillary architecture was rendered.