Although a wide variety of papillary carcinomas of the thyroid can have abundant granular cytoplasm and may be difficult to distinguish from Hürthle cell lesions in fine-needle aspirations (FNAs), the literature on these tumors is limited. The author described 18 cases with a spectrum of cytologic appearances.
A series of 7089 FNAs was correlated with 1331 subsequent resection specimens. Cases in which the original cytologic and histologic diagnoses included the differential diagnosis of papillary carcinoma or Hürthle cell lesions were identified.
A total of 18 (1.3% of cases with resection) cases were identified. On review, 3 cases had classic features of papillary carcinoma, including nuclear crowding, along with a moderate amount of granular cytoplasm. Four cases had a population of cells that mimicked repair and/or cyst-lining cells with almost no other epithelial cells. In 2 of those 4 cases, the cells were extremely large, and in 2 other cases, they could not be distinguished from typical cyst-lining cells. The remaining 11 cases had cells with overlapping features including pale to granular chromatin, small to medium nucleoli either centrally or eccentrically, occasional grooves, and rare intranuclear inclusions. Typical Hürthle cells also were commonly present. Nuclear crowding was not present, and the cells were in sheets, follicles, or appeared alone. No papillae were identified. On resection, 7 cases were follicular variants of papillary carcinoma, 2 cases occurred in the setting of Hashimoto thyroiditis, and 2 cases had features of the tall-cell variant.
The author concluded that a subset of papillary carcinomas of the thyroid were difficult to distinguish from Hürthle cell lesions or repair and/or cyst-lining cells because of the presence of abundant granular cytoplasm and a lack of nuclear crowding. These tumors were often follicular or cystic variants of papillary carcinoma.