Differential Diagnosis for FNA Showing Follicular Cells with Focal Cytologic and Architectural Atypia

• Single Most Likely Diagnosis
  • Benign Follicular Nodule: This is the most likely diagnosis given the presence of benign-appearing follicular cells. The focal cytologic and architectural atypia can sometimes be seen in benign conditions due to sampling error or reactive changes.
• Other Likely Diagnoses
  • Follicular Adenoma with Atypia: This condition is characterized by the presence of follicular cells that are benign but show some degree of atypia, which can be cytologic or architectural. It's a consideration when the atypia is more pronounced than what is typically seen in a benign nodule.
  • Hashimoto Thyroiditis: Although primarily an inflammatory condition, Hashimoto thyroiditis can sometimes show cytologic atypia and architectural distortion, making it a differential diagnosis, especially if the atypia is mild and there are other suggestive features like Hürthle cell changes.
• Do Not Miss Diagnoses
  • Follicular Thyroid Carcinoma: It's crucial not to miss this diagnosis, as it requires surgical intervention. The presence of significant cytologic atypia, increased cellularity, and capsular or vascular invasion (if assessable on the FNA sample) would raise suspicion for follicular carcinoma. However, definitive diagnosis often requires histological examination.
  • Papillary Thyroid Carcinoma with Follicular Features: Although papillary carcinoma typically has distinct nuclear features, some variants can mimic follicular neoplasms. The presence of any papillary nuclear features, even if focal, should prompt consideration of this diagnosis.
• Rare Diagnoses
  • Hyalinizing Trabecular Tumor: A rare thyroid tumor that can show cytologic and architectural atypia, making it a differential diagnosis in challenging cases. It often has a distinctive histological appearance with hyalinized trabeculae.
  • Insular Thyroid Carcinoma: A rare and aggressive form of thyroid cancer that can show a variety of cytologic and architectural patterns, including those mimicking follicular neoplasms. It's characterized by a solid, insular growth pattern and significant cytologic atypia.