Multiple squamous cells in thyroid fine needle aspiration: Friends or foes?

Abundant squamous cells are rarely encountered in thyroid FNA with only few case reports noted in the literature. Their presence and cytologic features may pose a diagnostic dilemma and challenges for proper classification and follow-up. We intend to gain more insight into the frequency of this finding and its clinical significance.

Our electronic records were searched over 16 years to reveal 15 thyroid FNAs with abundant squamous cells. The available cytology and surgical resection slides were reviewed and radiologic records and clinical follow-up was documented.

Only 15 out of 8811 thyroid FNAs from our department contained predominantly squamous cells (0.17%) of which two were interpreted as nondiagnostic, four as atypical, eight as benign, and one malignant. Surgical follow-up was available in eight cases only with benign lesions representing the majority of the cases (squamous metaplasia in Hashimoto thyroiditis, benign epidermoid/branchial cleft or thyroglossal duct cysts, and one case squamous cell carcinoma). The cases without surgical resection were stable on subsequent ultrasound studies.

Thyroid aspirates with predominance of squamous cells cannot be classified in the current Bethesda categories. Even when interpreted as atypical or equivocal, the squamous cells present in our small case series were mostly benign. The only malignant case was easily identified cytologically because of its higher degree of differentiation. The most common pitfall for atypical squamous cells in these aspirates was squamous metaplasia in the setting of Hashimoto thyroiditis and degenerative changes. Diagn. Cytopathol. 2016;44:676-681. © 2016 Wiley Periodicals, Inc.