Thyroid Cysts Comprised of Abundant Mature Squamous Cells can be Reported as Benign: A Cytologic Study of 18 Patients with Clinical Correlation

BACKGROUND: A thyroid nodule comprised almost exclusively of mature, benign-appearing squamous cells is an uncommon finding in fine-needle aspiration (FNA) biopsies of thyroid nodules. Reporting such specimens was not originally addressed by The Bethesda System for Reporting Thyroid Cytopathology. The authors correlated the biologic behavior of the specimens with their benign cytologic appearance through clinical, radiographic, and surgical follow-up. METHODS: The pathology archives of 3 tertiary hospitals were searched for thyroid FNA specimens consisting of mature squamous cells without atypia. The authors reviewed all available slides and included only cases that were moderately to highly cellular; nucleated or anucleate squamous cells without atypia comprised the vast majority of the cellularity. Available clinical information and/or thyroid ultrasound examination(s) were reviewed by an endocrinologist or radiologist, respectively. RESULTS: A total of 18 patients (7 men and 11 women; age range, 19-76 years) with 20 nodules met the prespecified inclusion criteria. The average nodule size was 2.1 cm. Common sonographic characteristics included a well-defined appearance, the lack of internal vascularity, a thin outer wall, general hypoechogenicity with low-intermediate internal echoes, and posterior acoustic enhancement. Clinical and radiographic follow-up (mean, 3.8 years; range, <1 to 9 years) was available for 9 patients, and all nodules were stable. All 4 cases with histologic follow-up were benign squamous-lined cysts. CONCLUSIONS: The findings of the current study suggest that thyroid FNA specimens comprised almost exclusively of mature squamous cells can be reported as benign. Cancer Cytopathol 2018;126:336-41. © 2018 American Cancer Society.