2023 Volume 62 Issue 1 Pages 32-37
Background : Follicular carcinoma, oncocytic variant (FCOV) and follicular adenoma, oncocytic variant (FAOV), included in the histological diagnosis of thyroid tumors in Japan, are also called Hürthle cell carcinoma (oncocytic carcinoma) and Hürthle cell adenoma, respectively, according to the World Health Organization classification (2017). As FCOV and FAOV are classified based on the presence on histopathological examination of capsular invasion and/or vascular invasion, cytological differentiation was considered impossible ; however, recent studies have shown cytological differences between FCOV and FAOV. We attempted to review the cytological differences between FCOV and FAOV and to evaluate the fine-needle aspiration cytology findings of a thyroid tumor that was histopathologically diagnosed as FCOV 11 years after the initial cytology.
Case : A Japanese woman in her 40s was referred to our hospital for surgical treatment of a thyroid tumor. She had been under follow-up for a thyroid nodule for 10 years at a nearby hospital, and the nodule had recently increased in size from 2 cm to 6 cm. No metastases were observed. Surgery was performed and histopathology confirmed the diagnosis of FCOV. Fine-needle aspiration cytology of the thyroid tumor performed 11 years ago at our hospital had led to the suspicion of an oncocytic neoplasm, because oncocytic cells (discohesive, multiple nuclei, distinct nucleoli, large cell dysplasia, and transgressing blood vessels) were predominantly observed. Some of these cytological features are seen more frequently in FCOV than in FAOV, according to a literature review.
Conclusion : In the present case, FCOV could have been suspected ; however, decisions on the clinical management of FCOVs should not be based on cytological evaluation alone.
